U.S. patent application number 14/133902 was filed with the patent office on 2014-06-26 for methods of making a drilling tool with low friction coatings to reduce balling and friction.
This patent application is currently assigned to EXXONMOBIL RESEARCH AND ENGINEERING COMPANY. The applicant listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Jeffrey Roberts Bailey, Mehmet Deniz Ertas, Tabassumul Haque, HyunWoo Jin, Russell Robert Mueller, Adnan Ozekcin, Srinivasan Rajagopalan, Bo Zhao.
Application Number | 20140173995 14/133902 |
Document ID | / |
Family ID | 50030450 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140173995 |
Kind Code |
A1 |
Bailey; Jeffrey Roberts ; et
al. |
June 26, 2014 |
METHODS OF MAKING A DRILLING TOOL WITH LOW FRICTION COATINGS TO
REDUCE BALLING AND FRICTION
Abstract
Provided are methods to make a drilling tool with low friction
coatings to reduce balling and friction. In one form, the method
includes providing one or more drilling tool components with
specified locations for fitting cutters, inserts, bearings,
rollers, additional non-coated components, or combinations thereof;
cleaning the one or more drilling tool components; applying masking
for fitting cutters, inserts, bearings, rollers, additional
non-coated components or combinations thereof; applying a
multi-layer low friction coating to the cleaned specified
locations; removing the masking from the cleaned and coated
specified locations of the one or more drilling components;
inserting cutters and inserts and assembling moving parts to the
cleaned and coated specified locations of the one or more drilling
tool components; and assembling the one or more drilling tool
components to form a drilling tool.
Inventors: |
Bailey; Jeffrey Roberts;
(Houston, TX) ; Rajagopalan; Srinivasan; (Easton,
PA) ; Haque; Tabassumul; (Deptford, NJ) ;
Ozekcin; Adnan; (Bethlehem, PA) ; Ertas; Mehmet
Deniz; (Bethlehem, PA) ; Jin; HyunWoo;
(Easton, PA) ; Zhao; Bo; (Houston, TX) ;
Mueller; Russell Robert; (Washington, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
|
|
Assignee: |
EXXONMOBIL RESEARCH AND ENGINEERING
COMPANY
Annandale
NJ
|
Family ID: |
50030450 |
Appl. No.: |
14/133902 |
Filed: |
December 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13724403 |
Dec 21, 2012 |
|
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14133902 |
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Current U.S.
Class: |
51/295 ; 51/297;
51/307 |
Current CPC
Class: |
C23C 28/343 20130101;
C23C 28/322 20130101; C23C 16/0272 20130101; E21B 10/00 20130101;
C23C 28/347 20130101; C23C 14/024 20130101; C23C 28/42 20130101;
E21B 17/10 20130101; C23C 28/044 20130101; B24D 18/0027 20130101;
C23C 28/046 20130101 |
Class at
Publication: |
51/295 ; 51/307;
51/297 |
International
Class: |
B24D 18/00 20060101
B24D018/00 |
Claims
1. A method of manufacturing a drilling tool comprising: providing
one or more drilling tool components with specified locations for
fitting cutters, inserts, bearings, rollers, additional non-coated
components, or combinations thereof; cleaning said one or more
drilling tool components with specified locations to remove oil,
organic compounds, and/or adsorbates; applying masking to said
cleaned specified locations for fitting cutters, inserts, bearings,
rollers, additional non-coated components or combinations thereof;
applying a multi-layer low friction coating to said cleaned
specified locations, wherein said multi-layer low friction coating
comprises: i) an under layer selected from the group consisting of
CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN, TiAlSiN and
combinations thereof, wherein the under layer ranges in thickness
from 0.1 to 100 .mu.m, ii) an adhesion promoting layer selected
from the group consisting of Cr, Ti, Si, W, CrC, TiC, SiC, WC, and
combinations thereof, wherein the adhesion promoting layer ranges
in thickness from 0.1 to 50 .mu.m and is contiguous with a surface
of the under layer, and iii) a functional layer selected from the
group consisting of a fullerene based composite, graphene, a
diamond based material, diamond-like-carbon (DLC), and combinations
thereof, wherein the functional layer ranges from 0.1 to 50 .mu.m
and is contiguous with a surface of the adhesion promoting layer.
wherein the adhesion promoting layer is interposed between the
under layer and the functional layer, wherein the coefficient of
friction of the functional layer of the low friction coating as
measured by the block on ring friction test is less than or equal
to 0.15, and wherein the abrasion resistance of the low friction
coating as measured by the modified ASTM G105 abrasion test yields
a wear scar depth of less than or equal to 20 .mu.m and a weight
loss less than or equal to 0.03 grams; removing the masking from
said cleaned and coated specified locations of said one or more
drilling components; inserting cutters and inserts and assembling
moving parts to the cleaned and coated specified locations of the
one or more drilling tool components; and assembling the one or
more drilling tool components to form a drilling tool.
2. The method of claim 1, wherein the under layer is contiguous
with a surface of a substrate.
3. The method of claim 2, wherein the substrate is selected from
the group consisting of steel, stainless steel, hardbanding, an
iron alloy, an aluminum based alloy, a titanium based alloy,
ceramics and a nickel based alloy.
4. The method of claim 3, wherein the hardbanding comprises a
cermet based material, a metal matrix composite or a hard metallic
alloy.
5. The method of claim 1, wherein the functional layer is a diamond
based material.
6. The method of claim 5, wherein the diamond based material is
chemical vapor deposited (CVD) diamond or polycrystalline diamond
compact (PDC).
7. The method of claim 1, wherein the functional layer is
diamond-like-carbon (DLC).
8. The method of claim 7, wherein the diamond-like-carbon (DLC) is
selected from the group consisting of ta-C, ta-C:H, DLCH, PLCH,
GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and combinations
thereof.
9. The method of claim 1, wherein the under layer hardness ranges
from 800 to 3500 VHN.
10. The method of claim 1, wherein the adhesion promoting layer
hardness ranges from 200 to 2500 VHN.
11. The method of claim 1, wherein the functional layer hardness
ranges from 1000 to 7500 VHN.
12. The method of claim 1, further including a gradient at the
interface of the under layer and the adhesion promoting layer
ranging from 0.01 to 10 .mu.m.
13. The method of claim 1, further including a gradient at the
interface of the adhesion promoting layer and the functional layer
ranging from 0.01 to 10 .mu.m.
14. The method of claim 1, further including a second adhesion
promoting layer selected from the group consisting of Cr, Ti, Si,
W, CrC, TiC, SiC, WC, and combinations thereof, wherein the second
adhesion promoting layer ranges in thickness from 0.1 to 50 .mu.m
and is contiguous with a surface of the functional layer, and a
second functional layer selected from the group consisting of a
fullerene based composite, graphene, a diamond based material,
diamond-like-carbon (DLC), and combinations thereof, wherein the
second functional layer ranges from 0.1 to 50 .mu.m and is
contiguous with a surface of the second adhesion promoting
layer.
15. The method of claim 14, further including a second under layer
interposed between the functional layer and the second adhesion
promoting layer, wherein the second under layer is selected from
the group consisting of CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN,
TiSiCN, TiAlSiN and combinations thereof, wherein the second under
layer ranges in thickness from 0.1 to 100 .mu.m.
16. The method of claim 14, wherein the second functional layer is
diamond-like-carbon (DLC).
17. The method of claim 16, wherein the diamond-like-carbon (DLC)
is selected from the group consisting of ta-C, ta-C:H, DLCH, PLCH,
GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and combinations
thereof.
18. The method of claim 1, further including from 1 to 100 series
of incremental coating layers, wherein each series of incremental
coating layers includes a combination of an incremental adhesion
promoting layer, an incremental functional layer and an optional
incremental under layer, wherein the each series of incremental
coating layers is configured as follows: (i) wherein the optional
incremental under layer is selected from the group consisting of
CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN, TiAlSiN and
combinations thereof; ranges in thickness from 0.1 to 100 .mu.m;
and is contiguous with a surface of the functional layer and the
incremental adhesion promoting layer: wherein the optional
incremental under layer is interposed between the functional layer
and the incremental adhesion promoting layer, (ii) wherein the
incremental adhesion promoting layer is selected from the group
consisting of Cr, Ti, Si, W, CrC, TiC, SiC, WC, and combinations
thereof; ranges in thickness from 0.1 to 50 .mu.m; and is
contiguous with a surface of the functional layer or optional
incremental under layer, and the incremental functional layer:
wherein the incremental adhesion promoting layer is interposed
between the functional layer and the incremental functional layer
or between the optional incremental under layer and the incremental
functional layer (iii) wherein the incremental functional layer is
selected from the group consisting of a fullerene based composite,
graphene, a diamond based material, diamond-like-carbon (DLC), and
combinations thereof; ranges from 0.1 to 50 .mu.m in thickness; and
is contiguous with a surface of the incremental adhesion promoting
layer.
19. The method of claim 18, wherein the incremental functional
layer is diamond-like-carbon (DLC).
20. The method of claim 19, wherein the diamond-like-carbon (DLC)
is selected from the group consisting of ta-C, ta-C:H, DLCH, PLCH,
GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and combinations
thereof.
21. The method of claim 18, wherein the optional incremental under
layer hardness ranges from 800 to 3500 VHN.
22. The method of claim 18, wherein the incremental adhesion
promoting layer hardness ranges from 200 to 2500 VHN.
23. The method of claim 18, wherein the incremental functional
layer hardness ranges from 1000 to 7500 VHN.
24. The method of claim 18, further including a gradient at the
interface of the optional incremental under layer and the
incremental adhesion promoting layer ranging from 0.01 to 10
.mu.m.
25. The method of claim 18, further including a gradient at the
interface of the incremental adhesion promoting layer and the
incremental functional layer ranging from 0.01 to 10 .mu.m.
26. The method of claim 1, wherein the surface roughness of the
functional layer ranges from 0.01 .mu.m to 1.0 .mu.m Ra.
27. The method of claim 18, wherein the surface roughness of the
outermost incremental functional layer ranges from 0.01 .mu.m to
1.0 .mu.m Ra.
28. The method of claim 1, wherein the counterface wear scar depth
as measured by the block on ring friction test is less than or
equal to 500 .mu.m.
29. The method of claim 1, wherein the abrasion resistance of the
low friction coating as measured by the modified ASTM G105 abrasion
test yields a wear scar depth and a weight loss at least 5 times
lower than a single layer coating of the same functional layer.
30. The method of claim 1 wherein the one or more drilling tool
components is comprised of a carbon steel material that has
hardfacing material applied to at least a portion of the area to be
coated.
31. The method of claim 1 wherein at least a portion of the one or
more drilling tool components is comprised of a carbide matrix
material.
32. The method of claim 1 wherein at least one cutter or insert is
brazed to at least one of the one or more drilling tool components
of the drilling tool prior to the cleaning step.
33. The method of claim 32 wherein the one or more drilling tool
components are cooled during the brazing process.
34. The method of claim 1 wherein at least one cutter or insert is
brazed to at least one of the one or more drilling tool components
of the drilling tool prior to the step of applying the multi-layer
low friction coating to said one or more drilling tool
components.
35. The method of claim 34 wherein the one or more drilling tool
components are cooled during the brazing process.
36. The method of claim 1 wherein the cleaning step includes a
solvent bath.
37. The method of claim 1 wherein the cleaning step includes ion
etching.
38. The method of claim 1 further including a processing step after
said preparing step and prior to said cleaning step, wherein said
processing step comprises polishing at least a portion of the
surface of said drilling tool components to a minimum surface
roughness specification of less than 1 .mu.m Ra.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-in-Part of and claims
priority to U.S. patent application Ser. No. 13/724,403 filed on
Dec. 21, 2012 and incorporated by reference herein in its
entirety.
FIELD
[0002] The present disclosure relates to the field of coatings with
improved properties. It more particularly relates to methods of
making a drilling tool with such coatings to reduce balling and
friction, for the purpose of constructing a wellbore to produce
hydrocarbons.
BACKGROUND
Balling and Friction Characteristics of Drilling Tools
[0003] In rotary drilling operations, a drill bit is attached to
the end of a bottom hole assembly which is attached to a drill
string comprising drill pipe and tool joints which may be rotated
at the surface by a rotary table or top drive unit. The weight of
the drill string and bottom hole assembly causes the rotating bit
to bore a hole in the earth. Alternatively, coiled tubing may
replace drill string in the drilling assembly. Rotation of the
drill string provides power through the drill string and bottom
hole assembly to the bit. In coiled tubing drilling, power is
delivered to the bit by the drilling fluid pumps. The rate of
progress of the drilling process is determined in part by how
effectively the bit is able to drill ahead to "make hole."
[0004] Bit balling has been identified as a primary cause of
ineffective bit performance when drilling shale with water based
mud. It can also be problematic when drilling certain carbonate
formations. Bit balling is a result of cohesion between the
cuttings, creating a blockage in the open slot areas of a bit.
Cuttings made by a drill bit can also adhere to the surface of the
bit, particularly in regions that have low flow velocity. Bit
balling can occur on bit surfaces where the shear stress applied by
the drilling fluid is insufficient to overcome the sticking forces
to keep the cuttings flowing. Irreversible bit balling refers to
severe balling that may require tripping out of the hole to clean
or replace the bit. Therefore, it is crucial to mitigate bit
balling in some field drilling environments. This can potentially
provide substantial economic benefits including saving trips out of
the hole and reducing drilling cost.
[0005] Drilling tools such as under-reamers and stabilizers may
suffer similar dysfunction as drill bits in that they also have
elements that may ball with shale cuttings, particularly in
water-based drilling mud. Stabilizer elements have longitudinal or
spiral blades that protrude from the tool body. Similarly,
under-reaming tools have protruding arms or blades that have
cutting elements that are designed to enlarge the hole to a
prescribed diameter. In both devices, fluid loaded with cuttings
pass through channels between the blades, and cuttings accretion
can occur, which can impede the drilling progress.
[0006] With the increasing development of unconventional resources,
such as shale gas fields, bit balling mitigation plays an
increasingly important role. "Shale" is a fine-grained elastic
sedimentary rock that may be found in formations, and may often
have a mean grain size of less than 0.0625 mm. Shale typically
includes laminated and fissile siltstones and claystones. These
materials may be formed from clays, quartz, and other minerals that
are found in fine-grained rocks. Non-limiting examples of shales
include Barnett, Fayetteville, and Woodford in North America.
Because of its high clay content, shale tends to absorb water from
a water-based drilling mud which results in swelling and wellbore
failure. Industry-wide, more than half of the formations drilled
have significant shale content.
[0007] Bit balling is a founder point in the drilling process which
limits the rate of penetration (ROP) and overall drilling
efficiency. It is normally thought to occur when drilling shales or
some shaly carbonate formations, particularly when using
water-based drilling fluids. In addition, high friction on a bit
surface yields higher parasitic torque, again limiting drilling
efficiency. Having a low surface energy and low friction coating in
the junk slots or flow path of cuttings and on the bit surface can
reduce both of these dysfunctions and improve drilling ROP and
efficiency.
[0008] There is also some evidence that the founder point of a bit
is in some instances related to clearing cuttings from the bit and
bottomhole pattern, even when traditional bit-balling conditions
are not present. Longer blade standoff to provide a larger gap
sometimes leads to increased drilling rates. One tradeoff in such a
design is that the larger flow cross-section for the same flow rate
results in a decrease in the flow velocity. It is likely that a
reduction in friction will improve the flow of material away from
the bottom of the hole, even in situations where bit balling per se
has not occurred.
[0009] Nozzles and fluid courses are designed into the bits for the
purpose of removing material with hydraulic energy. Bit vendors
apply sophisticated computational fluid dynamic models to optimize
these fluid paths, adjusting the number and placement of the
nozzles and the geometry of the spacing between blades of the
bit.
[0010] It is known that in many applications, more hydraulic energy
provides increased drilling rates. However, there are other
factors, such as maximum flow rates, pressure drop across tools,
surface pressure limits, etc., that pose a limit to increasing the
hydraulic energy at the bit. Even with high velocity drilling fluid
jets across some areas of the bit, some other areas have low
velocity and are subject to bit balling. Once cuttings have
attached in one area of the bit, the cuttings accretion process has
been inititated and bit-balling can occur.
[0011] Because of its impact on the well construction process, the
petroleum industry has attempted to mitigate bit balling. At least
one bit manufacturer applies a polymeric coating to the bit
surface. Baker Hughes (U.S. Pat. No. 6,450,271B2), "Surface
Modifications for Rotary Drill Bits," discloses application of low
friction coatings to drill bits. The concept of generic DLC
("Diamond-Like Carbon") and carbon-containing coatings is
disclosed. Another Baker Hughes reference is US Patent Publication
No. 2012/0205162 A1, "Downhole Tools Having Features for Reducing
Balling, Methods of Forming Such Tools, and Methods of Repairing
Such Tools." This reference discloses removable coated materials,
including the use of DLC coatings. This vendor provides examples of
the benefits of a polymeric coated bit in IADC/SPE 74514,
"Innovative Low-Friction Coating Reduces PDC Balling and Doubles
ROP Drilling Shales with WBM." Another vendor, Schlumberger, has
worked with a Norwegian company, Lyng Drilling, to apply a metallic
coating to the bit surface to eliminate bit balling
(http:/www.slb.com/services/drilling/drill_bits/lyng_pdc_bits/antiballing-
_coating.aspx). These references do not disclose the advanced
multi-layer carbon-based coating systems that are disclosed herein
nor the manufacturing adjustments necessary to fabricate such
carbon-based coating systems.
[0012] Reduction of friction is a key requirement in many oil and
gas rotary drilling applications. One method for reducing friction
is improving the lubricity of drilling muds. In industry drilling
operations, attempts have been made to reduce friction through,
mainly, using water and/or oil based mud solutions containing
various types of expensive and often environmentally unfriendly
additives. Diesel and other mineral oils are also often used as
lubricants, but proper disposal of the mud can be expensive.
Certain minerals such as bentonite are known to help reduce
friction between the drill stem assembly and an open borehole.
Other additives include vegetable oils, asphalt, graphite,
detergents and walnut hulls, but each has its own limitations.
Another issue is the fact that the COF increases with increasing
temperature, especially with water-based muds, but also for
oil-based fluids.
[0013] Several references provide documentation that friction
reduction increases drilling rate. For example, SPE 28708,
"Innovative Additives Can Increase the Drilling Rates of
Water-Based Muds" by F. B. Growcock et al. (1994); and SPE 48940,
"Improved Sliding Through Chemistry" by R. G. Bland and W. D.
Halliday (1998).
[0014] Yet another method for reducing drilling friction is to use
a hard facing material on the drill string assembly (also referred
to herein as hardbanding or hardfacing). U.S. Pat. No. 4,665,996,
herein incorporated by reference in its entirety, discloses the use
of hardfacing the principal bearing surface of a drill pipe with an
alloy having the composition of: 50-65% cobalt, 25-35% molybdenum,
1-18% chromium, 2-10% silicon and less than 0.1% carbon for
reducing the friction between the drill string and the casing or
rock. As a result, the torque needed for the rotary drilling
operation, especially directional drilling, is decreased. The
disclosed alloy also provides excellent wear resistance on the
drill string while reducing the wear on the well casing.
Hardbanding may be applied to portions of the drill bit using weld
overlay or thermal spray methods.
[0015] Wear and erosion of the bit body can lead to bit failure.
Presently, one preferred solution to reduce wear is to hardface
portions of the drill bit. In the present application, hardfacing
is applied to steel-body bits at the locations on the bit that have
been subjected to substantial wear. Hardfacing is not typically
applied at locations where bit balling accretions accumulate
because these areas typically do not wear, and the hardfacing
material is not known to have anti-balling properties. Hardfacing
may be applied to both fixed cutter PDC and roller cone bits for
wear resistance.
[0016] U.S. Pat. Nos. 7,182,160, 6,349,779 and 6,056,073 disclose
the designs of grooved segments in drill strings for the purpose of
improving fluid flow in the annulus and reducing contact and
friction with the borehole wall. Previous applications have
disclosed the use of patterned hardfacing areas in friction
reducing coating applications to reduce drilling friction and wear,
for example U.S. Patent Publication No. 2011/0220,415 entitled
"Ultra-Low Friction Coatings for Drill Stem Assemblies."
Need for the Current Disclosure:
[0017] Given the important role of the bit and drilling tools in
the hole making process, there is a need for coatings that have
improved properties with regard to resisting balling, and reducing
friction and wear. Improved coatings to reduce balling and friction
will advantageously demonstrate higher durability relative to prior
art coatings. Modifications to the manufacturing process of
drilling tools will provide the most advantageous implementations
of this technology.
SUMMARY
[0018] The properties of the advanced coatings disclosed herein are
such that the manufacturing process of drilling tools must be
modified to maximize the benefits of such coatings.
[0019] According to one aspect of the present disclosure, an
advantageous method of manufacturing a drilling tool includes:
providing one or more drilling tool components with specified
locations for fitting cutters, inserts, bearings, rollers,
additional non-coated components, or combinations thereof; cleaning
said one or more drilling tool components with specified locations
to remove oil, organic compounds, and/or adsorbates; applying
masking to said cleaned specified locations for fitting cutters,
inserts, bearings, rollers, additional non-coated components or
combinations thereof; applying a multi-layer low friction coating
to said cleaned specified locations; removing the masking from said
cleaned and coated specified locations of said one or more drilling
components; inserting cutters and inserts and assembling moving
parts to the cleaned and coated specified locations of the one or
more drilling tool components; and assembling the one or more
drilling tool components to form a drilling tool. The multi-layer
low friction coating comprises: i) an under layer selected from the
group consisting of CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN,
TiSiCN, TiAlSiN and combinations thereof, wherein the under layer
ranges in thickness from 0.1 to 100 .mu.m, ii) an adhesion
promoting layer selected from the group consisting of Cr, Ti, Si,
W, CrC, TiC, SiC, WC, and combinations thereof, wherein the
adhesion promoting layer ranges in thickness from 0.1 to 50 .mu.m
and is contiguous with a surface of the under layer, and iii) a
functional layer selected from the group consisting of a fullerene
based composite, graphene, a diamond based material,
diamond-like-carbon (DLC), and combinations thereof, wherein the
functional layer ranges from 0.1 to 50 .mu.m and is contiguous with
a surface of the adhesion promoting layer. The adhesion promoting
layer is interposed between the under layer and the functional
layer, and may also provide the added function of toughness
enhancement. The coefficient of friction of the functional layer of
the low friction coating as measured by the block on ring friction
test is less than or equal to 0.15, and the abrasion resistance of
the low friction coating as measured by the modified ASTM G105
abrasion test yields a wear scar depth of less than or equal to 20
.mu.m and a weight loss less than or equal to 0.03 grams.
[0020] These and other features and attributes of the disclosed
methods of making drilling tools with multilayer low friction
coatings will be apparent from the detailed description which
follows, particularly when read in conjunction with the figures
appended hereto.
BRIEF DESCRIPTION OF DRAWINGS
[0021] To assist those of ordinary skill in the relevant art in
making and using the subject matter hereof, reference is made to
the appended drawings, wherein:
[0022] FIG. 1 depicts X-sectional micrographs of test specimens
deposited with different coating architectures after high-sand
CETR-BOR testing wherein the bottom layer constitutes a (ferrous)
substrate, an adhesion promoting (toughness enhancing) CrN layer
separates the top functional layer(s) from the substrate. More
detailed information on the architectures can be found in Table 1
below.
[0023] FIG. 2 illustrates the areas of drilling tools that are
subject to balling with FIG. 2a illustrating balling of the junk
slot of a PDC bit; FIG. 2b showing balling of a junk slot in a
stabilizer blade; and FIG. 2c depicting balling occurring in the
junk slots of a tricone bit and a hole opener.
DEFINITIONS
[0024] "Bottom hole assembly" (BHA) is comprised of one or more
devices, including but not limited to: stabilizers, variable-gauge
stabilizers, back reamers, drill collars, flex drill collars,
rotary steerable tools, roller reamers, shock subs, mud motors,
logging while drilling (LWD) tools, measuring while drilling (MWD)
tools, coring tools, under-reamers, hole openers, centralizers,
turbines, bent housings, bent motors, drilling jars, acceleration
jars, crossover subs, bumper jars, torque reduction tools, float
subs, fishing tools, fishing jars, washover pipe, logging tools,
survey tool subs, non-magnetic counterparts of any of these
devices, and combinations thereof and their associated external
connections.
[0025] "Contiguous" refers to objects which are adjacent to one
another such that they may share a common edge or face.
"Non-contiguous" refers to objects that do not have a common edge
or face because they are offset or displaced from one another. For
example, tool joints are larger diameter cylinders that are
non-contiguous because a smaller diameter cylinder, the drill pipe,
is positioned between the tool joints.
[0026] "Drill collars" are heavy wall pipe in the bottom hole
assembly near the bit. The stiffness of the drill collars help the
bit to drill straight, and the weight of the collars are used to
apply weight to the bit to drill forward.
[0027] "Drill stem" is defined as the entire length of tubular
pipes, comprised of the kelly (if present), the drill pipe, and
drill collars, that make up the drilling assembly from the surface
to the bottom of the hole. The drill stem does not include the
drill bit. In the special case of casing-while-drilling operations,
the casing string that is used to drill into the earth formations
will be considered part of the drill stem.
[0028] "Drill stem assembly" is defined as a combination of a drill
string and bottom hole assembly or coiled tubing and bottom hole
assembly. The drill stem assembly does not include the drill
bit.
[0029] "Drill string" is defined as the column, or string of drill
pipe with attached tool joints, transition pipe between the drill
string and bottom hole assembly including tool joints, heavy weight
drill pipe including tool joints and wear pads that transmits fluid
and rotational power from the top drive or kelly to the drill
collars and the bit. In some references, but not in this document,
the term "drill string" includes both the drill pipe and the drill
collars in the bottomhole assembly.
[0030] "Drilling tool" includes bits, stabilizers, under-reaming
elements, and other devices that are attached to or included in the
drill stem assembly or bottomhole assembly.
[0031] "Shock sub" is a modified drill collar that has a shock
absorbing spring-like element to provide relative axial motion
between the two ends of the shock sub. A shock sub is sometimes
used for drilling very hard formations in which high levels of
axial shocks may occur.
[0032] "Sliding contact" refers to frictional contact between two
bodies in relative motion, whether separated by fluids or solids,
the latter including particles in fluid (bentonite, glass beads,
etc) or devices designed to cause rolling to mitigate friction. A
portion of the contact surface of two bodies in relative motion
will always be in a state of slip, and thus sliding.
[0033] "Tool joint" is a tapered threaded coupling element for pipe
that is usually made of a special steel alloy wherein the pin and
box connections (externally and internally threaded, respectively)
are fixed to either ends of the pipe. Tool joints are commonly used
on drill pipe but may also be used on work strings and other OCTG,
and they may be friction welded to the ends of the pipe.
[0034] "Top drive" is a method and equipment used to rotate the
drill pipe from a drive system located on a trolley that moves up
and down rails attached to the drilling rig mast. Top drive is the
preferred means of operating drill pipe because it facilitates
simultaneous rotation and reciprocation of pipe and circulation of
drilling fluid. In directional drilling operations, there is often
less risk of sticking the pipe when using top drive equipment.
[0035] "Work strings" are jointed pieces of pipe used to perform a
wellbore operation, such as running a logging tool, fishing
materials out of the wellbore, or performing a cement squeeze
job.
[0036] A "coating" is comprised of one or more adjacent layers and
any included interfaces. A coating may be placed on the base
substrate material of a body assembly, on the hardbanding placed on
a base substrate material, or on another coating.
[0037] A "low friction coating" is a coating for which the
coefficient of friction is less than 0.15 under reference
conditions. A typical low friction coating can include one or more
underlayer(s), adhesion promoting layer(s) and functional
layer(s)
[0038] A "layer" is a thickness of a material that may serve a
specific functional purpose such as reduced coefficient of
friction, high stiffness, or mechanical support for overlying
layers or protection of underlying layers.
[0039] A "low friction layer" or "functional layer" is a layer that
provides low friction in a low friction coating. It can also
provide for improved abrasion and wear resistance.
[0040] An "adhesion promoting layer" provides enhanced adhesion
between functional layer(s) and/or underlayer(s) in a multi-layer
coating. It can also provide enhanced toughness.
[0041] An "underlayer" is applied between the outer surface of body
assembly substrate material or hardbanding or buttering layer and
adhesion promoting layer or functional layer or between functional
layer(s) and/or adhesion promoting layer(s) in a multi-layer
coating.
[0042] A "graded layer" is a layer in which at least one
constituent, element, component, or intrinsic property of the layer
changes over the thickness of the layer or some fraction
thereof.
[0043] A "buttering layer" is a layer interposed between the outer
surface of the body assembly substrate material or hardbanding and
a layer, which may be another buttering layer, or a layer
comprising the low friction coating. There may be one or more
buttering layers interposed in such a manner. The buttering layer
can include, but is not limited to, underlayer(s) that comprise the
low friction coating.
[0044] "Hardbanding" is a layer interposed between the outer
surface of the body assembly substrate material and the buttering
layer(s), or one of the layers comprising the low friction coating.
Hardbanding may be utilized in the oil and gas drilling industry to
prevent tool joint and casing wear.
[0045] An "interface" is a transition region from one layer to an
adjacent layer wherein one or more constituent material composition
and/or property value changes from 5% to 95% of the values that
characterize each of the adjacent layers.
[0046] A "graded interface" is an interface that is designed to
have a gradual change of constituent material composition and/or
property value from one layer to the adjacent layer. For example, a
graded interface may be created as a result of gradually stopping
the processing of a first layer while simultaneously gradually
commencing the processing of a second layer.
[0047] A "non-graded interface" is an interface that has a sudden
change of constituent material composition and/or property value
from one layer to the adjacent layer. For example, a non-graded
interface may be created as a result of stopping the processing of
one layer and subsequently commencing the processing of a second
layer.
[0048] (Note: Several of the above definitions are from A
Dictionary for the Petroleum Industry, Third Edition, The
University of Texas at Austin, Petroleum Extension Service,
2001.)
DETAILED DESCRIPTION
[0049] All numerical values within the detailed description and the
claims herein are modified by "about" or "approximately" the
indicated value, and take into account experimental error and
variations that would be expected by a person to having ordinary
skill in the art.
[0050] This disclosure relates to the utilization of Diamond-Like
Carbon (DLC) coating technology on drilling tools to enable faster
drilling by reducing bit balling and bit friction. Cuttings made by
a drill bit during drilling can adhere to the surface of a bit,
particularly in regions that have low flow velocity. Such balling
can occur on bit and drilling tool surfaces where the shear stress
applied by the drilling fluid is insufficient to overcome the
sticking forces to keep the cuttings flowing. Cuttings accumulate
as the initial material hinders the flow of more cuttings and
material builds up or "accretes." This pile-up of material reduces
the bit depth of cut and the overall effectiveness of the bit.
[0051] Placing a diamond-like carbon coating on a drill bit,
including along the fluid courses (and including the "junk slots"),
will increase the overall hydrophobicity of the bit and decrease
the effective coefficient of friction of the bit surface,
minimizing cuttings accumulation and bit balling. Note that this
coefficient of friction is different from the concept of "bit
friction factor" that refers to the amount of bit torque generated
per unit weight on bit, however reducing the sliding friction
coefficient of the bit surface may indeed reduce the torque per
unit weight on bit. This low friction coating on the bit will
reduce the parasitic torque due to the bit surface rubbing against
the rock, resulting in a more effective bit design. Friction
coefficients for a DLC surface rubbing against a rock counterface
material of less than 0.2 may be obtained, compared to 0.35 or more
for a steel-on-rock interface.
[0052] DLC coatings have the following advantages over other types
of coatings: (1) They have excellent adhesion to the bit because
they are deposited in a way which creates chemical bonds at the
bit-coating interface; (2) They are harder than polymeric coatings
and therefore last longer; and (3) When the coatings do eventually
wear, they are abraded away or delaminate in small micron-sized
pieces, which do not risk clogging in the well.
[0053] The disclosed coatings will provide more benefit if the
drilling tool manufacturing process is modified to accommodate DLC
coating properties. For example, depending on the coating applied,
the temperature of the bit or drilling tool should be limited after
the coating has been applied. Additionally, polishing the surface
that will be coated may best be accomplished prior to installation
of cutters or brazed inserts. Also, hardfacing may be applied
generously to the surface of a steel drilling tool, including not
only areas subject to wear but also those areas that may be subject
to balling and require coating durability. Hardfacing provides a
harder substrate for the coating and has been found to be conducive
to longer DLC coating life in laboratory and field tests.
[0054] For these and other reasons to be disclosed herein,
modifications to the process of manufacturing coated drilling tools
will provide the greatest benefit that may be derived from the use
of these coatings.
RELATED APPLICATIONS
[0055] U.S. Pat. No. 8,220,563, herein incorporated by reference in
its entirety, discloses the use of ultra-low friction coatings on
drill stem assemblies used in gas and oil drilling applications.
Other oil and gas well production devices may benefit from the use
of the coatings disclosed herein. A drill stem assembly is one
example of a production device that may benefit from the use of
coatings. The geometry of an operating drill stem assembly is one
example of a class of applications comprising a cylindrical body.
In the case of the drill stem, the actual drill stem assembly is an
inner cylinder that is in sliding contact with the casing or open
hole, an outer cylinder. These devices may have varying radii and
alternatively may be described as comprising multiple contiguous
cylinders of varying radii. As described below, there are several
other instances of cylindrical bodies in oil and gas well
production operations, either in sliding contact due to relative
motion or stationary subject to contact by fluid flowstreams. The
inventive coatings may be used advantageously for each of these
applications by considering the relevant problem to be addressed,
by evaluating the contact or flow problem to be solved to mitigate
friction, wear, corrosion, erosion, or deposits, and by judicious
consideration of how to apply such coatings to the specific devices
for maximum utility and benefit.
[0056] U.S. Pat. No. 8,261,841, herein incorporated by reference in
its entirety, discloses the use of ultra-low friction coatings on
oil and gas well production devices and methods of making and using
such coated devices. In one form, the coated oil and gas well
production device includes an oil and gas well production device
including one or more bodies, and a coating on at least a portion
of the one or more bodies, wherein the coating is chosen from an
amorphous alloy, a heat-treated electroless or electro plated based
nickel-phosphorous composite with a phosphorous content greater
than 12 wt %, graphite, MoS.sub.2, WS.sub.2, a fullerene based
composite, a boride based cermet, a quasicrystalline material, a
diamond based material, diamond-like-carbon (DLC), boron nitride,
and combinations thereof. The coated oil and gas well production
devices may provide for reduced friction, wear, corrosion, erosion,
and deposits for well construction, completion and production of
oil and gas.
[0057] U.S. Pat. No. 8,286,715, herein incorporated by reference in
its entirety, discloses the use of ultra-low friction coatings on
sleeved oil and gas well production devices and methods of making
and using such coated devices. In one form, the coated sleeved oil
and gas well production device includes an oil and gas well
production device including one or more bodies and one or more
sleeves to proximal to the outer or inner surface of the one or
more bodies, and a coating on at least a portion of the inner
sleeve surface, outer sleeve surface, or a combination thereof,
wherein the coating is chosen from an amorphous alloy, a
heat-treated electroless or electro plated based nickel-phosphorous
composite with a phosphorous content greater than 12 wt %,
graphite, MoS2, WS2, a fullerene based composite, a boride based
cermet, a quasicrystalline material, a diamond based material,
diamond-like-carbon (DLC), boron nitride, and combinations thereof.
The coated sleeved oil and gas well production devices may provide
for reduced friction, wear, erosion, corrosion, and deposits for
well construction, completion and production of oil and gas.
[0058] U.S. Patent Publication No. 2011-0220415A1, herein
incorporated by reference in its entirety, discloses drill stem
assemblies with ultra-low friction coatings for subterraneous
drilling operations. In one form, the coated drill stem assemblies
for subterraneous rotary drilling operations include a body
assembly with an exposed outer surface including a drill string
coupled to a bottom hole assembly, a coiled tubing coupled to a
bottom hole assembly, or a casing string coupled to a bottom hole
assembly and an ultra-low friction coating on at least a portion of
the exposed outer surface of the body assembly, hardbanding on at
least a portion of the exposed outer surface of the body assembly,
an ultra-low friction coating on at least a portion of the
hardbanding, wherein the ultra-low friction coating comprises one
or more ultra-low friction layers, and one or more buttering layers
interposed between the hardbanding and the ultra-low friction
coating. The coated drill stem assemblies provide for reduced
friction, vibration (stick-slip and torsional), abrasion, and wear
during straight hole or directional drilling to allow for improved
rates of penetration and enable ultra-extended reach drilling with
existing top drives.
[0059] U.S. Patent Publication No. 2011-0220348A1, herein
incorporated by reference in its entirety, discloses coated oil and
gas well production devices and methods of making and using such
coated devices. In one form, the coated device includes one or more
cylindrical bodies, hardbanding on at least a portion of the
exposed outer surface, exposed inner surface, or a combination of
both exposed outer or inner surface of the one or more cylindrical
bodies, and a coating on at least a portion of the inner surface,
the outer surface, or a combination thereof of the one or more
cylindrical bodies. The coating includes one or more ultra-low
friction layers, and one or more buttering layers interposed
between the hardbanding and the ultra-low friction coating. The
coated oil and gas well production devices may provide for reduced
friction, wear, erosion, corrosion, and deposits for well
construction, completion and production of oil and gas.
[0060] U.S. Patent Publication No. 2011-0203791A1, herein
incorporated by reference in its entirety, discloses coated sleeved
oil and gas well production devices and methods of making and using
such coated sleeved devices. In one form, the coated sleeved oil
and gas well production device includes one or more cylindrical
bodies, one or more sleeves proximal to the outer diameter or inner
diameter of the one or more cylindrical bodies, hardbanding on at
least a portion of the exposed outer surface, exposed inner
surface, or a combination of both exposed outer or inner surface of
the one or more sleeves, and a coating on at least a portion of the
inner sleeve surface, the outer sleeve surface, or a combination
thereof of the one or more sleeves. The coating includes one or
more ultra-low friction layers, and one or more buttering layers
interposed between the hardbanding and the ultra-low friction
coating. The coated sleeved oil and gas well production devices may
provide for reduced friction, wear, erosion, corrosion, and
deposits for well construction, completion and production of oil
and gas.
[0061] U.S. Patent Publication No. 2011-0162751A1, herein
incorporated by reference in its entirety, discloses coated
petrochemical and chemical industry devices and methods of making
and using such coated devices. In one form, the coated
petrochemical and chemical industry device includes a petrochemical
and chemical industry device including one or more bodies, and a
coating on at least a portion of the one or more bodies, wherein
the coating is chosen from an amorphous alloy, a heat-treated
electroless or electro plated based nickel-phosphorous composite
with a phosphorous content greater than 12 wt %, graphite,
MoS.sub.2, WS.sub.2, a fullerene based composite, a boride based
cermet, a quasicrystalline material, a diamond based material,
diamond-like-carbon (DLC), boron nitride, and combinations thereof.
The coated petrochemical and chemical industry devices may provide
for reduced friction, wear, corrosion and other properties required
for superior performance.
[0062] U.S. Provisional Patent Application No. 61/542,501 filed on
Oct. 3, 2011, herein incorporated by reference in its entirety,
discloses methods and systems for vacuum coating the outside
surface of tubular devices for use in oil and gas exploration,
drilling, completions, and production operations for friction
reduction, erosion reduction and corrosion protection. These
methods include embodiments for sealing tubular devices within a
vacuum chamber such that the entire device is not contained within
the chamber. These methods also include embodiments for surface
treating of tubular devices prior to coating. In addition, these
methods include embodiments for vacuum coating of tubular devices
using a multitude of devices, a multitude of vacuum chambers and
various coating source configurations.
[0063] U.S. patent application Ser. No. 13/724,403 filed on Dec.
21, 2012, herein incorporated by reference in its entirety,
discloses low friction coatings with improved abrasion, wear
resistance and methods of making such coatings. In one form, the
coating includes: i) an under layer selected from the group
consisting of CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN,
TiAlSiN and combinations thereof, wherein the under layer ranges in
thickness from 0.1 to 100 .mu.m, ii) an adhesion promoting layer
selected from the group consisting of Cr, Ti, Si, W, CrC, TiC, SiC,
WC, and combinations thereof, wherein the adhesion promoting layer
ranges in thickness from 0.1 to 50 .mu.m and is contiguous with a
surface of the under layer, and iii) a functional layer selected
from the group consisting of a fullerene based composite, a diamond
based material, diamond-like-carbon and combinations thereof,
wherein the functional layer ranges from 0.1 to 50 .mu.m and is
contiguous with a surface of the adhesion promoting layer.
Exemplary Multi-Layer Low Friction Coating Embodiments:
[0064] The Applicants have discovered multi-layer low friction
coatings that yield improved coating durability in severe
abrasive/loading conditions. In a preferred form, these low
friction coatings include a diamond-like-carbon (DLC) as one of the
layers in the coating.
[0065] DLC coatings offer an attractive option to mitigate the
negative effects discussed above, as (a) very low COF values can be
realized (<0.15, and even <0.1), (b) the COF remains largely
stable as a function of temperature, and (c) abrasive wear issues
caused by hard particles such as carbides are greatly reduced. The
typical structure of DLC coatings requires a layer of very hard
amorphous carbon in varying forms of hybridization (i.e. sp2 or
sp3-like character). Typically, with increasing sp3 content, the
DLC layer becomes harder, but may also develop more residual
compressive stress. The hardness and residual stress can be
controlled by varying the sp2/sp3 ratio. Increasing sp2 content
(i.e. graphite-like nature) typically reduces the hardness and the
compressive strength. The sp2/sp3 ratio and overall chemistry can
be varied by controlling various parameters during the deposition
process (e.g. PVD, CVD or PACVD), such as substrate bias, gas
mixture ratio, laser fluence (if applicable), substrate, deposition
temperature, hydrogenation level, use of dopants in the DLC layer
(metallic and/or non-metallic) etc. However, the reduction of
residual stress in the DLC layer is generally accompanied by a
reduction in hardness of the DLC (and reduction in sp3 content).
While highly sp3-like DLC coatings can reach very high hardness
values (.about.4500-6000 Hv), these coatings exhibit compressive
stresses >>1 GPa, detrimental to durability in applications
describe above.
[0066] Hence, there is a need for novel DLC compositions with
varying sp2/sp3 ratios, aimed at providing higher hardness values
(in the range of 1700-5500 Hv) for use in extended reach rotary
drilling devices, coated oil and gas well production devices
(sleeved and unsleeved) and petrochemical and chemical industry
equipment and devices. Hardness values lower than .about.1500 Hv
are considered unsuitable for the envisioned application space, as
the abrasive nature of relatively hard particles (e.g. sand,
components of oil-based drilling mud etc.) is expected to quickly
wear out the DLC coating.
[0067] While typical DLC coatings do offer improved hardness (in
the range of 2500 Hv), there is a need to consider harder versions
(Hv>3000) while managing residual stress for optimal coating
thickness buildup. In addition, there is a need to minimize the
plastic deformation of underlying substrate in the presence of
abrasive, 3-body contact scenarios.
[0068] Durability of Diamond-like Carbon (DLC) coatings under
three-body contact scenarios (i.e., in the presence of abrasive
particles) is limited by overall abrasion resistance of the coating
and spallation/delamination of coating that can be instigated by
plastic deformation of underneath substrate due to creation of high
local stresses. For DLC coatings to have enhanced durability in
severe loading/abrasive environments, techniques to suppress
existing failure modes to improve overall durability are
needed.
[0069] In one form, a multi-layer low friction coating of the
present disclosure includes an under layer that would be contiguous
with a surface of a substrate for coating, an adhesion promoting
and toughness enhancing layer contiguous with a surface of the
under layer, and a functional layer contiguous with a surface of
the adhesion promoting layer. Hence, the adhesion promoting layer
is interposed between the under layer and the functional layer. The
functional layer is the outermost exposed layer of the multi-layer
low friction coating.
[0070] The surface of the substrate for coating may be made from a
variety of different materials. Non-limiting exemplary substrates
for coating include steel, stainless steel, hardbanding, an iron
alloy, an aluminum based alloy, a titanium based alloy, ceramics
and a nickel based alloy. Non-limiting exemplary hardbanding
materials include cermet based materials, metal matrix composites,
nanocrystalline metallic alloys, amorphous alloys and hard metallic
alloys. Other non-limiting exemplary types of hardbanding include
carbides, nitrides, borides, and oxides of elemental tungsten,
titanium, niobium, molybdenum, iron, chromium, and silicon
dispersed within a metallic alloy matrix. Such hardbanding may be
deposited by weld overlay, thermal spraying or laser/electron beam
cladding. The thickness of hardbanding layer may range from several
orders of magnitude times that of or equal to the thickness of the
outer coating layer. Non-limiting exemplary hardbanding thicknesses
are 1 mm, 2 mm, and 3 mm proud above the surface of the drill stem
assembly. The hardbanding surface may have a patterned design to
reduce entrainment of abrasive particles that contribute to wear.
The multi-layer low friction coatings disclosed herein may be
deposited on top of the hardbanding pattern. The hardbanding
pattern may include both recessed and raised regions and the
thickness variation in the hardbanding can be as much as its total
thickness.
[0071] The multi-layer low friction coatings of the present
disclosure may be applied to a portion of the surface of a device
chosen from the following exemplary non-limiting types: a drill bit
or a drilling tool for subterraneous rotary drilling, a drill stem
assembly for subterraneous rotary drilling, and stabilizers and
centralizers. In addition, the multi-layer low friction coatings of
the present disclosure may be applied to a portion of the surface
of devices described in the definition section of the present
disclosure.
[0072] The under layer of the low friction coating disclosed herein
may be made from a variety of different materials, including, but
not limited to, CrN, TiN, TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN.
TiAlSiN and combinations thereof. The thickness of the under layer
may range from 0.1 to 100 .mu.m, or 1 to 75 .mu.m, or 2 to 50
.mu.m, or 3 to 35 .mu.m or 5 to 25 .mu.m. The under layer may have
a hardness that ranges from 800 to 4000 VHN, or 1000 to 3500 VHN,
or 1200 to 3000 VHN, or 1500 to 2500 VHN, or 1800 to 2200 VHN.
[0073] The adhesion promoting layer of the low friction coating
disclosed herein not only improves the adhesion between the under
layer and the functional layer, but also enhances the overall
toughness of the coating. For this reason, it may also be referred
to herein as a toughness enhancing layer. The adhesion promoting
layer of the low friction coating disclosed herein may be made from
a variety of different materials, including, but not limited to,
Cr, Ti, Si, W, CrC, TiC, SiC, WC, and combinations thereof. The
thickness of the adhesion promoting layer may range from 0 to 60
.mu.m, or 0.01 to 50 .mu.m, or 0.1 to 25 .mu.m, or 0.2 to 20 .mu.m,
or 0.3 to 15 .mu.m, or 0.5 to 10 .mu.m. The adhesion promoting
layer may have a hardness that ranges from 200 to 2500 VHN, or 500
to 2000 VHN, or 800 to 1700 VHN, or 1000 to 1500 VHN. There is also
generally a compositional gradient or transition at the interface
of the under layer and the adhesion promoting layer, which may
range in thickness from 0.01 to 10 .mu.m, or 0.05 to 9 .mu.m, or
0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0074] The functional layer of the low friction coating disclosed
herein may be made from a variety of different materials,
including, but not limited to, a fullerene based composite,
graphene, a diamond based material, diamond-like-carbon (DLC) and
combinations thereof. Non-limiting exemplary diamond based
materials include chemical vapor deposited (CVD) diamond or
polycrystalline diamond compact (PDC). The functional layer of the
low friction coating disclosed herein is advantageously
diamond-like-carbon (DLC) coating, and more particularly the DLC
coating may be chosen from tetrahedral amorphous carbon (ta-C),
tetrahedral amorphous hydrogenated carbon (ta-C:H), diamond-like
hydrogenated carbon (DLCH), polymer-like hydrogenated carbon
(PLCH), graphite-like hydrogenated carbon (GLCH), silicon
containing diamond-like-carbon (Si-DLC), titanium containing
diamond-like-carbon (Ti-DLC), chromium containing
diamond-like-carbon (Cr-DLC), metal containing diamond-like-carbon
(Me-DLC), oxygen containing diamond-like-carbon (O-DLC), nitrogen
containing diamond-like-carbon (N-DLC), boron containing
diamond-like-carbon (B-DLC), fluorinated diamond-like-carbon
(F-DLC), sulfur-containing diamond-like carbon (S-DLC), and
combinations thereof. The functional layer may be graded for
improved durability, friction reduction, adhesion, and mechanical
performance. The thickness of the functional layer may range from
0.1 to 50 .mu.m, or 0.2 to 40 .mu.m, or 0.5 to 25 .mu.m, or 1 to 20
.mu.m, or 2 to 15 .mu.m, or 5 to 10 .mu.m. The functional layer may
have a Vickers hardness that ranges from 1000 to 7500 VHN, or 1500
to 7000 VHN, or 2000 to 6500 VHN, or 2200 to 6000 VHN, or 2500 to
5500 VHN, or 3000 to 5000 VHN. The functional layer may have a
surface roughness that ranges from 0.01 .mu.m to 1.0 .mu.m Ra, or
0.03 .mu.m to 0.8 .mu.m Ra, or 0.05 .mu.m to 0.5 .mu.m Ra, or 0.07
.mu.m to 0.3 .mu.m Ra, or 0.1 .mu.m to 0.2 .mu.m Ra. There is also
generally a compositional gradient or transition at the interface
of the adhesion promoting layer and the functional layer, which may
range in thickness from 0.01 to 10 .mu.m, or 0.05 to 9 .mu.m, or
0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0075] In another form of the present disclosure, the multi-layer
low friction coating including an under layer contiguous with a
surface of a substrate for coating, an adhesion promoting layer
contiguous with a surface of the under layer, and a functional
layer contiguous with a surface of the adhesion promoting layer may
further include a second adhesion promoting layer that is
contiguous with a surface of the functional layer, and a second
functional layer that is contiguous with a surface of the second
adhesion promoting layer. Hence, the second adhesion promoting
layer is interposed between the functional layer described above
and a second functional layer. The second functional layer is the
outermost exposed layer of the multi-layer low friction
coating.
[0076] The second adhesion promoting layer may be made from the
following non-limiting exemplary materials: Cr, Ti, Si, W, CrC,
TiC, SiC, WC, and combinations thereof. The thickness of the second
adhesion promoting layer may range from 0 to 60 .mu.m, or 0.1 to 50
.mu.m, or 1 to 25 .mu.m, or 2 to 20 .mu.m, or 3 to 15 .mu.m, or 5
to 10 .mu.m. The second adhesion promoting layer may have a Vickers
hardness that ranges from 200 to 2500 VHN, or 500 to 2000 VHN, or
800 to 1700 VHN, or 1000 to 1500 VHN. There is also generally a
compositional gradient or transition at the interface of the
functional layer and the second adhesion promoting layer, which may
range in thickness from 0.01 to 10 .mu.m, or 0.05 to 9 .mu.m, or
0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0077] The second functional layer may also be made from a variety
of different materials, including, but not limited to, a fullerene
based composite, graphene, a diamond based material,
diamond-like-carbon (DLC) and combinations thereof. Non-limiting
exemplary diamond based materials include chemical vapor deposited
(CVD) diamond or polycrystalline diamond compact (PDC).
Non-limiting exemplary diamond-like-carbon include ta-C, ta-C:H,
DLCH, PLCH, GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and
combinations thereof. The thickness of the second functional layer
may range from 0.1 to 50 .mu.m, or 0.2 to 40 .mu.m, or 0.5 to 25
.mu.m, or 1 to 20 .mu.m, or 2 to 15 .mu.m, or 5 to 10 .mu.m. The
second functional layer may have a hardness that ranges from 1000
to 7500 VHN, or 1500 to 7000 VHN, or 2000 to 6500 VHN, or 2500 to
6000 VHN, or 3000 to 5500 VHN, or 3500 to 5000 VHN. The second
functional layer may have a surface roughness that ranges from 0.01
.mu.m to 1.0 .mu.m Ra, or 0.03 .mu.m to 0.8 .mu.m Ra, or 0.05 .mu.m
to 0.5 .mu.m Ra, or 0.07 .mu.m to 0.3 .mu.m Ra, or 0.1 .mu.m to 0.2
.mu.m Ra. There is also generally a compositional gradient or
transition at the interface of the second adhesion promoting layer
and the second functional layer, which may range in thickness from
0.01 to 10 .mu.m, or 0.05 to 9 .mu.m, or 0.1 to 8 .mu.m, or 0.5 to
5.
[0078] The multi-layer low friction coating including a second
adhesion promoting layer and a second functional layer may also
optionally include a second under layer interposed between the
functional layer and the second adhesion promoting layer. The
second under layer of the low friction coating disclosed herein may
be made from a variety of different materials, including, but not
limited to, CrN, TiN. TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN,
TiAlSiN and combinations thereof. The thickness of the second under
layer may range from 0.1 to 100 .mu.m, or 2 to 75 .mu.m, or 2 to 75
.mu.m, or 3 to 50 .mu.m, or 5 to 35 .mu.m, or 10 to 25 .mu.m. The
second under layer may have a hardness that ranges from 800 to 3500
VHN, or 1000 to 3300 VHN, or 1200 to 3000 VHN, or 1500 to 2500 VHN,
or 1800 to 2200 VHN.
[0079] In yet another form of the present disclosure, the
multi-layer low friction coating including an under layer
contiguous with a surface of a substrate for coating, an adhesion
promoting layer contiguous with a surface of the under layer, and a
functional layer contiguous with a surface of the adhesion
promoting layer may further include from 1 to 100 series of
incremental coating layers, wherein each series of incremental
coating layers includes a combination of an incremental adhesion
promoting layer, an incremental functional layer and an optional
incremental under layer, wherein the each series of incremental
coating layers is configured as follows: A) the optional
incremental under layer contiguous with a surface of the functional
layer and the incremental adhesion promoting layer; wherein the
optional incremental under layer is interposed between the
functional layer and the incremental adhesion promoting layer; B)
the incremental adhesion promoting layer contiguous with a surface
of the functional layer or optional incremental under layer, and
the incremental functional layer; and the incremental adhesion
promoting layer is interposed between the functional layer and the
incremental functional layer or between the optional incremental
under layer and the incremental functional layer; and C) the
incremental functional layer is contiguous with a surface of the
incremental adhesion promoting layer.
[0080] The optional incremental under layer of the low friction
coating disclosed herein may be made from a variety of different
materials, including, but not limited to, CrN, TiN, TiAlN, TiAlVN,
TiAlVCN, TiSiN, TiSiCN, TiAlSiN and combinations thereof. The
thickness of the optional incremental under layer may range from
0.1 to 100 .mu.m, or 2 to 75 .mu.m, or 2 to 75 .mu.m, or 3 to 50
.mu.m, or 5 to 35 .mu.m, or 10 to 25 .mu.m. The optional
incremental under layer may have a hardness that ranges from 800 to
3500 VHN, or 1000 to 3300 VHN, or 1200 to 3000 VHN, or 1500 to 2500
VHN, or 1800 to 2200 VHN.
[0081] The incremental adhesion promoting layer may be made from
the following non-limiting exemplary materials: Cr, Ti, Si, W, CrC,
TiC, SiC, WC, and combinations thereof. The thickness of the
incremental adhesion promoting layer may range from 0 to 60 .mu.m,
or 0.1 to 50 .mu.m, or 1 to 25 .mu.m, or 2 to 20 .mu.m, or 3 to 15
.mu.m, or 5 to 10 p.m. The incremental adhesion promoting layer may
have a hardness that ranges from 200 to 2500 VHN, or 500 to 2000
VHN, or 800 to 1700 VHN, or 1000 to 1500 VHN. There is also
generally a compositional gradient or transition at the interface
of the optional incremental under layer and the incremental
adhesion promoting layer, which may range in thickness from 0.01 to
10 .mu.m, or 0.05 to 9 .mu.m, or 0.1 to 8 .mu.m, or 0.5 to 5
.mu.m.
[0082] The incremental functional layer may be made from a variety
of different materials, including, but not limited to a fullerene
based composite, graphene, a diamond based material,
diamond-like-carbon (DLC) and combinations thereof. Non-limiting
exemplary diamond based materials include chemical vapor deposited
(CVD) diamond or polycrystalline diamond compact (PDC).
Non-limiting exemplary diamond-like-carbon include ta-C, ta-C:H,
DLCH, PLCH, GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and
combinations thereof. The thickness of the incremental functional
layer may range from 0.1 to 50 .mu.m, or 0.2 to 40 .mu.m, or 0.5 to
25 .mu.m, or 1 to 20 .mu.m, or 2 to 15 .mu.m, or 5 to 10 .mu.m. The
incremental functional layer may have a hardness that ranges from
1000 to 7500 VHN, or 1500 to 7000 VHN, or 2000 to 6500 VHN, or 2200
to 6000 VHN, or 2500 to 5500 VHN, or 3000 to 5000 VHN. The
incremental functional layer may have a surface roughness that
ranges from 0.01 .mu.m to 1.0 .mu.m Ra, or 0.03 .mu.m to 0.8 .mu.m
Ra, or 0.05 .mu.m to 0.5 .mu.m Ra, or 0.07 .mu.m to 0.3 .mu.m Ra,
or 0.1 .mu.m to 0.2 .mu.m Ra. There is also generally a
compositional gradient or transition at the interface of the
incremental adhesion promoting layer and the incremental functional
layer, which may range in thickness from 0.01 to 10 .mu.m, or 0.05
to 9 .mu.m, or 0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0083] The total thickness of the multi-layered low friction
coatings of the present disclosure may range from 0.5 to 5000
microns. The lower limit of the total multi-layered coating
thickness may be 0.5, 0.7, 1.0, 3.0, 5.0, 7.0, 10.0, 15.0, or 20.0
microns in thickness. The upper limit of the total multi-layered
coating thickness may be 25, 50, 75, 100, 200, 500, 1000, 3000,
5000 microns in thickness.
[0084] The multi-layer low friction coatings of the present
disclosure yield a coefficient of friction of the functional layer
of the low friction coating as measured by the block on ring
friction test is less than or equal to 0.15, or less than or equal
to 0.12, or less than or equal to 0.10, or less than or equal to
0.08. The friction force may be calculated as follows: Friction
Force=Normal Force.times.Coefficient of Friction. The multi-layer
low friction coating of the present disclosure yields a counterface
wear scar depth as measured by the block on ring friction test of
less than or equal to 500 .mu.m, or less than or equal to 300
.mu.m, or less than or equal to 100 .mu.m, or less than or equal to
50 .mu.m.
[0085] The multi-layer low friction coatings of the present
disclosure also yield an unexpected improvement in abrasion
resistance. The modified ASTM G105 abrasion test may be used to
measure the abrasion resistance. In particular, the multi-layer low
friction coatings of the present disclosure yield an abrasion
resistance as measured by the modified ASTM G105 abrasion test for
wear scar depth and weight loss that is at least 5 times lower, or
at least 4 times lower, or at least 2 times lower than a single
layer coating of the same functional layer. The multi-layer low
friction coatings of the present disclosure yield a wear scar depth
via the modified ASTM G105 abrasion test of less than or equal to
20 .mu.m, or less than or equal to 15 .mu.m, or less than or equal
to 10 .mu.m, or less than or equal to 5 .mu.m, or less than or
equal to 2 .mu.m. The multi-layer low friction coatings of the
present disclosure yield a weight loss via the modified ASTM G105
abrasion test of less than or equal to 0.03 grams, or less than or
equal to 0.02 grams, or less than or equal to 0.01 grams, or less
than or equal to 0.005 grams, or less than or equal to 0.004 grams,
or less than or equal to 0.001 grams.
Exemplary Method of Making Multi-layer Low Friction Coatings
Embodiments:
[0086] The multi-layer low friction coatings of the present
disclosure may be made by a variety of process techniques. In one
exemplary form, a method of making a low friction coating includes
the following steps: i) providing a substrate for coating, ii)
depositing on a surface of the substrate an under layer, iii)
depositing on the surface of the under layer an adhesion promoting
layer is contiguous with a surface of the under layer, iv)
depositing on the surface of the adhesion promoting layer a
functional layer that is contiguous with a surface of the adhesion
promoting layer.
[0087] The under layer of the method of making a low friction
coating disclosed herein may be made from a variety of different
materials, including, but not limited to, CrN, TiN, TiAlN, TiAlVN,
TiAlVCN, TiSiN, TiSiCN, TiAlSiN and combinations thereof. The
thickness of the under layer may range from 0.1 to to 100 .mu.m, or
2 to 75 .mu.m, or 2 to 75 .mu.m, or 3 to 50 .mu.m, or 5 to 35
.mu.m, or 10 to 25 .mu.m. The under layer may have a hardness that
ranges from 800 to 3500 VHN, or 1000 to 3300 VHN, or 1200 to 3000
VHN, or 1500 to 2500 VHN, or 1800 to 2200 VHN.
[0088] The adhesion promoting layer of the method of making a low
friction coating disclosed herein not only improves the adhesion
between the under layer and the functional layer, but also improves
the toughness of the coating. For this reason, it may also be
referred to herein as a toughness enhancing layer. The adhesion
promoting layer of the low friction coating disclosed herein may be
made from a variety of different materials, including, but not
limited to, Cr, Ti, Si, W, CrC, TiC, SiC, WC, and combinations
thereof. The thickness of the adhesion promoting layer may range
from 0 to 60 .mu.m, or 0.1 to 50 .mu.m, or 1 to 25 .mu.m, or 2 to
20 .mu.m, or 3 to 15 .mu.m, or 5 to 10 .mu.m. The adhesion
promoting layer may have a hardness that ranges from 200 to 2500
VHN, or 500 to 2000 VHN, or 800 to 1700 VHN, or 1000 to 1500 VHN.
There is also generally a compositional gradient or transition at
the interface of the under layer and the adhesion promoting layer,
which may range in thickness from 0.01 to 10 .mu.m, or 0.05 to 9
.mu.m, or 0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0089] The functional layer of the method of making a low friction
coating disclosed herein may be made from a variety of different
materials, including, but not limited to, a fullerene based
composite, graphene, a diamond based material, diamond-like-carbon
(DLC) and combinations thereof. Non-limiting exemplary diamond
based materials include chemical vapor deposited (CVD) diamond or
polycrystalline diamond compact (PDC). Non-limiting exemplary
diamond-like-carbon include ta-C, ta-C:H, DLCH, PLCH, GLCH, Si-DLC,
N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and combinations thereof. The
thickness of the functional layer may range from 0.1 to 50 .mu.m,
or 0.2 to 40 .mu.m, or 0.5 to 25 .mu.m, or 1 to 20 .mu.m, or 2 to
15 .mu.m, or 5 to 10 .mu.m. The functional layer may have a
hardness that ranges from 1000 to 7500 VHN, or 1500 to 7000 VHN, or
2000 to 6500 VHN, or 2200 to 6000 VHN, or 2500 to 5500 VHN, or 3000
to 5000 VHN. The functional layer may have a surface roughness that
ranges from 0.01 .mu.m to 1.0 .mu.m Ra, or 0.03 .mu.m to 0.8 .mu.m
Ra, or 0.05 .mu.m to 0.5 .mu.m Ra, or 0.07 .mu.m to 0.3 .mu.m Ra,
or 0.1 .mu.m to 0.2 .mu.m Ra. There is also generally a
compositional gradient or transition at the interface of the
adhesion promoting layer and the functional layer, which may range
in thickness from 0.01 to 10 .mu.m, or 0.05 to 9 .mu.m, or 0.1 to 8
.mu.m, or 0.5 to 5 .mu.m.
[0090] The method of making a low friction coating described above
may further include depositing additional layers of adhesion
promoting layer(s), functional layer(s) and optional under layer(s)
(between functional layer(s) and adhesion promoting layer(s)) to
further enhance the abrasion resistance, coefficient of friction
and other properties of the multi-layer low friction coating. In
another exemplary form, the method of making a low friction coating
including an under layer contiguous with a surface of a substrate
for coating, an adhesion promoting layer contiguous with a surface
of the under layer, and a functional layer contiguous with a
surface of the adhesion promoting layer may further include the
step of depositing from 1 to 100 series of incremental coating
layers, wherein each series of incremental coating layers includes
a combination of an incremental adhesion promoting layer, an
incremental functional layer and an optional incremental under
layer, wherein the each series of incremental coating layers is
configured as follows: A) the optional incremental under layer
contiguous with a surface of the functional layer and the
incremental adhesion promoting layer; wherein the optional
incremental under layer is interposed between the functional layer
and the incremental adhesion promoting layer; B) the incremental
adhesion promoting layer contiguous with a surface of the
functional layer or optional incremental under layer, and the
incremental functional layer; and the incremental adhesion
promoting layer is interposed between the functional layer and the
incremental functional layer or between the optional incremental
under layer and the incremental functional layer; and C) the
incremental functional layer is contiguous with a surface of the
incremental adhesion promoting layer.
[0091] The optional incremental under layer of the method of making
a low friction coating disclosed herein may be made from a variety
of different materials, including, but not limited to, CrN, TiN,
TiAlN, TiAlVN, TiAlVCN, TiSiN, TiSiCN, TiAlSiN and combinations
thereof. The thickness of the optional incremental under layer may
range from 0.1 to 100 .mu.m, or 2 to 75 .mu.m, or 2 to 75 .mu.m, or
3 to 50 .mu.m, or 5 to 35 .mu.m, or 10 to 25 .mu.m. The optional
incremental under layer may have a hardness that ranges from 800 to
3500 VHN, or 1000 to 3300 VHN, or 1200 to 3000 VHN, or 1500 to 2500
VHN, or 1800 to 2200 VHN.
[0092] The incremental adhesion promoting layer of the method of
making a low friction coating disclosed herein may be made from the
following non-limiting exemplary materials: Cr, Ti, Si, W, CrC,
TiC, SiC, WC, and combinations thereof. The thickness of the
incremental adhesion promoting layer may range from 0 to 60 .mu.m,
or 0.1 to 50 .mu.m, or 1 to 25 .mu.m, or 2 to 20 .mu.m, or 3 to 15
.mu.m, or 5 to 10 .mu.m. The incremental adhesion promoting layer
may have a hardness that ranges from 200 to 2500 VHN, or 500 to
2000 VHN, or 800 to 1700 VHN, or 1000 to 1500 VHN. There is also
generally a compositional gradient or transition at the interface
of the optional incremental under layer and the incremental
adhesion promoting layer, which may range in thickness from 0.01 to
10 .mu.m, or 0.05 to 9 .mu.m, or 0.1 to 8 .mu.m, or 0.5 to 5
.mu.m.
[0093] The incremental functional layer of the method of making a
low friction coating disclosed herein may be made from a variety of
different materials, including, but not limited to, a fullerene
based composite, graphene, a diamond based material,
diamond-like-carbon (DLC) and combinations thereof. Non-limiting
exemplary diamond based materials include chemical vapor deposited
(CVD) diamond or polycrystalline diamond compact (PDC).
Non-limiting exemplary diamond-like-carbon include ta-C, ta-C:H,
DLCH, PLCH, GLCH, Si-DLC, N-DLC, O-DLC, B-DLC, Me-DLC, F-DLC and
combinations thereof. The thickness of the incremental functional
layer may range from 0.1 to 50 .mu.m, or 0.2 to 40 .mu.m, or 0.5 to
25 .mu.m, or 1 to 20 .mu.m, or 2 to 15 .mu.m, or 5 to 10 .mu.m. The
incremental functional layer may have a hardness that ranges from
1000 to 7500 VHN, or 1500 to 7000 VHN, or 2000 to 6500 VHN, or 2200
to 6000 VHN, or 2500 to 5500 VHN, or 3000 to 5000 VHN. The
incremental functional layer may have a surface roughness that
ranges from 0.01 .mu.m to 1.0 .mu.m Ra, or 0.03 .mu.m to 0.8 .mu.m
Ra, or 0.05 .mu.m to 0.5 .mu.m Ra, or 0.07 .mu.m to 0.3 .mu.m Ra,
or 0.1 .mu.m to 0.2 .mu.m Ra. There is also generally a
compositional gradient or transition at the interface of the
incremental adhesion promoting layer and the incremental functional
layer, which may range in thickness from 0.01 to 10 .mu.m, or 0.05
to 9 .mu.m, or 0.1 to 8 .mu.m, or 0.5 to 5 .mu.m.
[0094] The method of making multi-layer low friction coatings of
the present disclosure yield a coefficient of friction of the
functional layer of the low friction coating as measured by the
block on ring friction test is less than or equal to 0.15, or less
than or equal to 0.12, or less than or equal to 0.10, or less than
or equal to 0.08. The multi-layer low friction coating of the
present disclosure yields a counterface wear scar depth as measured
by the block on ring friction test of less than or equal to 500
.mu.m, or less than or equal to 300 .mu.m, or less than or equal to
100 .mu.m, or less than or equal to 50 .mu.m.
[0095] The method of making low friction coatings of the present
disclosure also yields an unexpected improvement in abrasion
resistance. The modified ASTM G105 abrasion test may be used to
measure the abrasion resistance. In particular, the multi-layer low
friction coatings of the present disclosure yield an abrasion
resistance as measured by the modified ASTM G105 abrasion test for
wear scar depth and weight loss that is at least 5 times lower, or
at least 4 times lower, or at least 2 times lower than a single
layer coating of the same functional layer. The multi-layer low
friction coatings of the present disclosure yield a wear scar depth
via the modified ASTM G105 abrasion test of less than or equal to
20 .mu.m, or less than or equal to 15 .mu.m, or less than or equal
to 10 .mu.m, or less than or equal to 5 .mu.m, or less than or
equal to 2 .mu.m. The multi-layer low friction coatings of the
present disclosure yield a weight loss via the modified ASTM G105
abrasion test of less than or equal to 0.03 grams, or less than or
equal to 0.02 grams, or less than or equal to 0.01 grams, or less
than or equal to 0.005 grams, or less than or equal to 0.004 grams,
or less than or equal to 0.001 grams.
[0096] For the method of making low friction coatings of the
present disclosure, the steps of depositing the under layer(s), the
adhesion promoting layer(s) and/or the functional layer(s) may be
chosen from the following non-limiting exemplary methods: physical
vapor deposition, plasma assisted chemical vapor deposition, and
chemical vapor deposition. Non-limiting exemplary physical vapor
deposition coating methods are magnetron sputtering, ion beam
assisted deposition, cathodic arc deposition and pulsed laser
deposition.
[0097] The method of making low friction coatings of the present
disclosure may further include the step of post-processing step the
outermost functional layer to achieve a surface roughness between
0.01 to 1.0 .mu.m Ra, or 0.03 .mu.m to 0.8 .mu.m Ra, or 0.05 .mu.m
to 0.5 .mu.m Ra, or 0.07 .mu.m to 0.3 .mu.m Ra, or 0.1 .mu.m to 0.2
.mu.m Ra. Non-limiting exemplary post-processing steps may include
mechanical polishing, chemical polishing, depositing of smoothening
layers, an ultra-fine superpolishing process, a tribochemical
polishing process, an electrochemical polishing process, and
combinations thereof.
[0098] The method of making low friction coatings of the present
disclosure may be applied to the surface of various substrates for
coating. Non-limiting exemplary substrates for the coating methods
disclosed include steel, stainless steel, hardbanding, an iron
alloy, an aluminum based alloy, a titanium based alloy, ceramics
and a nickel based alloy. Non-limiting exemplary hardbanding
materials include cermet based materials, metal matrix composites,
nanocrystalline metallic alloys, amorphous alloys and hard metallic
alloys. Other non-limiting exemplary types of hardbanding include
carbides, nitrides, borides, and oxides of elemental tungsten,
titanium, niobium, molybdenum, iron, chromium, and silicon
dispersed within a metallic alloy matrix. Such hardbanding may be
deposited by weld overlay, thermal spraying or laser/electron beam
cladding. The thickness of hardbanding layer may range from several
orders of magnitude times that of or equal to the thickness of the
outer coating layer. Non-limiting exemplary hardbanding thicknesses
are 1 mm, 2 mm, and 3 mm proud above the surface of the drill stem
assembly. The hardbanding surface may have a patterned design to
reduce entrainment of abrasive particles that contribute to wear.
The multi-layer low friction coatings disclosed herein may be
deposited on top of the hardbanding pattern. The hardbanding
pattern may include both recessed and raised regions and the
thickness variation in the hardbanding can be as much as its total
thickness.
[0099] The method of making low friction coatings of the present
disclosure may be applied to a portion of the surface of a device
chosen from the following exemplary non-limiting types: a drill bit
or a drilling tool for subterraneous rotary drilling, a drill stem
assembly for subterraneous rotary drilling, and stabilizers and
centralizers. In addition, the multi-layer low friction coating
methods of the present disclosure may be applied to a portion of
the surface of devices described in the definition section of the
present disclosure.
Exemplary Method of Using Multi-layer Low Friction Coatings
Embodiments:
[0100] The multi-layer low friction coatings disclosed herein may
be applied to a portion of the surface of a device selected from
the group consisting of a drill bit or a drilling tool for
subterraneous rotary drilling, a drill stem assembly for
subterraneous rotary drilling, and stabilizers and
centralizers.
[0101] More particularly, the multi-layer low friction coatings
disclosed herein may be used to improve the performance of drilling
tools, particularly a drilling head for drilling in formations
containing clay and similar substances. The present disclosure
utilizes the low surface energy novel materials or coating systems
to provide thermodynamically low energy surfaces, e.g., non-water
wetting surface for bottom hole components. The multi-layer low
friction coatings disclosed herein are suitable for oil and gas
drilling in gumbo-prone areas, such as in deep shale drilling with
high clay contents using water-based muds (abbreviated herein as
WBM) to prevent drill bit and bottom hole assembly component
balling.
[0102] Furthermore, the multi-layer low friction coatings disclosed
herein when applied to the drill string assembly can simultaneously
reduce contact friction, bit balling and reduce wear while not
compromising the durability and mechanical integrity of casing in
the cased hole situation. Thus, the multi-layer low friction
coatings disclosed herein are "casing friendly" in that they do not
degrade the life or functionality of the casing. The multi-layer
low friction coatings disclosed herein are also characterized by
low or no sensitivity to velocity weakening friction behavior.
Thus, the drill stem assemblies provided with the multi-layer low
friction coatings disclosed herein provide low friction surfaces
with advantages in both mitigating stick-slip vibrations and
reducing parasitic torque to further enable ultra-extended reach
drilling.
[0103] The multi-layer low friction coatings disclosed herein for
drill stem assemblies thus provide for the following exemplary
non-limiting advantages: i) mitigating stick-slip vibrations, ii)
reducing torque and drag for extending the reach of extended reach
wells, and iii) mitigating drill bit and other bottom hole
component balling. These three advantages together with minimizing
the parasitic torque may lead to significant improvements in
drilling rate of penetration as well as durability of downhole
drilling equipment, thereby also contributing to reduced
non-productive time (abbreviated herein as NPT). The multi-layer
low friction coatings disclosed herein not only reduce friction,
but also withstand the aggressive downhole drilling environments
requiring chemical stability, corrosion resistance, impact
resistance, durability against wear, erosion and mechanical
integrity (coating-substrate interface strength). The multi-layer
low friction coatings disclosed herein are also amenable for
application to complex shapes without damaging the substrate
properties. Moreover, the multi-layer low friction coatings
disclosed herein also provide low energy surfaces necessary to
provide resistance to balling of bottom hole components.
[0104] The body assembly or the coated drill stem assembly may
include hardbanding on at least a portion of the exposed outer
surface to provide enhanced wear resistance and durability. Drill
stem assemblies experience significant wear at the hardbanded
regions since these are primary contact points between drill stem
and casing or open borehole. The wear can be exacerbated by
abrasive sand and rock particles becoming entrained in the
interface and abrading the surfaces. The coatings on the coated
drill stem assembly disclosed herein show high hardness properties
to help mitigate abrasive wear. Using hardbanding that has a
surface with a patterned design may promote the flow of abrasive
particles past the coated hardbanded region and reduce the amount
of wear and damage to the coating and hardbanded portion of the
component. Using coatings in conjunction with patterned hardbanding
will further reduce wear due to abrasive particles.
[0105] Therefore, another aspect of the disclosure is the use of
multi-layer low friction coatings on a hardbanding on at least a
portion of the exposed outer surface of the body assembly, where
the hardbanding surface has a patterned design that reduces
entrainment of abrasive particles that contribute to wear. During
drilling, abrasive sand and other rock particles suspended in
drilling fluid can travel into the interface between the body
assembly or drill string assembly and casing or open borehole.
These abrasive particles, once entrained into this interface,
contribute to the accelerated wear of the body assembly, drill
string assembly, and casing. There is a need to extend equipment
lifetime to maximize drilling and economic efficiency. Since
hardbanding that is made proud above the surface of the body
assembly or drill string assembly makes the most contact with the
casing or open borehole, it experiences the most abrasive wear due
to the entrainment of sand and rock particles. It is therefore
advantageous to use hardbanding and multi-layer low friction
coatings together to provide for wear protection and low friction.
It is further advantageous to apply hardbanding in a patterned
design wherein grooves between hardbanding material allow for the
flow of particles past the hardbanded region without becoming
entrained and abrading the interface. It is even further
advantageous to reduce the contact area between hardbanding and
casing or open borehole to mitigate sticking or balling by rock
cuttings. The multi-layer low friction coatings could be applied in
any arrangement, but preferably it would be applied to the entire
area of the pattern since material passing through the passageways
of the pattern would have reduced chance of sticking to the
pipe.
[0106] An aspect of the present disclosure relates to an
advantageous coated drill stem assembly for subterraneous rotary
drilling operations comprising: a body assembly with an exposed
outer surface including a drill string coupled to a bottom hole
assembly, a coiled tubing coupled to a bottom hole assembly, or a
casing string coupled to a bottom hole assembly, hardbanding on at
least a portion of the exposed outer surface of the body assembly,
where the hardbanding surface may or may not have a patterned
design, a multi-layer low friction coating on at least a portion of
the hardbanding, and one or more buttering layers interposed
between the hardbanding and the multi-layer low friction
coating.
[0107] A further aspect of the present disclosure relates to an
advantageous method for reducing friction in a coated drill stem
assembly during subterraneous to rotary drilling operations
comprising: providing a drill stem assembly comprising a body
assembly with an exposed outer surface including a drill string
coupled to a bottom hole assembly, a coiled tubing coupled to a
bottom hole assembly, or a casing string coupled to a bottom hole
assembly, hardbanding on at least a portion of the exposed outer
surface of the body assembly, where the hardbanding surface may or
may not have a patterned design, a multi-layer low friction coating
on at least a portion of the hardbanding, and one or more buttering
layers interposed between the hardbanding and the multi-layer low
friction coating, and utilizing the coated drill stem assembly in
subterraneous rotary drilling operations.
[0108] A still further aspect of the present disclosure relates to
the interposition of one or more buttering layer(s) between the
outer surface of the body assembly or hardbanding, and the
multi-layer low friction coating. The buttering layer may be
created or deposited as a result of one or more techniques
including electrochemical or electroless plating methods, Plasma
Vapor Deposition (PVD) or Plasma Assisted Chemical Vapor Deposition
(PACVD) methods, carburizing, nitriding or boriding methods, or
ultra-fine superpolishing methods. The buttering layer may be
graded, and may serve several functional purposes, including but
not limited to: decreased surface roughness, enhanced adhesion with
other layer(s), enhanced mechanical integrity and performance.
[0109] A still further aspect of the present disclosure relates to
the advantageous method of forming one or more buttering layer(s)
interposed between the outer surface of the body assembly or
hardbanding, and the multi-layer low friction coating. The
buttering layer may be created or deposited as a result of one or
more techniques including electrochemical or electroless plating
methods, Plasma Vapor Deposition (PVD) or Plasma Assisted Chemical
Vapor Deposition (PACVD) methods, carburizing, nitriding or
boriding methods, or ultra-fine superpolishing methods. The
buttering layer may be graded, and may serve several functional
purposes, including but not limited to: decreased surface
roughness, enhanced adhesion with other layer(s), enhanced
mechanical integrity and performance.
[0110] In another embodiment, the buttering layer may be used in
conjunction with hardbanding, where the hardbanding is on at least
a portion of the exposed outer or inner surface to provide enhanced
wear resistance and durability to the coated drill stem assembly,
where the hardbanding surface may have a patterned design that
reduces entrainment of abrasive particles that contribute to wear.
In addition, the multi-layer low friction coating may be deposited
on top of the buttering layer.
Further Details Regarding Individual Layers and Interfaces
[0111] Further details regarding the functional layers for use in
the multi-layer low friction coatings disclosed herein are as
follows:
Fullerene Based Composites:
[0112] Fullerene based composite coating layers which include
fullerene-like nanoparticles may also be used as the functional
layer(s). Fullerene-like nanoparticles have advantageous
tribological properties in comparison to typical metals while
alleviating the shortcomings of conventional layered materials
(e.g., graphite, MoS.sub.2). Nearly spherical fullerenes may also
behave as nanoscale ball bearings. The main favorable benefit of
the hollow fullerene-like nanoparticles may be attributed to the
following three effects, (a) rolling friction, (b) the fullerene
nanoparticles function as spacers, which eliminate metal to metal
contact between the asperities of the two mating metal surfaces,
and (c) three body material transfer. Sliding/rolling of the
fullerene-like nanoparticles in the interface between rubbing
surfaces may be the main friction mechanism at low loads, when the
shape of nanoparticle is preserved. The beneficial effect of
fullerene-like nanoparticles increases with the load. Exfoliation
of external sheets of fullerene-like nanoparticles was found to
occur at high contact loads (.about.1 GPa). The transfer of
delaminated fullerene-like nanoparticles appears to be the dominant
friction mechanism at severe contact conditions. The mechanical and
tribological properties of fullerene-like nanoparticles can be
exploited by the incorporation of these particles in binder phases
of coating layers. In addition, composite coatings incorporating
fullerene-like nanoparticles in a metal binder phase (e.g., Ni--P
electroless plating) can provide a film with self-lubricating and
excellent anti-sticking characteristics suitable for the functional
layer of the multi-layer low friction coatings disclosed
herein.
Super-Hard Materials (Diamond, Diamond-Like-Carbon):
[0113] Super-hard materials such as diamond, and
diamond-like-carbon (DLC) may be used as the functional layer of
the multi-layer low friction coatings disclosed herein. Diamond is
the hardest material known to man and under certain conditions may
yield low coefficient of friction when deposited by chemical vapor
deposition (abbreviated herein as CVD).
[0114] In one advantageous embodiment, diamond-like-carbon (DLC)
may be used as the functional layer of the multi-layer low friction
coatings disclosed herein. DLC refers to amorphous carbon material
that display some of the unique properties similar to that of
natural diamond. Suitable diamond-like-carbon (DLC) layers or
coatings may be chosen from ta-C, ta-C:H, DLCH, PLCH, GLCH, Si-DLC,
titanium containing diamond-like-carbon (Ti-DLC), chromium
containing diamond-like-carbon (Cr-DLC), Me-DLC, F-DLC, S-DLC,
other DLC layer types, and combinations thereof. DLC coatings
include significant amounts of sp.sup.3 hybridized carbon atoms.
These sp.sup.3 bonds may occur not only with crystals--in other
words, in solids with long-range order--but also in amorphous
solids where the atoms are in a random arrangement. In this case
there will be bonding only between a few individual atoms, that is
short-range order, and not in a long-range order extending over a
large number of atoms. The bond types have a considerable influence
on the material properties of amorphous carbon films. If the
sp.sup.2 type is predominant the DLC film may be softer, whereas if
the sp.sup.3 type is predominant, the DLC film may be harder.
[0115] DLC coatings may be fabricated as amorphous, flexible, and
yet primarily sp.sup.3 bonded "diamond". The hardest is such a
mixture known as tetrahedral amorphous carbon, or ta-C. Such ta-C
includes a high volume fraction (.about.80%) of sp.sup.3 bonded
carbon atoms. Optional fillers for the DLC coatings, include, but
are not limited to, hydrogen, graphitic sp.sup.2 carbon, and
metals, and may be used in other forms to achieve a desired
combination of properties depending on the particular application.
The various forms of DLC coatings may be applied to a variety of
substrates that are compatible with a vacuum environment and that
are also electrically conductive. DLC coating quality is also
dependent on the fractional content of alloying and/or doping
elements such as hydrogen. Some DLC coating methods require
hydrogen or methane as a precursor gas, and hence a considerable
percentage of hydrogen may remain in the finished DLC material. In
order to further improve their tribological and mechanical
properties, DLC films are often modified by incorporating other
alloying and/or doping elements. For instance, the addition of
fluorine (F), and silicon (Si) to the DLC films lowers the surface
energy and wettability. The reduction of surface energy in
fluorinated DLC (F-DLC) is attributed to the presence of -CF2 and
-CF3 groups in the film. However, higher F contents may lead to a
lower hardness. The addition of Si may reduce surface energy by
decreasing the dispersive component of surface energy. Si addition
may also increase the hardness of the DLC films by promoting
sp.sup.3 hybridization in DLC films. Addition of metallic elements
(e.g., W, Ta, Cr, Ti, Mo) to the film can reduce the compressive
residual stresses resulting in better mechanical integrity of the
film upon compressive loading.
[0116] The diamond-like phase or sp.sup.3 bonded carbon of DLC is a
thermodynamically metastable phase while graphite with sp.sup.2
bonding is a thermodynamically stable phase. Thus the formation of
DLC coating films requires non-equilibrium processing to obtain
metastable sp.sup.3 bonded carbon. Equilibrium processing methods
such as evaporation of graphitic carbon, where the average energy
of the evaporated species is low (close to kT where k is Boltzman's
constant and T is temperature in absolute temperature scale), lead
to the formation of 100% sp.sup.2 bonded carbons. The methods
disclosed herein for producing DLC coatings require that the carbon
in the sp.sup.3 bond length be significantly less than the length
of the sp.sup.2 bond. Hence, the application of pressure, impact,
catalysis, or some combination of these at the atomic scale may
force sp.sup.2 bonded carbon atoms closer together into sp.sup.3
bonding. This may be done vigorously enough such that the atoms
cannot simply spring back apart into separations characteristic of
sp.sup.2 bonds. Typical techniques either combine such a
compression with a push of the new cluster of sp.sup.3 bonded
carbon deeper into the coating so that there is no room for
expansion back to separations needed for sp.sup.2 bonding; or the
new cluster is buried by the arrival of new carbon destined for the
next cycle of impacts.
[0117] The DLC coatings disclosed herein may be deposited by
physical vapor deposition, chemical vapor deposition, or plasma
assisted chemical vapor deposition coating techniques. The physical
vapor deposition coating methods include RF-DC plasma reactive
magnetron sputtering, ion beam assisted deposition, cathodic arc
deposition and pulsed laser deposition (PLD). The chemical vapor
deposition coating methods include ion beam assisted CVD
deposition, plasma enhanced deposition using a glow discharge from
hydrocarbon gas, using a radio frequency (r.f.) glow discharge from
a hydrocarbon gas, plasma immersed ion processing and microwave
discharge. Plasma enhanced chemical vapor deposition (PECVD) is one
advantageous method for depositing DLC coatings on large areas at
high deposition rates. Plasma-based CVD coating process is a
non-line-of-sight technique, i.e. the plasma conformally covers the
part to be coated and the entire exposed surface of the part is
coated with uniform thickness. The surface finish of the part may
be retained after the DLC coating application. One advantage of
PECVD is that the temperature of the substrate part does not
generally increase above about 150.degree. C. during the coating
operation. The fluorine-containing DLC (F-DLC) and
silicon-containing DLC (Si-DLC) films can be synthesized using
plasma deposition technique using a process gas of acetylene
(C.sub.2H.sub.2) mixed with fluorine-containing and
silicon-containing precursor gases respectively (e.g.,
tetra-fluoro-ethane and hexa-methyl-disiloxane).
[0118] The DLC coatings disclosed herein may exhibit coefficients
of friction within the ranges earlier described. The low COF may be
based on the formation of a thin graphite film in the actual
contact areas. As sp.sup.3 bonding is a thermodynamically unstable
phase of carbon at elevated temperatures of 600 to 1500.degree. C.,
depending on the environmental conditions, it may transform to
graphite which may function as a solid lubricant. These high
temperatures may occur as very short flash (referred to as the
incipient temperature) temperatures in the asperity collisions or
contacts. An alternative theory for the low COF of DLC coatings is
the presence of hydrocarbon-based slippery film. The tetrahedral
structure of a sp.sup.3 bonded carbon may result in a situation at
the surface where there may be one vacant electron coming out from
the surface, that has no carbon atom to attach to, which is
referred to as a "dangling bond" orbital. If one hydrogen atom with
its own electron is put on such carbon atom, it may bond with the
dangling bond orbital to form a two-electron covalent bond. When
two such smooth surfaces with an outer layer of single hydrogen
atoms slide over each other, shear will take place between the
hydrogen atoms. There is no chemical bonding between the surfaces,
only very weak van der Waals forces, and the surfaces exhibit the
properties of a heavy hydrocarbon wax. Carbon atoms at the surface
may make three strong bonds leaving one electron in the dangling
bond orbital pointing out from the surface. Hydrogen atoms attach
to such surface which becomes hydrophobic and exhibits low
friction.
[0119] The DLC coatings for the functional layer of the multi-layer
low friction coatings disclosed herein also prevent wear due to
their tribological properties. In particular, the DLC coatings
disclosed herein demonstrate enhanced resistance to wear and
abrasion making them suitable for use in applications that
experience extreme contact pressure and severe abrasive
environments.
Buttering Layers:
[0120] In yet another embodiment of the multi-layer low friction
coatings herein, the device may further include one or more
buttering layers interposed between the outer surface of the body
assembly or hardbanding layer and the layers comprising the
multi-layer low friction coating on at least a portion of the
exposed outer surface.
[0121] In one embodiment of the nickel based alloy used as a
buttering layer, the layer may be formed by electroplating.
Electro-plated nickel may be deposited as a buttering layer with
tailored hardness ranging from 150-1100, or 200 to 1000, or 250 to
900, or 300 to 700 Hv. Nickel is a silver-white metal, and
therefore the appearance of the nickel based alloy buttering layer
may range from a dull gray to an almost white, bright finish. In
one form of the nickel alloy buttering layers disclosed herein,
sulfamate nickel may be deposited from a nickel sulfamate bath
using electroplating. In another form of the nickel alloy buttering
layers disclosed herein, watts nickel may be deposited from a
nickel sulfate bath. Watts nickel normally yields a brighter finish
than does sulfamate nickel since even the dull watts bath contains
a grain refiner to improve the deposit. Watts nickel may also be
deposited as a semi-bright finish. Semi-bright watts nickel
achieves a brighter deposit because the bath contains organic
and/or metallic brighteners. The brighteners in a watts bath level
the deposit, yielding a smoother surface than the underlying part.
The semi-bright watts deposit can be easily polished to an ultra
smooth surface with high luster. A bright nickel bath contains a
higher concentration of organic brighteners that have a leveling
effect on the deposit. Sulfur-based brighteners are normally used
to achieve leveling in the early deposits, and a sulfur-free
organic, such as formaldehyde, is used to achieve a fully bright
deposit as the plating layer thickens. In another form, the nickel
alloy used for the buttering layer may be formed from black nickel,
which is often applied over an under plating of electrolytic or
electroless nickel. Among the advantageous properties afforded by a
nickel based buttering layer, include, but are not limited to,
corrosion prevention, magnetic properties, smooth surface finish,
appearance, lubricity, hardness, reflectivity, and emissivity.
[0122] In another embodiment, the nickel based alloy used as a
buttering layer may be formed as an electroless nickel plating. In
this form, the electroless nickel plating is an autocatalytic
process and does not use externally applied electrical current to
produce the deposit. The electroless process deposits a uniform
coating of metal, regardless of the shape of the part or its
surface irregularities; therefore, it overcomes one of the major
drawbacks of electroplating, the variation in plating thickness
that results from the variation in current density caused by the
geometry of the plated part and its relationship to the plating
anode. An electroless plating solution produces a deposit wherever
it contacts a properly prepared surface, without the need for
conforming anodes and complicated fixtures. Since the chemical bath
maintains a uniform deposition rate, the plater can precisely
control deposit thickness simply by controlling immersion time.
Low-phosphorus electroless nickel used as a buttering layer may
yield the brightest and hardest deposits. Hardness ranges from
60-70 R.sub.C (or 697 Hv.about.1076 Hv). In another form,
medium-phosphorus or mid-phos may be used as a buttering layer,
which has a hardness of approximately 40-42 R.sub.C (or 392
Hv.about.412 Hv). Hardness may be improved by heat-treating into
the 60-62 R.sub.C (or 697 Hv.about.746 Hv) range. Porosity is
lower, and conversely corrosion resistance is higher than
low-phosphorous electroless nickel. High-phosphorous electroless
nickel is dense and dull in comparison to the mid and
low-phosphorus deposits. High-phosphorus exhibits the best
corrosion resistance of the electroless nickel family; however, the
deposit is not as hard as the lower phosphorus content form.
High-phosphorus electroless nickel is a virtually non-magnetic
coating. For the nickel alloy buttering layers disclosed herein,
nickel boron may be used as an underplate for metals that require
firing for adhesion. The NiP amorphous matrix may also include a
dispersed second phase. Non-limiting exemplary dispersed second
phases include: i) electroless NiP matrix incorporated fine nano
size second phase particles of diamond, ii) electroless NiP matrix
with hexagonal boron nitride particles dispersed within the matrix,
and iii) electroless NiP matrix with submicron PTFE particles (e.g.
20-25% by volume Teflon) uniformly dispersed throughout
coating.
[0123] In yet another embodiment, the buttering layer may be formed
of an electroplated chrome layer to produce a smooth and reflective
surface finish. Hard chromium or functional chromium plating
buttering layers provide high hardness that is in the range of 700
to 1,000, or 750 to 950, or 800 to 900 H.sub.V, have a bright and
smooth surface finish, and are resistant to corrosion with
thicknesses ranging from 20 .mu.m to 250, or 50 to 200, or 100 to
150 .mu.m. Chromium plating buttering layers may be easily applied
at low cost. In another form of this embodiment, a decorative
chromium plating may be used as a buttering layer to provide a
durable coating with smooth surface finish. The decorative chrome
buttering layer may be deposited in a thickness range of 0.1 .mu.m
to 0.5 .mu.m, or 0.15 .mu.m to 0.45 .mu.m, or 0.2 .mu.m to 0.4
.mu.m, or 0.25 .mu.m to 0.35 .mu.m. The decorative chrome buttering
layer may also be applied over a bright nickel plating.
[0124] In still yet another embodiment, the buttering layer may be
formed on the body assembly or hardbanding from a super-polishing
process, which removes machining/grinding grooves and provides for
a surface finish below 0.25 .mu.m average surface roughness
(Ra).
[0125] In still yet another embodiment, the buttering layer may be
formed on the body assembly or hardbanding by one or more of the
following non-limiting exemplary processes: PVD, PACVD, CVD, ion
implantation, carburizing, nitriding, boronizing, sulfiding,
siliciding, oxidizing, an electrochemical process, an electroless
plating process, a thermal spray process, a kinetic spray process,
a laser-based process, a friction-stir process, a shot peening
process, a laser shock peening process, a welding process, a
brazing process, an ultra-fine superpolishing process, a
tribochemical polishing process, an electrochemical polishing
process, and combinations thereof.
Interfaces:
[0126] The interfaces between various layers in the coating may
have a substantial impact on the performance and durability of the
coating. In particular, non-graded interfaces may create sources of
weaknesses including one or more of the following: stress
concentrations, voids, residual stresses, spallation, delamination,
fatigue cracking, poor adhesion, chemical incompatibility,
mechanical incompatibility. One non-limiting exemplary way to
improve the performance of the coating is to use graded
interfaces.
[0127] Graded interfaces allow for a gradual change in the material
and physical properties between layers, which reduces the
concentration of sources of weakness. One non-limiting exemplary
way to create a graded interface during a manufacturing process is
to gradually stop the processing of a first layer while
simultaneously gradually commencing the processing of a second
layer. The thickness of the graded interface can be optimized by
varying the rate of change of processing conditions. The thickness
of the graded interface may range from 0.01 to 10 .mu.m or 0.05 to
9 .mu.m, or 0.1 to 8 .mu.m or 0.5 to 5 .mu.m. Alternatively the
thickness of the graded interface may range from 5% to 95% of the
thickness of to the thinnest adjacent layer.
Test Methods
High-Sand CETR Block-on-Ring Test:
[0128] This test was designed to simulate a high load (i.e., high
contact pressure) and high abrasion environment. Ring specimens
were rotated at various speeds and loads against a 6.36 mm wide
steel block (hardness .about.300-350 Hv) at ambient temperature.
The steel counterface was translated at a reciprocating speed of 1
mm/s perpendicular to the axis of the rotation of the ring in order
to maintain uniformity in wear across the ring. The lubricating
medium used for this study consisted of an oil-based slurry
(Oil:Water=1:9) where water was used as a continuous phase. A
poly-alpha-olefin oil of viscosity 8 cSt at 100.degree. C. was
used. This made the emulsion viscosity approximately 0.009 PaS at
the test temperature which is comparable to the viscosity of a
typical oil based mud under similar conditions. The slurry
contained 50 wt. % sand (silica) of 150 .mu.m mean diameter. The
slurry was introduced into a containing chamber into which the ring
was partially immersed for the duration of the test. The sand was
fully homogenized in the lubricating medium prior to the test by
introducing the slurry (in a sealed container) in a magnetic
stirrer for 30 minutes. The rotation of the ring prevented the
sedimentation of particles in the reservoir during the test. The
friction coefficient values during each wear test were recorded
automatically by a computer. The block wear (scar depth) was
measured by scanning the wear track in a stylus profilometer while
the coating wear was estimated based on the visual inspection. The
block wear was used as the measure of counterface friendliness for
any given coating. It should be noted that all coatings yielded low
coefficient of friction (typically <0.1), as long the DLC
remained intact during the CETR-BOR test.
Modified ASTM G105 Abrasion Test:
[0129] This is a wet sand/rubber wheel abrasion test designed to
simulate a lower load and very severe abrasion environment. The
standard ASTM G105 test is run using rubber wheels of four
different Shore hardness. However, in order to avoid complexity,
the ASTM G105 test was modified for this study where the specimen
was tested in contact against a rotating rubber wheel of given
shore is hardness (A 58-62). Tests were run in a Falex wear tester
keeping the rubber wheel partially submerged in a mixture of sand
and water. The wheel was rotated at 200 rpm for 30 minutes against
a vertically placed flat test specimen (1''.times.3'') under 30 lbf
load. The diameter and width of the wheel was 9'' and 0.5''
respectively. The slurry contained 60% SiO.sub.2 sand (round) and
40% water. At the completion of the tests, specimens have been
investigated for coating durability and performance determined by
(a) residual coating on plate (visual examination--percent of wear
zone covered by top layer coating after test), (b) mass loss, (c)
profilometry to measure wear scar depth and (d) microscopy.
Reported wear scar depth is the maximum depth of the wear groove
measured by scanning the stylus along the length of the wear track
created by the rubber wheel through the middle of the wear zone
width.
EXAMPLES
Illustrative Example 1
[0130] The two steps as outlined below were used to improve coating
durability in severe abrasive/loading conditions.
Step 1: Thick/Superthick Underlayer Structures:
[0131] Deposition of the DLC and adhesion promoting layers can be
done through a process such as PACVD, where a source and/or target
is used to deposit the DLC layer and the underlayer (e.g.,
Cr.sub.xN, Ti.sub.xN etc.). In some cases, the DLC layer (usually
1-5 .mu.m) is deposited directly onto a substrate without any
underlayer. In other cases, an underlayer (typically 2-5 .mu.m) is
deposited onto the substrate before DLC deposition (on the
underlayer). The underlayer provides some mechanical integrity and
toughness through load shielding while also providing some adhesion
enhancement with the substrate. Generally, lower underlayer
thicknesses help to improve overall coating performance in less
severe conditions (e.g., low abrasion/load), the coating durability
remains very poor under conditions where high abrasion/loads are
encountered, mainly due to the plastic deformation of the substrate
and abrasive wear of the DLC itself.
[0132] Finite Element Analysis (FEA) indicates that the
transmission of loads through sand grains can initiate significant
deformation of the underlying substrate at indentation depths of
<1 .mu.m, which is possible under high-load operating
conditions. In fact, with larger sand grains (.about.25-50 .mu.m),
the level of substrate plastic deformation (locally) can be quite
high (>10%), leading to delamination and cracking of coating
near the underlayer/substrate interface. Furthermore, the plastic
deformation in the substrate can change the stress state in the
underlayer/DLC interface, further reducing the load-bearing
capacity of the DLC coating. The delamination/cracking of the
coating is accelerated by the high compressive residual stress
within the DLC coating which creates a complex local stress state
conducive to coating removal (debonding).
[0133] By systematically increasing the underlayer thickness (to
.gtoreq.10-15 .mu.m), a more effective load-shielding layer can be
created, thus significantly minimizing plastic deformation of the
substrate. Experiments and abrasion test results (discussed below)
illustrate the beneficial effect on coating durability as a
function of increasing underlayer (CrN) thickness. The deposition
of such thick underlayers is a technically challenging process, and
may require a good control of stoichiometry (e.g., alternating CrN
and Cr.sub.2N layers to manage residual stress) and longer
deposition times (typical deposition rates for CrN: 1 .mu.m per
40-50 minutes).
Step 2: Thick/Superthick, Superhard and/or Composite DLC
Structures:
[0134] While Step 1 (above) helps minimize plastic deformation of
the substrate, it does not directly address the issue of DLC
performance (i.e., durability) in severe abrasive conditions.
[0135] In wear involving an abrading medium (i.e., sand), the ratio
of the hardness of the abrading medium and coating (i.e. surface
being abraded) determines overall abrasion rate (according to the
open literature). Under this premise, increasing coating hardness
can help reduce abrasive wear. However, increased hardness of DLC
coatings comes at the expense of increasing residual stress, which
causes issues with coating cracking/delamination/spalling. Thus,
this aspect leads to a focus on "optimal" hardness as opposed to
"extreme" hardness. Our experiments indicate that hardness values
of 2500-5500 (Hv) can be targeted, in combination with effective
underlayer thicknesses, while not compromising coating durability
(through cracking/spalling) severely for the thicker coating
architectures.
[0136] Given a coating hardness, which in turn determines abrasion
rate (assuming a gradual abrasion mechanism dominates as opposed to
coating cracking/spalling), the overall durability of the coating
depends on the coating thickness. By systematically increasing the
thickness of the DLC layer (to values >15 .mu.m), it has been
shown that the coating durability can be improved in severe
abrasive/loading conditions (discussed below). The deposition of
such DLC layers is a technically challenging process requiring good
control over interlayer adhesion (where applicable) and chemistry,
management of residual stress, and process control to avoid chamber
contamination, while requiring long deposition times (typical DLC
deposition rates: 1 .mu.m for every 80-100 minutes). In some cases,
the beneficial effects of using harder functional layers such as
ta-C, in combination with thicker underlayers and adhesion
promoting layers, can also be realized.
[0137] The intrinsic abrasion resistance of the DLC depends upon
the coating chemistry. A multilayer of a-C:H alternating with CrC
can be created to enhance overall intrinsic toughness and abrasion
resistance of the multilayer. The a-C:H phase is essential to
provide the low friction properties, while the CrC phase provides
toughness and higher resistance to abrasion. Results indicating
superior abrasion resistance of such a multilayer are also
presented (below). Alternatively, a combination of a harder
functional layer (e.g., ta-C) with a targeted thickness of
underlayer (such as CrN), may also yield superior abrasion
resistance along with improved toughness and durability of the
coating.
Results Summarizing the Combined Benefits of Step 1 and Step 2:
[0138] Table 1 below shows a summary of nine different coating
architectures tested to evaluate the effect of the approaches/steps
outlined above (in some cases, values of adhesion promoting layer
thicknesses are not explicitly reported). Two types of
tests/experiments were designed and conducted to evaluate coating
durability: CETR block on ring (high sand) test, and modified ASTM
G105 test. These tests, and associated measurements from each are
described above.
TABLE-US-00001 TABLE 1 Summary of coating architectures and test
results CETR Block Residual coating ASTM G105 ASTM G105 ASTM G105 %
wear scar after CETR weight max. scar DLC intact # Coating
Description depth (.mu.m) test (%) loss (g) depth (.mu.m)* after
test A Thin coating 2 .mu.m CrN + ~450 <15 0.0516 27 0 1 .mu.m
DLC B Moderate DLC 2 .mu.m CrN + ~50 ~50 0.0406 25 0 thickness 5
.mu.m DLC 5 .mu.m CrN + ~60 >70 0.0083 ~6-8 30 5 .mu.m DLC C
Thick underlayer 10 .mu.m CrN + ~150 >80 0.0058 ~8 0 5 .mu.m DLC
D Thick underlayer + 15 .mu.m CrN + ~200 >90 0.0041 ~10 40 thick
DLC 10 .mu.m DLC E Thick underlayer + 15 .mu.m CrN + ~100 >95
0.0028 ~9 60 Thick 10 .mu.m multilayer DLC) Multilayer (CrC/DLC) F
Thick underlayer + 15 .mu.m CrN + ~640 >90 0.0008 0 100 Thick
ta-C 6 .mu.m ta-C G Thick underlayer + 15 .mu.m CrN + ~320 >95
0.0065 ~2 60 Thick 15 .mu.m CrC + multilayer + 15 .mu.m DLC Thick
DLC H taC/graded DLC Thin Cr + ~170 >90 0.0237 ~29 0 2 .mu.m
ta-C + 4 .mu.m DLC I Thick underlayer + 7 .mu.m CrN + ~171 >95
0.0016 ~4 >80 taC/graded 2 .mu.m taC + DLC 5 .mu.m graded
DLC
[0139] FIG. 1 illustrates microscopy investigations on some
selective coatings (A-F from Table 1). Indications of a good
coating performance and durability are: low block wear (i.e., good
casing friendliness), high % of residual coating after CETR-BOR or
ASTM test (i.e. good coating durability in high-load abrasive
test), low weight loss and scar depth in ASTM G105 test (i.e.
minimal coating removal and/or substrate removal during test).
[0140] The beneficial effects of (a) thick underlayers, (b) thick
and multilayer composite DLC structures, and (c) superhard top
layer coatings are apparent from the results presented in this
study. The cumulative effects of these approaches may yield a
coating architecture (e.g., similar to architecture E, F) with the
significantly improved overall durability among the evaluated
specimens, in test conditions designed to simulate high
loading/abrasion environments. When using weight loss in ASTM tests
as a measure, it can be seen that Architecture E (thick
underlayer+thick multilayer DLC) is approximately 20 times better
than Architecture A (thin DLC) In addition, architecture F (thick
underlayer+thick ta-C) is approximately 70-100 times better than
Architecture A (thin DLC) in terms of overall durability as
measured by resistance to wear/abrasion in the G105 test. The
significant improvement in abrasion resistance using thick
underlayer and thick coating was also apparent for the superhard
ta-C coating (Architecture I vs. Architecture H).
[0141] Applicants have attempted to disclose all embodiments and
applications of the disclosed subject matter that could be
reasonably foreseen. However, there may be unforeseeable,
insubstantial modifications that remain as equivalents. While the
present disclosure has been described in conjunction with specific,
exemplary embodiments thereof, it is evident that many alterations,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description without departing
from the spirit or scope of the present disclosure. Accordingly,
the present disclosure is intended to embrace all such alterations,
modifications, and variations of the above detailed
description.
[0142] All patents, test procedures, and other documents cited
herein, including priority documents, are fully incorporated by
reference to the extent such disclosure is not inconsistent with
this disclosure and for all jurisdictions in which such
incorporation is permitted.
[0143] When numerical lower limits and numerical upper limits are
listed herein, ranges from any lower limit to any upper limit are
contemplated.
* * * * *
References