U.S. patent application number 14/742561 was filed with the patent office on 2016-12-22 for ti-si-c-n piston ring coatings.
The applicant listed for this patent is Southwest Research Institute. Invention is credited to Daniel Christopher BITSIS, JR., Peter Mark LEE, Jianliang LIN, Ronghua WEI.
Application Number | 20160369391 14/742561 |
Document ID | / |
Family ID | 57538525 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160369391 |
Kind Code |
A1 |
LIN; Jianliang ; et
al. |
December 22, 2016 |
TI-SI-C-N PISTON RING COATINGS
Abstract
A Ti--Si--C--N coating for a piston ring and a method forming
such coating, wherein the deposited coating exhibits a thickness in
the range of 10.0 micrometers to 20.0 micrometers and exhibits a
coefficient of friction of less than 0.15 and a wear rate of less
than 10-10.sup.-6 mm.sup.3/N/m. The coefficient of friction being
measured on a Plint TE77 and the wear rate being measured against
an alumina ball of 0.25 inches in diameter at a load of 1 N at 100
rpm in a dry environment. The deposited Ti--Si--C--N coating
includes nanocrystalline phases in an amorphous matrix.
Inventors: |
LIN; Jianliang; (Helotes,
TX) ; WEI; Ronghua; (San Antonio, TX) ; LEE;
Peter Mark; (Fair Oaks Ranch, TX) ; BITSIS, JR.;
Daniel Christopher; (San Antonio, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Southwest Research Institute |
San Antonio |
TX |
US |
|
|
Family ID: |
57538525 |
Appl. No.: |
14/742561 |
Filed: |
June 17, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16J 9/28 20130101; C23C
14/35 20130101; C23C 14/0057 20130101; C23C 14/345 20130101; C23C
14/0664 20130101; F16J 9/26 20130101; C23C 14/355 20130101 |
International
Class: |
C23C 14/06 20060101
C23C014/06; F16J 9/28 20060101 F16J009/28; F16J 9/26 20060101
F16J009/26; C23C 14/35 20060101 C23C014/35; C23C 14/34 20060101
C23C014/34 |
Claims
1. A method of coating piston rings, comprising: placing a piston
ring into a process chamber; reducing gas pressure in said process
chamber; supplying an inert gas to said process chamber and
generating a plasma of said inert gas; supplying nitrogen to said
process chamber at a flow rate of 40 sccm to 60 sccm; supplying
hexamethyldisilazane to said process chamber at a rate of 3 grams
per hour to 9 grams per hour; sputtering titanium from a magnetron
target in said process chamber; and depositing a Ti--Si--C--N
coating on said piston ring, wherein said coating has a thickness
in the range of 10.0 micrometers to 40.0 micrometers and exhibits a
coefficient of friction of less than 0.15, a wear rate of less than
10.times.10.sup.-6 mm.sup.3/N/m, and a nanohardness in the range of
10.0 GPa to 30.0 GPa, wherein said coefficient of friction is
measured using a Plint TE77 testing apparatus using 10 W-30 oil
maintained at 35.degree. C. as a lubricant, under a force of 30 N,
and a sliding frequency of 5 to 20 Hz, and said wear rate is
measured against an alumina ball of 0.25 inches in diameter at a
load of 1 N at 100 rpm in a dry environment, wherein said
Ti--Si--C--N coating includes nanocrystalline phases having a grain
size in the range of 3 nm to 10 nm in an amorphous matrix, wherein
said nanocrystalline phases include TiC.sub.xN.sub.y, wherein x is
in the range of 0.00 to 1.00 and y is in the range of 1.00 to
0.00.
2. The method of claim 1, wherein said nitrogen is supplied to said
process chamber as nitrogen gas, ammonia, or combinations
thereof.
3. The method of claim 1, further comprising supplying carbon to
said process chamber, wherein said carbon is supplied as acetylene,
methane, or combinations thereof.
4. The method of claim 1, further comprising negatively biasing an
electron source in the range of 50 V to 120 V to form said plasma
and said process chamber is biased in the range of 50 V to 150 V
relative to said electron source.
5. The method of claim 1, wherein said piston ring is negatively
biased in the range of 20 V to 200 V and said magnetron is
negatively biased in the range of 0.05 to 10 kW.
6. The method of claim 1, wherein said deposited coating comprises
titanium present in the range of 35 to 49 atomic percent, silicon
present in the range of 1 to 5 atomic percent, carbon present in
the range of 17 to 41 atomic percent, and nitrogen present in the
range of 19 to 35 atomic percent.
7. The method of claim 1, wherein said deposited coating comprises
titanium present in the range of 43.5 to 46.7 atomic percent,
silicon present in the range of 1.58 to 3.04 atomic percent, carbon
present in the range of 17.6 to 22.5 atomic percent, and nitrogen
present in the range of 30.9 to 34.2 atomic percent.
8. The method of claim 7, wherein the coefficient of friction is in
the range of 0.21 to 0.26, and the wear rate is in the range of
3.02 to 7.35.times.10.sup.-6 mm.sup.3/N/m.
9. The method of claim 1, further comprising supplying acetylene to
said process chamber at a flow rate in the range of 10 sccm to 30
sccm and said deposited coating comprises titanium present in the
range of 38 to 48.4 atomic percent, silicon present in the range of
1.84 to 2.34 atomic percent, carbon present in the range of 21.5 to
38.1 atomic percent, and nitrogen present in the range of 21.59 to
28.09 atomic percent.
10. The method of claim 9, wherein the coefficient of friction is
in the range of 0.21 to 0.33, the wear rate may be in the range of
4.59.times.10.sup.-6 mm.sup.3/N/m to 5.02.times.10.sup.-6
mm.sup.3/N/m, and the nanohardness may be in the range of 14.5 GPa
to16.7 GPa.
11. The method of claim 1, further comprising supplying acetylene
to said process chamber at a flow rate in the range of 15 sccm to
25 sccm and said deposited coating comprises titanium present in
the range of 35.6 to 43.3 atomic percent, silicon present in the
range of 2.33 to 4.12 atomic percent, carbon present in the range
of 29.0 to 40.8 atomic percent, and nitrogen present in the range
of 19.64 to 25.34 atomic percent.
12. The method of claim 11, wherein the coefficient of friction is
in the range of 0.16 to 0.21, the wear rate is in the range of
3.84.times.10.sup.-6 mm.sup.3/N/m to 5.78.times.10.sup.-6
mm.sup.3/N/m, the nanohardness is in the range of 13.8 GPa to 14.5
GPa.
13. The method of claim 1, further comprising supplying acetylene
to said process chamber wherein said deposited coating comprises
titanium present in the range of 41 to 43.3 atomic percent, silicon
present in the range of 2.3 to 3.8 atomic percent, carbon present
in the range of 29 to 33 atomic percent, and nitrogen present in
the range of 22 to 25 atomic percent.
14. The method of claim 13, wherein the coefficient of friction may
be in the range of 0.21 to 0.22 and the wear rate is in the range
of 4.69.times.10.sup.-6 mm.sup.3/N/m to 5.78.times.10.sup.-6
mm.sup.3/N/m.
15. The method of claim 1, wherein said amorphous matrix includes
one of the following compositions: diamond like carbon, Si--N, and
Si--N--C.
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
Description
FIELD OF INVENTION
[0001] The present disclosure is directed to piston ring coatings
and to the preparation of piston ring coatings of Ti--Si--C--N
using plasma enhanced magnetron sputtering techniques.
BACKGROUND
[0002] Automobile manufacturers and component makers have been
engineering automotive components to achieve the gradually
increasing Corporate Average Fuel Economy (CAFE) standards, which
target an average fleet fuel consumption of 34.1 MPG by 2016 and
56.2 MPG by 2025. One design initiative to achieve CAFE standards
is the reduction in the coefficient of friction of moving parts. In
addition to achieving CAFE standards, a reduction in the
coefficient of friction may also reduce wear and improve
reliability of moving components.
[0003] One such moving part is the piston ring. One or more piston
rings are commonly provided in grooved tracks around the outer
perimeter of an engine piston. Where multiple rings are present,
the rings may be designed to perform different or overlapping
functions. For example, piston rings may be designed to seal the
combustion chamber to trap combustion gasses, improving engine
efficiency. Piston rings may also be designed to aid in heat
transfer and manage engine oil in the cylinder.
[0004] Piston rings are often formed from a base material of cast
iron or rolled carbon steel and may be coated with relatively hard,
wear resistant coatings, such as nitride coatings, exhibiting
hardness 2 to 4 times that of the base materials. Chromium nitride
coatings may exhibit relatively low internal stress allowing for
relatively thick coating layers. Chromium nitride coating
deposition rates are considered somewhat favorable for production
at deposition rates of approximately 2 microns per hour. Titanium
nitride coatings have also been examined. However, titanium nitride
coatings may exhibit relatively high internal stress compared to
chromium nitride coatings.
[0005] The coefficient of friction for chromium nitride and
titanium nitride coatings may be in the range of 0.5 to 0.7 in dry
sliding as measured by typical pin-on-disc testing. Reducing the
coefficient of friction values between a piston and cylinder liner
wall may reduce overall engine friction and improve fuel
efficiency. However, maintaining relatively high deposition rates,
relatively high hardness and relatively high wear resistance is
also desirable. Accordingly, a need for providing a relatively
hard, wear resistant, and cost effective piston ring coating
exhibiting a relatively lower coefficient of friction still
remains.
SUMMARY
[0006] An aspect of the present disclosure relates to a method of
coating piston rings. The piston ring may be placed into a process
chamber and gas pressure in the process chamber may be reduced.
Inert gas may then be supplied to the process chamber and plasma
may be generated from the inert gas. The coatings may then be
formed by supplying nitrogen gas into the process chamber at a flow
rate of 40 sccm to 60 sccm, supplying hexamethyldisilazane at a
rate of 3 grams per hour to 9 grams per hour, supplying acetylene
at a rate of 10 standard cubic centimeters per minute (sccm) to 50
sccm, and sputtering titanium from a magnetron target. A
Ti--Si--C--N coating is deposited on the piston ring having a
thickness in the range of 10.0 micrometers to 40.0 micrometers and
exhibits a coefficient of friction of less than 0.15, a wear rate
of less than 10.times.10.sup.-6 mm.sup.3/N/m, and a nanohardness in
the range of 10.0 GPa to 30.0 GPa. The coefficient of friction is
measured using the Plint TE77 testing apparatus using a 10 W-30 oil
maintained at 35.degree. C. as a lubricant, a normal force of 30 N,
and a sliding frequency of 5 to 20 Hz. The wear rate is measured
against an alumina ball of 0.25 inches in diameter at a load of 1 N
at 100 rpm in a dry environment, i.e., without lubricant. In
addition, the Ti--Si--C--N coating includes nanocrystalline phases
in an amorphous matrix, wherein the nanocrystalline phases include
TiC.sub.xN.sub.y, wherein x is in the range of 0.0 to 1.0 and y is
in the range of 1.0 to 0.0.
[0007] A further aspect of the present disclosure relates to a
coated piston ring. The coated piston ring may include a split ring
formed of an iron based alloy. A Ti--Si--C--N coating deposited on
the surface of the piston ring may have a thickness in the range of
10.0 micrometers to 40.0 micrometers that exhibits a coefficient of
friction of less than 0.4, a wear rate of less than
10.times.10.sup.-6 mm.sup.3/N/m, and a nanohardness in the range of
10.0 GPa to 30.0 GPa. The coefficient of friction is measured using
the Plint TE77 testing apparatus using a 10 W-30 oil maintained at
35.degree. C. as a lubricant, a normal force of 30 N, and a sliding
frequency of 5 to 20 Hz. The wear rate is measured against an
alumina ball of 0.25 inches in diameter at a load of 1 N at 100 rpm
in a dry environment. The Ti--Si--C--N coating includes
nanocrystalline phases in an amorphous matrix, wherein the
nanocrystalline phases include TiC.sub.xN.sub.y, wherein x is in
the range of 0.0 to 1.0 and y is in the range of 1.0 to 0.0.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The above-mentioned and other features of this disclosure,
and the manner of attaining them, will become more apparent and
better understood by reference to the following description of
embodiments described herein taken in conjunction with the
accompanying drawings, wherein:
[0009] FIG. 1 illustrates a perspective exploded view of a piston
and piston rings;
[0010] FIG. 2 illustrates a schematic of a process chamber;
[0011] FIG. 3 illustrates a schematic of a pin-on-disk
tribometer;
[0012] FIG. 4a illustrates a schematic of the Plint TE77 test;
[0013] FIG. 4b illustrates the testing conditions for Plint TE77
testing;
[0014] FIG. 5 illustrates an image of a single cylinder Ricardo
Hydra gasoline engine;
[0015] FIG. 6 illustrates a single cylinder Caterpillar oil test
engine;
[0016] FIG. 7 is a graph of the measured nanohardness and Young's
modulus of samples 1 through 7;
[0017] FIG. 8 is a graph of the coefficient of friction and wear
rate obtained of samples 1 through 7 measured using the pin-on-disk
tribometer;
[0018] FIG. 9 is a graph of the effect of acetylene flow rate on
the coefficient of friction and wear rate of sample 8 through
14;
[0019] FIG. 10 is a graph illustrating the effect of sample
preparation conditions on the coefficient of friction as measured
by the Plint TE77 tribometer;
[0020] FIG. 11 is a graph illustrating the effect of sample
preparation conditions on the coefficient of friction as measured
by the Plint TE77 tribometer;
[0021] FIG. 12 is a graph illustrating the effect of sample
preparation conditions on the coefficient of friction as measured
by the Plint TE77 tribometer;
[0022] FIG. 13a is a graph illustrating the effect of sample
preparation conditions on the composition of the coatings;
[0023] FIG. 13b includes XRD patterns illustrating the effect of
sample preparation conditions on the composition of the
coatings;
[0024] FIG. 14a is a graph illustrating the effect of sample
preparation conditions on the composition of the coatings;
[0025] FIG. 14b includes XRD patterns illustrating the effect of
sample preparation conditions on the composition of the
coatings;
[0026] FIG. 15a includes SEM images of nanoindentations on the
coatings of, from top to bottom, samples 3, 4, and 5, the scale set
forth in the lower left hand corner is 200 .mu.m;
[0027] FIG. 15b includes SEM images of the surface of the coatings
of, from top to bottom, samples 3, 4, and 5, the scale set forth in
the lower left hand corner is 5 .mu.m;
[0028] FIG. 15c includes SEM images of cross-sections of the
coatings of, from top to bottom, samples 3, 4, and 5, the scale set
forth in the lower left hand corner is 5 .mu.m;
[0029] FIG. 16a includes SEM images of nanoindentations on the
coatings of, from top to bottom, samples 8, 11, 12 and 13, the
scale set forth in the lower left hand corner is 200 .mu.m;
[0030] FIG. 16b includes SEM images of the surface of the coatings
of, from top to bottom, samples 8, 11, 12 and 13, the scale set
forth in the lower left hand corner is 5 .mu.m;
[0031] FIG. 16c includes SEM images of cross-sections of the
coatings of, from top to bottom, samples 8, 11, 12 and 13, the
scale set forth in the lower left hand corner is 5 .mu.m;
[0032] FIG. 17a includes SEM images of nanoindentations on the
coatings of, from top to bottom, samples 15, 16, and 17, the scale
set forth in the lower left hand corner is 200 .mu.m;
[0033] FIG. 17b includes SEM images of the surface of the coatings
of, from top to bottom, samples 15, 16, and 17, the scale set forth
in the lower left hand corner is 5 .mu.m;
[0034] FIG. 17c includes SEM images of cross-sections of the
coatings of, from top to bottom, samples 15, 16, and 17, the scale
set forth in the lower left hand corner is 5 .mu.m;
[0035] FIG. 18a is a TEM image of a cross-section of the
Ti--Si--C--N coating;
[0036] FIG. 18b is an SAED pattern of the Ti--Si--C--N
nanocomposite coating;
[0037] FIG. 19a is a photograph of coated rings, coated according
to the conditions of samples 11 and 16;
[0038] FIG. 19b illustrates a 3D graph of the topography of a
section of the top ring generated with a 3D microscope after
running the engine for 24 hours;
[0039] FIG. 19c is a profile of the coating taken in the
x-direction generated with a 3D a microscope after running the
engine for 24 hours;
[0040] FIG. 19d is a profile taken in the y-direction generated
with a 3D microscope after running the engine for 24 hours;
[0041] FIG. 20 is a graph of the absolute magnitude of the friction
in one engine cycle for coated and uncoated piston rings;
[0042] FIG. 21a is a schematic of the 12 points around a combustion
cylinder liner used to take the 12 point step measurements;
[0043] FIG. 21b is a graph of the liner wear versus the clock
position around the combustion cylinder at which the wear was
measured;
[0044] FIG. 21c illustrates the measurements of average liner wear
of all 12 liner wear steps;
[0045] FIG. 22a illustrates the amount of iron measured by
inductively coupled plasma analysis in engine oil for both coated
and baseline piston rings; and
[0046] FIG. 22b illustrates the amount of titanium measured by
inductively coupled plasma analysis in engine oil for both coated
and baseline piston rings.
DETAILED DESCRIPTION
[0047] Piston rings are commonly used to provide a seal between a
piston and the cylinder liner so that the engine combustion chamber
can achieve a desired pressure. As illustrated in FIG. 1, one or
more piston rings 102, 104, 106, 108, 110 may be provided around
the outer perimeter of an engine piston 100 and are often held in
grooved tracks 112, 114, 116 formed in the surface 120 of the
piston 100. Where multiple rings are present, the rings may be
designed to perform different or overlapping functions. For
example, compression rings 102, 104 may be designed to seal the
combustion chamber to trap combustion gasses and oil control rings
may be designed to manage engine oil in the cylinder. Spacer rings
108 may be provided between two rings 106, 110 to keep the rings
spaced apart and is common in oil control ring arrangements. Due to
the sliding action of the piston and piston ring against the
cylinder liner wall, reducing the coefficient of friction between
the piston ring and wall may help improve the efficiency of the
engine. In combination with exhibiting a relatively low coefficient
of friction, it is also desirable for piston rings to exhibit high
hardness and low wear rates so as to maintain their integrity over
the life cycle of the engine.
[0048] The present disclosure is directed to Ti--Si--C--N coated
piston rings and methods of forming such rings. Referring again to
FIG. 1, the piston rings 102, 104, 106, 108, 110 may be split rings
with a split 124 that allows the rings to open and expand for
placement over the piston. While the split is illustrated as being
a vertical split, the split may assume a number of configurations.
The piston rings may be formed from an iron based alloy, wherein
the alloy includes at least 50 atomic percent of iron. Examples
include cast iron, steel, or stainless steel. In addition, the
rings may exhibit a variety of cross-sectional configurations
including barrel face, keystone, torsional, reverse torsional,
wiper, or keystone torsional configurations.
[0049] The piston rings are coated with Ti--Si--C--N coatings. The
Ti--Si--C--N coatings may comprise, consist essentially of, or
consist of titanium present in the range of 35 to 49 atomic
percent, including all values and ranges therein, silicon present
in the range of 1 to 5 atomic percent, including all values and
ranges therein, carbon present in the range of 17 to 41 atomic
percent, including all values and ranges therein, and nitrogen
present in the range of 19 to 35 atomic percent, including all
values and ranges therein. In embodiments, the coatings include a
composition of 43.5 to 46.7 atomic percent titanium, 1.58 to 3.04
atomic percent silicon, 30.9 to 34.2 atomic percent nitrogen, and
17.6 to 22.5 atomic percent carbon.
[0050] In preferred embodiments, the coatings preferably include a
composition of 38 to 48.4 atomic percent titanium, 1.84 to 2.34
atomic percent silicon, 21.59 to 28.09 atomic percent nitrogen, and
21.5 to 38.1 atomic percent carbon. In further preferred
embodiments, the coatings preferably include a composition of 35.6
to 43.3 atomic percent titanium, 2.33 to 4.12 atomic percent
silicon, 19.64 to 25.34 atomic percent nitrogen, and 29.0 to 40.8
atomic percent carbon. In more preferred embodiments, the coatings
preferably include titanium present in the range of 41 to 43.3
atomic percent, silicon present in the range of 2.3 to 3.8 atomic
percent, carbon present in the range of 29 to 33 atomic percent,
and nitrogen present in the range of 22 to 25 atomic percent.
[0051] As noted, the coatings may comprise or consist essentially
of the elements of titanium, silicon, carbon and nitrogen at or
within the ranges noted above or consist of the elements of
titanium, silicon, carbon and nitrogen at or within the ranges
noted above, with the understanding that some amount of impurities
may be present depending on the level of impurities present in the
feed stocks or introduced by the deposition process. For example,
the feed stocks or gasses may be supplied containing impurities.
Such impurities may be present in the range of 0.001 to 1.0 atomic
percent, including all values and ranges therein.
[0052] The deposited Ti--Si--C--N coatings may exhibit
nanocrystalline phases in an amorphous matrix. The nanocrystalline
phases may include TiC.sub.xN.sub.y phases. In such phases x is in
the range of 0.00 to 1.00, including all values and ranges therein,
such as 0.00, 0.01 to 1.00, 0.01 to 0.10, 0.10 to 1.00, etc. and y
is in the range of 1.00 to 0.00, including all values and ranges
therein, such as 0.00, 1.00 to 0.01, 1.00 to 0.10, 0.10 to 0.01,
etc. In embodiments, TiC.sub.xN.sub.y phases may include TiN,
TiC.sub.0.3N.sub.0.7, TiC.sub.0.7N.sub.0.3, Ti.sub.4N.sub.3, and
combinations thereof. In particular embodiments, y is equal to 1-x,
wherein TiC.sub.xN.sub.(1-x), and phases include TiN,
TiC.sub.0.3N.sub.0.7, TiC.sub.0.7N.sub.0.3, etc. The
nanocrystalline phases may exhibit a grain size in the range of 3
nm to 10 nm, including all values and ranges therein, such as 4.5
nm to 7 nm.
[0053] The amorphous matrix includes a composition selected from
diamond like carbon (DLC), Si--N and Si--C--N, with the
understanding that impurities may be present from 0.001 to 1 atomic
percent in the amorphous phase, including all values and ranges
therein. Again, impurities may be introduced in the feedstocks or
in the deposition process. In particular embodiments, the amorphous
matrix may include diamond like carbon including varying ratios of
sp.sup.2 bonded and sp.sup.3 bonded phases, including all sp.sup.2
phases or all sp.sup.3 phases.
[0054] The coatings may be formed at a thickness of 10 to 40
micrometers, including all values and ranges therein, such as 10 to
20 micrometers. The coatings provide a coefficient of friction of
less than 0.15, including all values and ranges therein, such as in
the range of 0.05 to 0.15, 0.05 to 0.10, etc., as measured on a
Plint TE77 testing apparatus using a 10 W-30 oil maintained at
35.degree. C., a normal force of 30 N, and a sliding frequency of 5
to 20 Hz. The coatings may also provide a coefficient of friction
in the range of less than 0.4, including all values and ranges
therein such as in the range of 0.16 to 0.4, 0.16 to 0.33, 0.21 to
0.33, 0.16 to 0.21, 0.21 to 0.22, as determined via a pin-on-disc
tribometer using an alumina ball of 0.25 inches in diameter at a
load of 1 N at 100 rpm in a dry environment.
[0055] The coatings may further provide a nanohardness hardness of
10.0 GPa to 30.0 GPa, including all values and ranges therein, such
as in the range of 10 GPa to 20 GPa, 14.5 GPa to 16.7 GPa, 13.8 GPa
to 14.5 GPa, 14.5 GPa, etc., as measured by a nanoindenter
(NanoIndenter XP.TM., MTS Systems Corporation) equipped with a
diamond Berkovich indenter by taking 12 effective measurements. In
addition, the coatings may provide a wear rate of less than
10.times.10.sup.-6 mm.sup.3/N/m, including all values and ranges
therein, such as from 3.02.times.10.sup.-6 mm.sup.3/N/m to
7.35.times.10.sup.-6 mm.sup.3/N/m, 4.59.times.10.sup.-6 to
5.025.times.10.sup.-6 mm.sup.3/N/m, 3.84.times.10.sup.-6 to
5.78.times.10.sup.-6 mm.sup.3/N/m, 4.69.times.10.sup.-6
mm.sup.3/N/m to 5.78.times.10.sup.-6 mm.sup.3/N/m, wherein the wear
rate is determined via a pin-on-disc tribometer using an alumina
ball of 0.25 inches in diameter at a load of 1 N at 100 rpm in a
dry environment. The ability of the coatings, and coated piston
rings, to exhibit all three of these characteristics at thicknesses
of 40 micrometers or less, and particularly at a thickness of 20
microns or less, is contemplated to provide not only improved
engine performance in terms of efficiency but also an increase in
engine life span over coatings that exhibit a relatively higher
coefficient of friction.
[0056] The Ti--Si--C--N coatings may be deposited using physical
vapor deposition. In particular, plasma enhanced magnetron
sputtering of titanium in the presence of nitrogen,
hexamethyldisilizane, and, optionally, a carbon containing gas.
Generally, plasma enhanced magnetron sputtering may utilize a gas
plasma in the chamber to assist in the coating process, forming
denser coatings. In the present process, to introduce silicon,
carbon and nitrogen into the coatings, nitrogen gas and
hexamethyldisilizane may be supplied to the process chamber during
the sputtering process. Acetylene may also be supplied to the
process chamber during the sputtering process to increase the
carbon content of the coatings. In addition to, or alternatively,
nitrogen may be introduced into the process by providing ammonia to
the chamber and carbon may be introduced into the process by
providing methane to the chamber.
[0057] With reference to FIG. 2, a process chamber 200 may be
provided including a substrate holder 204 on which substrates
(i.e., piston rings) 202a, 202b (referred to herein as substrate
202) may be mounted. While the process chamber may be grounded, a
power supply 201 may be provided to positively bias the process
chamber wall 203 relative to other components associated with the
process chamber, such as an electron source, work table, substrate
or magnetron. Another power supply 205 may be provided to
negatively bias the substrate holder 204, the substrate 202 or
both. The power supplies 201, 205 may individually be selected as
an AC, DC or RF power supply.
[0058] A vacuum system 206 may also be provided to reduce the
pressure within the process chamber. The vacuum system 206 may
include an outlet in the process chamber 200 that is in fluid
communication through a flow path with one or more vacuum pumps. In
addition, one or more valves may be provided in the vacuum system
206 to regulate the flow of gasses in the chamber.
[0059] The process chamber may further include one or more gas
supply ports 208. One or more gasses may be provided through each
gas supply port 208. Gasses provided through the gas supply ports
may include argon or other inert gasses such as krypton or xenon.
Further process gasses that may form a portion of the coating, such
as nitrogen or acetylene, may also be provided through the gas
supply port.
[0060] An electron source 210 may also be provided in the process
chamber 200. The electron source 210 may include, for example, a
hollow cathode, an RF antenna, a microwave generator, a thermionic
filament or a combination thereof. As illustrated, the electron
source 210 is a single thermionic filament, which may be formed
from tungsten or tantalum. The filament may discharge electrons
into the system when heated to the thermionic emission temperature
of the material forming the filament. An energy source 211, i.e.,
power supply, may be used to apply a bias to the electron source
210 and may include an AC, DC or RF power supply.
[0061] A precursor system may be provided to supply
hexamethyldisilizane to the process chamber 200. The precursor
system may include a vessel 216 for storage of the
hexamethyldisilizane as a liquid and one or more tubes or pipes to
provide a flow path 218 between the vessel 216 to the process
chamber 200. A mass flow controller 220 may be provided in
communication with the flow path to regulate the amount of
hexamethyldisilizane entering the process chamber. The vessel 216,
flow path 218, and mass flow controller 220 may be heated at a
temperature in the range of about 30.degree. C. to 50.degree. C.
using, for example, heater bands, hot air, hot water or hot oil. A
liquid flow controller may be used instead of heating the vessel
216. Heating the precursor system, or at least a portion thereof,
may volatilize the hexamethyldisilizane so that it may be
introduced to the process chamber 200 in vapor form. The precursor
system may also include a purging system 222 for clearing gasses
out of the flow path 218 to prevent contamination of the
hexamethyldisilizane entering the process chamber 200. The purging
system may reduce the pressure in the flow path 218 to reduce, or
substantially reduce, the presence of gasses in the flow path
218.
[0062] The metal (titanium) may be provided by a magnetron. As
illustrated, there are two magnetrons 224a, 224b (referred to
herein as 224) provided in the process chamber. The magnetrons 224
may each include a target 226a, 226b (herein after 226), which
provides the metal source for the coatings. The magnetrons may also
each include magnets 225a, 225b (hereinafter 225), which provide a
magnetic field in the range of 500 Gauss to 1,000 Gauss, including
all values and ranges therein. The magnets may create magnetic
fields along the length and surface of each target. A power supply
227a, 227b (herein after 227) to bias the magnetron 224 with a
negative bias may also be provided.
[0063] To coat the piston rings, the piston rings may be provided
as a substrate 202 into the process chamber 200. Once the substrate
202 is positioned on a work table 204 in the process chamber 200,
the gas in the process chamber 200 may be evacuated and the gas
pressure reduced to a pressure in the range of 10.sup.-5 torr to
10.sup.-6 ton, including all values and ranges therein, via the
vacuum system 206. In embodiments, argon or another inert gas such
as krypton, xenon, etc., may be supplied to the chamber through a
gas supply port 208 at a rate of 1 to 200 standard cubic
centimeters per minute (sccm), including all values and ranges
therein, such as a rate of 5 to 50 sccm. The pressure in the
chamber may be maintained at a range of 1 to 10 millitorrs,
including all values and ranges therein, using the vacuum system
206. The inert gas may be continuously fed into the chamber through
the duration of the sputtering process as well as through the
deposition process.
[0064] The substrate 202 may optionally be sputter cleaned prior to
coating by applying a bias to the work table 204, the substrate
202, an electron source 210, chamber wall 203 or a combination
thereof. The negative bias applied to the work table or substrate
may be in the range of 20 V to 200 Volts including all values and
ranges therein, such as in the range of 40 V to 100 V. The bias
applied to the work table or substrate may result in the drawing of
ions from the argon gas or global plasma to the substrate and
sputter cleaning the substrate. Ions may be drawn to the substrate
or work table at 50 to 300 eV, including all values and increments
therein.
[0065] The electron source may be negatively biased in the range of
50 V to 120 V, including all values and ranges therein, such as 75
V to 120 Volts etc. Applying a bias to the electron source 210 may
result in electrons being ejected into the process chamber 200,
causing collisions with the inert gas and separating the gas into
ions and electrons, thus forming plasma. In addition, the chamber
wall 203 may be positively biased in the range of 50 to 150 volts,
including all values and ranges therein, such as 90 to 100 volts,
relative to the filament. In applying a bias to the chamber wall
203, electrons may be drawn from the electron source 210 to the
wall surfaces. The electrons may collide with neutral inert gas
ions (e.g., argon ions) forming global plasma GP throughout the
process chamber 200. The sputter cleaning process may occur for 10
to 200 minutes, including all values and ranges therein such as in
the range of 60 to 90 minutes, removing surface oxides and/or
contaminants.
[0066] During deposition the flow rate of inert gas into the
chamber through the gas port 208 may be maintained in the range of
1 to 200 sccm, including all values and ranges therein, such as at
a rate of 5 to 50 sccm. Nitrogen gas may also be supplied to the
process chamber at a flow rate in the range of 40 to 60 sccm,
including all values and ranges therein, such as 45 to 50 sccm,
through the gas port 208. In embodiments, a separate gas port may
be provided for supplying nitrogen. Acetylene may also be
introduced into the process chamber 200. The acetylene may be
introduced through gas port 208 or a separate gas port may be
provided for the acetylene. If introduced, the acetylene may be
provided at a flow rate in the range of 10 to 30 sccm, including
all values and ranges therein, such as from 15 to 25 sccm, etc.
Hexamethyldisilizane may also be introduced into the process
chamber 200 through the precursor system at a rate in the range of
3 grams per hour to 9 grams per hour of hexamethyldisilizane may be
introduced into the process chamber 200, including all values and
ranges therein, such as from 3 to 6 grams per hour.
[0067] The biases applied to the substrate, worktable, chamber
wall, and electron source may also be maintained during deposition.
The negative bias applied to the work table or substrate may be in
the range of 20 V to 200 V including all values and ranges therein,
such as in the range of 40 V to 100 V. The electron source may be
negatively biased in the range of 50 V to 120 V, including all
values and ranges therein, such as 75 V to 120 Volts etc. The
resulting current to the work table or substrate may be in the
range of 0.5 A to 20 A, including all values and ranges therein. In
addition, the chamber wall 203 may be positively biased in the
range of 50 to 150 volts, including all values and ranges therein,
such as 90 to 100 volts, relative to the filament. The bias to the
chamber wall may be developed due to the relative charge of the
electron source and the chamber wall and the energy source 201 may
not be necessary to develop the bias.
[0068] The magnetron power supply 227 may negatively bias the
magnetron 224 at a range of 0.05 kilowatts to 10 kilowatts,
including all values and ranges therein, such as from 4 kilowatts
to 10 kilowatts. The negative bias applied to the magnetron 224 may
draw ions out of gasses proximate to the magnetron 224 forming
magnetron plasma P1, P2. Electrons may become trapped within the
magnetic fields generated by the magnets in the magnetrons
increasing collisions with the gasses near the magnetrons and
furthering ionization of the gasses. Due to the negative bias, ions
from the magnetron P1, P2 and global plasmas GP may be accelerated
toward the targets 226 with sufficient energy to remove or sputter
atoms from the targets 226.
[0069] While atoms are sputtered from the magnetron targets, ions
from the global plasma may bombard the surface of the substrate,
including the sputtered atoms of titanium, and produce a protective
coating including the atoms from the hexamethyldisilizane,
nitrogen, and acetylene (if present), on the surfaces of the
negatively biased substrate. The discharge conditions, i.e., the
condition of the global plasma, may be effective to induce the
reactive gas to react with the metal atoms. This then forms the
Ti--Si--C--N coatings on the piston ring.
[0070] During deposition, the discharge current may be in the range
of 1 to 10 A, including all values and ranges therein, such as in
the range of 4.5 to 5.5 A, 5 A, etc. The discharge current may be
understood as related to the plasma density or ion current. The
bias voltage is in the range of 30 to 100 V including all values
and ranges therein, such as 30 to 50 V, 40 V, etc. The bias voltage
may be understood as a measure of ion energy. The bias current may
be in the range of 0.50 to 1.00 A, including all values and ranges
therein, such as 0.51 to 0.92 A. The bias current may be understood
as a measure of ion flux.
[0071] Deposition may proceed from 3 to 10 hours, including all
values and ranges therein, such as 3 to 5, 3.5 and 4. As noted
above, the coatings may be formed at a thickness in the range of 10
to 40 micrometers, including all values and ranges therein. The
coatings may be relatively uniform in thickness, wherein the
thickness of the coatings may vary +/-20% or less of the average
thickness across the coating surface.
[0072] In embodiments, prior to depositing the Ti--Si--C--N
coatings a bond coat is deposited on the substrate. The bond coat
may include titanium, titanium nitride, or a combination thereof.
For example, the bond coat may include one or more alternating
layers of titanium and titanium nitride. In other examples, the
bond coat may include one or more layers of titanium nitride phases
dispersed in a titanium matrix.
[0073] As noted, the deposited Ti--Si--C--N coatings preferably
include titanium present in the range of 35 to 49 atomic percent,
including all values and ranges therein, silicon present in the
range of 1 to 5 atomic percent, including all values and ranges
therein, carbon present in the range of 17 to 41 atomic percent,
including all values and ranges therein, and nitrogen present in
the range of 19 to 35 atomic percent, including all values and
ranges therein. These formulations of the coatings exhibit a
remarkable combination of properties, including a coefficient of
friction of less than 0.15, a wear rate of less than
10.times.10.sup.-6 mm.sup.3/N/m, and a nanohardness in the range of
13.0 GPa to 30.0 GPa. The coefficient of friction is measured using
the Plint TE77 testing apparatus using a 10 W-30 oil maintained at
35.degree. C. as a lubricant, a normal force of 30 N, and a sliding
frequency of 5 to 20 Hz. The wear rate is measured against an
alumina ball of 0.25 inches in diameter at a load of 1 N at 100 rpm
in a dry environment.
[0074] In embodiments, particularly where acetylene is not present
in the process environment, the coatings preferably include a
composition of 43.5 to 46.7 atomic percent titanium, 1.58 to 3.04
atomic percent silicon, 30.9 to 34.2 atomic percent nitrogen, and
17.6 to 22.5 atomic percent carbon. In such embodiments, the
coefficient of friction may be in the range of 0.21 to 0.26 and the
wear rate may be in the range of 3.02.times.10.sup.-6 mm.sup.3/N/m
to 7.35.times.10.sup.-6 mm.sup.3/N/m, wherein the coefficient of
friction and wear rate as measured against an alumina ball of 0.25
inches in diameter at a load of 1 N at 100 rpm in a dry
environment.
[0075] In additional embodiments, where acetylene is introduced to
the process environment in the range of 10 sccm to 30 sccm, the
coatings preferably include a composition of 38 to 48.4 atomic
percent titanium, 1.84 to 2.34 atomic percent silicon, 21.59 to
28.09 atomic percent nitrogen, and 21.5 to 38.1 atomic percent
carbon. In such embodiments, the Plint TE77 coefficient of friction
is less than 0.15, including all values and ranges therein, such as
in the range of 0.05 to 0.10, as measured using 10 W-30 oil
maintained at 35.degree. C. as a lubricant, using a normal force of
30 N applied and a sliding frequency of 5 to 20 Hz. The pin-on-disc
coefficient of friction may be in the range of 0.21 to 0.33. The
wear rate may be in the range of 4.59.times.10.sup.-6 mm.sup.3/N/m
to 5.02.times.10.sup.-6 mm.sup.3/N/m. The pin-on-disc coefficient
of friction and wear rate being measured against an alumina ball of
0.25 inches in diameter at a load of 1 N at 100 rpm in a dry
environment. The nanohardness may be in the range of 14.5 GPa
to16.7 GPa.
[0076] In further embodiments, where acetylene is introduced to the
process environment in the range of 15 sccm to 25 sccm, the
coatings preferably include a composition of 35.6 to 43.3 atomic
percent titanium, 2.33 to 4.12 atomic percent silicon, 19.64 to
25.34 atomic percent nitrogen, and 29.0 to 40.8 atomic percent
carbon. In such embodiments, the Plint TE77 coefficient of friction
is less than 0.15, including all values and ranges therein, such as
in the range of 0.05 to 0.10, as measured using a 10 W-30 oil
maintained at 35.degree. C. as a lubricant, using a force of 30 N
and a sliding frequency of 5 to 20 Hz. The pin-on-disc coefficient
of friction may be in the range of 0.16 to 0.21 and the wear rate
may be in the range of 3.84.times.10.sup.-6 mm.sup.3/N/m to
5.78.times.10.sup.-6 mm.sup.3/N/m, wherein the coefficient of
friction and wear rate as measured against an alumina ball of 0.25
inches in diameter at a load of 1 N at 100 rpm in a dry
environment. The nanohardness may be in the range of 13.8 GPa to
14.5 GPa.
[0077] In yet further embodiments, where acetylene is introduced to
the process environment, such as at a flow rate of 15 to 25 sccm
and preferably 18 to 22 sccm and more preferably 20 sccm, the
coatings preferably include titanium present in the range of 41 to
43.3 atomic percent, silicon present in the range of 2.3 to 3.8
atomic percent, carbon present in the range of 29 to 33 atomic
percent, and nitrogen present in the range of 22 to 25 atomic
percent. In such embodiments, the Plint TE77 coefficient of
friction is less than 0.15, including all values and ranges
therein, such as in the range of 0.05 to 0.10, as measured using a
10 W-30 oil maintained at 35.degree. C. as a lubricant, using a
normal force of 30 N, and a sliding frequency of 5 to 20 Hz. The
pin-on-disc coefficient of friction may be in the range of 0.21 to
0.22 and the wear rate may be in the range of 4.69.times.10.sup.-6
mm.sup.3/N/m to 5.78.times.10.sup.-6 mm.sup.3/N/m, wherein the
coefficient of friction and wear rate as measured against an
alumina ball of 0.25 inches in diameter at a load of 1 N at 100 rpm
in a dry environment. The nanohardness may be in the range of 10 to
20 GPa, including all values and ranges therein, and preferably
14.5 GPa.
EXAMPLES
Samples
[0078] Stainless steel (SS) disc coupon samples (1 inch.times.1
inch.times.1/8 inch) and steel keystone 137 mm bore piston rings
were used in the examples herein. The coupons were used for the
coating microstructural analyses and pin-on-disc wear tests, while
the rings were tested in the Plint TE77 apparatus and single
cylinder engine test.
Coating Process
[0079] Ti--Si--C--N coatings were formed using the process
parameters described below in Table 1. Prior to coating deposition,
each sample substrate was cleaned by etching with inert ions using
a global plasma at a bias voltage of -120 V. The voltage and
current applied on the filaments during sputter cleaning were 20 V
and 40 A. After ion etching, a Ti/TiN bond layer was deposited to
enhance the adhesion strength of the coatings.
[0080] To form the coating two titanium targets were used in DC
magnetron sputtering at a 4 kW average power (MDX, 10 kW, Advanced
Energy, Inc.) positioned in the process chamber. Argon, nitrogen,
hexamethyldisilizane (HMDSN) and acetylene (C.sub.2H.sub.2) gasses
were supplied in the process chamber. Tungsten filaments were used
as an electron source. Argon flow rate was maintained at 190 sccm.
The chamber pressure was maintained at about 3 m Ton in all samples
and trials. Coatings having a thickness in the range of 12 to 15
microns were deposited for a deposition period of 3 hours.
TABLE-US-00001 TABLE 1 Processing Parameters 1.sup.st 2.sup.nd
Deposit Target Target Discharge Bias Bias Flow Rate Flow Rate Flow
Rate Time Power Power Current Voltage Current N.sub.2 HMDSN
C.sub.2H.sub.2 Sample (hr) (kW) (kW) (A) (V) (A) (sccm) (g/hr)
(sccm) 1 3 4 4 5 40 0.66 50 3 2 4 4 4 5 40 0.65 50 6 3 5 4 4 5 40
0.92 50 12 4 5 4 4 5 40 0.82 50 15 5 3.5 4 4 5 40 0.85 50 18 6 3 4
4 5 40 0.51 50 1.5 7 3 4 4 5 40 0.57 45 3 8 3 4 4 5 40 0.67 45 3 5
9 3 4 4 5 40 0.58 45 3 10 10 3 4 4 5 40 0.6 45 3 15 11 3 4 4 5 40
0.54 45 3 20 12 3 4 4 5 40 0.58 45 3 30 13 3 4 4 5 40 0.54 45 3 40
14 3 4 4 5 40 0.57 45 3 50 15 3 4 4 5 40 0.54 45 3 17.5 16 3 4 4 5
40 0.54 45 3 20 17 3 4 4 5 40 0.54 45 3 22.5 18 3 4 4 5 40 0.54 45
3 25
[0081] Three groups of coatings were deposited. In the first group,
samples 1-7, the flow rate of hexamethyldisilizane (HMDSN) was
varied, while no acetylene (C.sub.2H.sub.2) was introduced. In the
second group, samples 8-14, the flow rate of acetylene
(C.sub.2H.sub.2) was varied from 5 to 50 sccm while the flow rate
of hexamethyldisilizane was maintained at 3 g/hr. In the third
group, samples 15-18, the flow rate of acetylene (C.sub.2H.sub.2)
was varied from 17.5 to 25 sccm while the flow rate of
hexamethyldisilizane was maintained at 3 g/hr. The flow rate of
nitrogen (N.sub.2) was maintained at 50 sccm for samples 1 through
6 and 45 sccm for samples 7 through 18.
Experimental Procedures
[0082] Scanning electron microscopy (SEM) using a Philips XL 40
scanning electron microscope was used to study the coating
microstructure and morphology. Cross-sections were examined using
SEM to determine coating thickness. In addition, energy dispersive
spectroscopy (EDS) was used to perform elemental analysis. X-ray
diffractions were generated using a Siemens Kristalloflex 805
diffractometer using Cu radiation (45 kV and 30 mA) in
Bragg-Brentano mode.
[0083] Rockwell C indentation at 150 kg load was performed on the
coatings and then studied using SEM. Nanoindentation was also
performed on selected samples to study the coating nanohardness and
modulus of elasticity. The mean hardness and Young's modulus of the
Ti--Si--C--N coatings were measured using a nanoindenter
(NanoIndenter XP.TM., MTS Systems Corporation) with a diamond
Berkovich tip. The indentation depth was 300 nm, which was less
than 10% of the thickness of the coating to avoid the effect from
the substrate deformation. The hardness (H) and Young's modulus (E)
of the coating were calculated by the nanoindenter software
(TestWorks.TM. Ver.4.06A) based on the model of Oliver and Phan
from the load-displacement curves. Twelve measurements were made to
obtain the mean value and the standard deviation.
[0084] The adhesion of the coatings was measured by the Rockwell-C
indentation test (RC) using a standard Rockwell-C hardness tester.
A Rockwell C diamond stylus (cone apex angle 120.degree., tip
radius R=0.2 mm) was used to perform the tests with an applied load
of 150 kg on the stylus. After the tests, the morphology of the
indentations was examined using SEM to evaluate coating damage
around the indents. The damage of the coating was compared with a
HF adhesion strength quality as standardized in the VDI guidelines
3198, (1991).
[0085] Coating tribology was measured using a pin-on-disc
tribometer, a schematic of which is illustrated in FIG. 3. This
test was performed on the stainless steel disc coupons for
screening purposes. The counter pin used was an alumina ball of 6
mm in diameter and the applied load F was 1 N, and the rotating
speed was 100 rpm. The testing occurred in a non-lubricated
environment for 10,000 cycles.
[0086] A few of the coated rings were also tested using the Plint
TE77 testing apparatus, which was performed using diesel engine oil
as a lubricant. The oil was Shell ROTELLA, which is 10w-30 oil, and
had been drained from a prototype high efficiency heavy duty diesel
engine. This oil was used to provide stable friction measurements.
During testing, the oil temperature was maintained at 35.degree. C.
to provide the desired viscosity. FIG. 4a illustrates a schematic
of the test, wherein a sample is slide back and forth FS against a
sliding surface at a given frequency under a normal force F1, which
is applied normal to the sliding surface. FIG. 4b illustrates the
testing points, wherein the test was performed at frequencies of 5
Hz, 10 Hz, 15 Hz and 20 Hz and normal forces of 15 N, 30 N and 45
N.
[0087] After Plint TE77 testing the deposition parameters were
selected and a few rings were selected and tested in a single
cylinder Ricardo Hydra gasoline engine shown in FIG. 5. The test
was conducted using the following parameters: 0.5 L displacement,
86 mm piston, 86 mm stroke, and 10.5:1 compression ratio. The valve
train is characterized as a direct-acting lifter design, twin
overhead cam. Operating parameters of the engine include: 5 w20
fully formulated engine oil, 100.degree. C. engine coolant in and
out temperature, 250 kPa engine oil pressure, 65.degree. C. engine
oil gallery temperature, and 2000 rpm reciprocation. The engine was
run over a 24 hour period using a combination of motoring and
firing at steady and increasing speeds and loads.
[0088] Heavy duty diesel engine testing was then performed using
piston rings coated according to sample 11 for the top and second
compression rings (rings 102, 104 illustrated in FIG. 1). The
engine chosen was a single cylinder oil test engine as shown in
FIG. 6 using one cylinder from a Caterpillar 15 L engine. The
engine had a 137 mm bore, articulated steel piston with aluminum
skirt, and keystone top ring. The engine was operated at a peak
torque for 120 hours of continuous testing. Peak torque
(approximately 385 Nm) occurs at 1200 RPM. An oil drain from
another engine which contained 4.1% soot by mass was used to
accelerate the wear process. This test was operated with an engine
oil temperature of 125.degree. C. and oil gallery pressure of 350
kPa. During testing an inductively coupled plasma (ICP) analysis
was performed to check for wear materials every 12 hours, providing
an indicator of wear rate for different parameters such as the
coating and base metal.
Results and Discussion
Coating Properties and Elemental Composition
[0089] Tables 2 and 3 provide the experimental results indicating
the properties of the coatings and elemental coating
composition.
TABLE-US-00002 TABLE 2 Coating Properties Flow Rate Flow Rate
Deposition Wear Rate Nano- Modulus HMDSN C.sub.2H.sub.2 Thickness
Rate COF (pin- (.times.10.sup.-6 Hardness Elasticity Sample (g/hr)
(sccm) (.mu.m) (.mu.m/hr) on- disc) mm.sup.3/N/m) (GPa) (GPa) 1 3
0.25 5.1 29.4 350 2 6 0.26 3.02 25.8 305 3 12 20.1 4.02 0.4 14.6
21.5 311 4 15 19.6 3.92 0.7 17.8 20.6 302 5 18 13.1 3.74 0.9 25.6
8.3 149 6 1.5 17.5 5.83 0.93 36.1 27.6 334 7 3 11.1 3.70 0.21 7.35
8 3 5 20 6.67 0.55 4.33 21 295 9 3 10 16.5 5.50 0.33 4.59 16.7 255
10 3 15 13.5 4.50 0.24 5.02 11 3 20 14.4 4.80 0.22 4.69 14.5 183 12
3 30 16.5 5.50 0.21 4.71 13 3 40 10.1 3.37 0.19 2.96 13.4 133 14 3
50 19.5 6.50 0.16 12.3 15 3 17.5 16.6 5.53 0.18 4.59 16 3 20 16.1
5.37 0.21 5.78 17 3 22.5 16.2 5.40 0.19 4.59 18 3 25 17.4 5.80 0.19
3.84 13.8 138
TABLE-US-00003 TABLE 3 Elemental Compositions of the Coatings Flow
Rate Flow Rate HMDSN C.sub.2H.sub.2 C N Si Ti Sample (g/hr) (sccm)
(at %) (at %) (at %) (at %) 1 3 2 6 22.5 30.98 3.04 43.5 3 12 20
32.76 4.22 43 4 15 19.5 31.84 5.04 43.6 5 18 22 28.44 6.46 43.1 6
1.5 17.6 35.59 1.1 45.7 7 3 17.6 34.2 1.58 46.7 8 3 5 20.8 27.89
1.28 50 9 3 10 21.5 28.09 2.05 48.4 10 3 15 24 27.51 1.84 46.6 11 3
20 29 25.34 2.33 43.3 12 3 30 38.1 21.59 2.34 38 13 3 40 46.7 17.48
2.42 33.4 14 3 50 55.2 15.97 1.96 26.9 15 3 17.5 30.4 23.57 3.77
42.3 16 3 20 32.8 22.29 3.83 41.1 17 3 22.5 36.3 20.6 4.12 39 18 3
25 40.8 19.64 3.91 35.6
[0090] The nanohardness and modulus of samples 1 through 7 are
graphed in FIG. 7 relative to the flow rate of the
hexamethyldisilizane. As can be seen in the graph, both hardness
and modulus reach a maximum at 3 g/hr. As illustrated in FIG. 8 the
coefficient of friction and wear rate obtained using pin-on-disk
tribology is graphed relative to the flow rate of the
hexamethyldisilizane. As can be seen in the graph, the coefficient
of friction is lowest when the hexamethyldisilizane flow rate is at
3 grams per hour and remains below 0.4 at flow rates between 3
grams per hour and 12 grams per hour. Similarly, the wear rate is
lowest when the hexamethyldisilizane flow rate is in the range of 3
grams per hour and 6 grams per hour, remaining below
5.times.10.sup.-6 mm.sup.3/N/m. Based on the data, it appears that
at a flow rate of hexamethyldisilizane in the range of 3 grams per
hour and 9 grams per hour the coefficient of friction remains below
0.4 and the wear rate remains below 10.times.10.sup.-6
mm.sup.3/N/m.
[0091] As a flow rate of 3 grams per hour of hexamethyldisilizane
provided better properties overall, the hexamethyldisilizane flow
rate was maintained at 3 grams per hour while acetylene was
introduced into the system at varying flow rates in samples 8
through 14. FIG. 9 illustrates the effect of acetylene flow rate on
the coefficient of friction and the wear rate. As can be seen, in
FIG. 9, the coefficient of friction is below 0.4 at acetylene flow
rates of 10 sccm or greater. However, the wear rate increases at an
acetylene flow rate of 50 sccm to greater than 12.times.10.sup.-6
mm.sup.3/N/m. At 40 sccm and below, the wear rate remains below
about 5.times.10.sup.-6 mm.sup.3/N/m. In view of this data, it
appears that acetylene may be introduced at a flow rate in the
range of 10 sccm to 40 sccm, including all values and ranges
therein.
[0092] The coefficient of friction using the Plint TE77 test was
also measured for samples 8, 11, 12 and 13 and the results are
presented in FIG. 10. As seen in this figure, the coefficient of
friction was lower when the flow rate of acetylene was in the range
of 10 to 30 sccm. At these rates, the coefficients of friction were
similar, and lower at higher frequencies, than that of the baseline
of cast iron as seen in FIG. 10. Using flow rates of 5 sccm and 40
sccm resulted in a relatively higher coefficient of friction and a
relatively higher wear rate, respectively.
[0093] In view of the above, the acetylene flow rate was varied at
finer steps from 17.5 to 25 sccm. Note that sample 16 is a repeat
of sample 11. FIG. 11 illustrates the results of Plint TE77
testing. The performance of the coatings appears to be similar and,
at most frequencies, below that of the cast iron baseline material
seen in the graph. Specifically, it appears that at 10 Hz, the
coefficient of friction was below 0.09 for the samples tested,
whereas the coefficient of friction was above 0.09 for cast iron.
Similarly at 15 Hz, the coefficient of friction of the samples
appeared to be below 0.08, whereas the coefficient of friction of
the cast iron appears to be 0.08. At 20 Hz, the coefficient of
friction of the samples appears to be 0.065 or below, whereas the
coefficient of friction of the cast iron is above 0.065.
[0094] FIG. 12 illustrates the coefficient of friction as measured
by the Plint TE77 test for varying amounts of hexamethyldisilizane
in samples formed without acetylene present in the process chamber,
samples 3, 4 and 5. As seen in FIG. 12, the coefficient of friction
of these samples was relatively higher than that of the cast iron.
Note that these samples were tested at a normal force of 15 N
whereas all previous samples in FIGS. 10 and 11 were tested at 30
N.
[0095] With regard to the elemental compositions produced by the
coating methods, FIG. 13a illustrates the effect of HMDSN flow rate
on the coating composition for samples 2 through 6 and 7. The
amount of titanium was highest at 3 g/hr and the silicon content
increased relatively linearly with increasing hexamethyldisilizane
flow rate was kept the same. The highlighted area illustrates the
flow rate where the properties were relatively better overall. FIG.
13b presents the XRD patterns of the Ti--Si--C--N coatings
deposited with different HMDSN flow rates. All Ti--Si--C--N
coatings exhibited polycrystalline structure. The coating deposited
at a HMDSN flow rate of 1.5 g/hr exhibited a face center cubic
(FCC) phase structure with (111), (200), (220) diffraction peaks.
The (200) diffraction peaks showed the highest intensity. As the
HMDSN flow was increased to 3 and 6 g/hr, the intensity of the
(200) peak decreased with a peak broadening for all diffraction
peaks. In addition, the diffraction peaks for the Ti adhesion layer
and the steel substrate were also shown in the XRD patterns. Since
the thickness of the coatings is similar, the appearance of the Ti
diffraction peaks in the XRD patterns indicated an increase in the
amorphous phase in the Ti--Si--C--N coatings as the HMDSN flow rate
increased, as X-ray has a deep penetration depth in amorphous
phases.
[0096] FIGS. 14a and 14b illustrate the effect of acetylene flow
rate on the coating composition for samples 8 through 14. As seen
in FIG. 14a, the concentration of C increases with increasing
acetylene flow rate. Further, the concentrations of Ti and N
decrease and Si remains fairly consistent as the acetylene flow
rate increased. The highlighted area illustrates the flow rate
where the properties were relatively better overall. FIG. 14b
presents the XRD patterns. These coatings also exhibited an FCC
phase structure with (111), (200) and (220) diffraction peaks. As
the acetylene flow was increased, the intensity of the (200) peak
decreased accompanied with an increase in the (111) peak. The
diffraction peaks for the titanium adhesion layer and the steel
substrate increased significantly as the acetylene flow rate was
increase, which is related to an increase in the amorphous carbon
phase in the coatings.
SEM Imaging
[0097] FIGS. 15a, 15b and 15c illustrate SEM images of samples 3, 4
and 5 produced using hexamethyldisilizane without acetylene. In
each figure, sample 3 is at the top, sample 4 is in the middle, and
sample 5 is at the bottom of the images. FIG. 15a include images of
Rockwell C (RC) indentation on the coating surfaces, FIG. 15b
includes images of the coating surfaces without indentation, and
FIG. 15c includes images of cross-sectional views of the coatings.
Overall, the coatings include many droplets on the surface. In
addition, the coatings exhibit columnar structure. Further, at a
high hexamethyldisilizane flow rate, the coating becomes coarse.
Finally, delamination is not observed around the RC indents
indicating adhesion is relatively good.
[0098] FIGS. 16a, 16b, and 16c illustrate SEM images of samples 8,
11, 12 and 13, wherein sample 8 is at the top, sample 11 is at the
top middle, sample 12 is at the bottom middle, and sample 13 is at
the bottom of the images. FIG. 16a includes images of RC
indentation on the coating surfaces, FIG. 16b includes images of
the coating surfaces without indentation, and FIG. 16c includes
images of cross-sectional views of the coatings. It is noted that
as the amount of acetylene increases, the droplets and columnar
structure decreases. In addition, the surface morphological
features become smaller as acetylene flow rate increases. Finally,
the coatings become more brittle as acetylene flow rate increase.
Based on industry criteria, VDI 3198 (Verein Deutscher Ingenieure
Normen, VDI 3198, VDI-Verlag, Dusseldorf, 1991), the coating
adhesion for sample 8 was the best. Samples 11 and 12 are
acceptable. However, sample 13 is unacceptable.
[0099] FIGS. 17a, 17b and 17c illustrate SEM images of samples 15,
16 and 17, wherein sample 15 is at the top of the images, 16 is in
the middle and 17 in at the bottom. FIG. 17a includes images of RC
indentation on the coating surfaces. FIG. 17b includes images of
the coating surfaces. FIG. 17c includes images of cross-sectional
views of the coatings. The structure, morphology and indentation
appear to be similar. Few droplets on the coating surfaces are
observed. The columnar structure seen in samples 3, 4, and 5 is not
seen and delamination is not observed, indicating that adhesion is
relatively good.
[0100] In addition, it can be seen from FIGS. 18a and 18b that the
coatings have a nanocomposite structure. The coating imaged
contains nanocrystalline phases with nanocrystalline grain sizes
that fall in the range of 3 to 10 nm, which may be attributed to
the TiCN crystalline phases. The amorphous phase was found to be
mainly composed of Si--C--N. FIG. 18b includes a selected area
electron diffraction (SAED) pattern of the coating which confirms
the coating has a polycrystalline face center cubic (FCC) phase
which may be attributed to the TiCN.
Friction Test
[0101] A set of piston rings were produced including the top,
second and oil control ring, by coating rings using the depositions
parameters used in Samples 11 and 16 described above. This set of
rings was installed on the friction engine. The engine was run over
an 8 hour period using a combination of motoring and firing at
steadily increasing speeds (1500, 2000, 2500, 3000 and 2500 rpm)
and loads (40,60 and 75% engine load). The ring wear was measured
using optical profilometry and the wear depth was barely measurable
at less than 1 micron. FIG. 19a is a photograph of the coated rings
on the piston and FIG. 19b is a 3D microscope image of the top
ring. FIG. 19c is a profile taken in the x-direction using the 3D
microscope and FIG. 19d is a profile taken in the y-direction using
the 3D microscope after running in the engine for 24 hours.
[0102] The coefficient of friction contribution from the coated
rings in the single cylinder engine was obtained using the
difference between the maximum amount of work the engine can do and
the actual amount of work the engine actually did. The in-cylinder
pressure data is used to determine the maximum amount of work the
engine can do. The actual amount of work performed is calculated
form the output torque. The difference is caused by engine
inefficiencies, including those due to friction loss (total
friction work). The total friction loss includes the work loss due
to friction in the piston, valve train, bearings, oil seals, pumps
including oil, water and fuel pumps, alternator, and pumping
losses. The contribution of the piston ring coefficient of friction
to the total friction loss may be estimated from a comparison of
the piston assembly friction with the total friction loss (which is
dependent on the power output of the engine).
[0103] FIG. 20 is a graph of the absolute magnitude of the friction
in one engine cycle for coated and uncoated piston rings. After
normalization, it can be calculated that the coated piston ring
contributes to 18% of the total coefficient in the friction engine
test. In contrast, the uncoated piston rings contribute to 25% to
34% of the total coefficient of friction in two different
tests.
Durability Test
[0104] Based on the results of the friction engine test a coating
was applied to the top and second ring of the single cylinder oil
test engine using the conditions of sample 11. The test results
showed lower ring weight loss for both the coated top and second
ring. In addition, the mating surfaces of the cylinder liner
demonstrated lower wear as indicated by a 12 point wear step
measurement wherein wear is measured at 12 circumferential points
around the liner of the piston seen in FIG. 21a. The results of the
liner wear step measurements are shown in FIG. 21b. Although both
tests showed wear steps that are on the low end of what is
typically measured, the coated test still showed a 78% reduction in
average liner wear, as seen in FIG. 21c.
[0105] FIGS. 22a and 22b illustrate the amount of iron and titanium
present in engine oil over a period of 120 hours for the cast iron
baseline material and the coated ring as measured using inductively
coupled plasma analysis. As seen in FIG. 22a, the test results
indicate that iron concentrations for the coated and baseline
materials was similar and indicates normal overall engine wear for
both cases. FIG. 22b illustrates a steady accumulation of titanium
in the engine oil, which suggests a steady wear rate for the
coating throughout the entire test period as the only source for
the titanium was the Ti--Si--C--N coating.
Deposition Rates
[0106] The coating deposition rate may be found in Table 2
reproduced above. Generally, the deposition rate is in the range of
3.3 to 6.7 micrometers per hour. Where the reactive gas flow rate
of N.sub.2 and HMDSN are 45 sccm and 3 g/h, respectively, and the
flow rate of C.sub.2H.sub.2 in the range of 10 to 25 sccm, the
deposition rate is between 4.5 and 5.8 micrometers per hour. The
rate of deposition is much higher than most CrN coating rates.
Consequently, the deposition of the Ti--Si--C--N coatings herein
may be superior to the commercially used CrN production
coatings.
[0107] The foregoing description of several methods and embodiments
has been presented for purposes of illustration. It is not intended
to be exhaustive or to limit the claims to the precise steps and/or
forms disclosed, and obviously many modifications and variations
are possible in light of the above teaching. It is intended that
the scope of the invention be defined by the claims appended
hereto.
* * * * *