U.S. patent application number 13/652100 was filed with the patent office on 2013-04-25 for deposition system, method and materials for composite coatings.
The applicant listed for this patent is Vladimir E. BELASHCHENKO. Invention is credited to Vladimir E. BELASHCHENKO.
Application Number | 20130098267 13/652100 |
Document ID | / |
Family ID | 36090341 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098267 |
Kind Code |
A1 |
BELASHCHENKO; Vladimir E. |
April 25, 2013 |
Deposition System, Method And Materials For Composite Coatings
Abstract
A composite powder for a deposition of a composite coating
comprises a nonmetallic component and a metallic component, the
metallic component having an amorphous structure or a
nanocrystalline structure. The metallic component may include an
amorphous metallic alloy. The metallic alloy may include
constituents having the amorphous structure. The metallic component
may include a combination of the metallic alloy existing in the
amorphous state and constituents of the amorphous metallic alloy in
the amorphous state. The composite metal-ceramic powders are used
for depositing composite coatings on a selected surface. Disclosed
are several methods and systems for producing such composite
powders. Disclosed are also several methods and systems for
depositing composite coatings. Advantageously, the deposited
coatings exhibit high corrosion resistance, high wear resistance,
and excellent structural properties.
Inventors: |
BELASHCHENKO; Vladimir E.;
(Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BELASHCHENKO; Vladimir E. |
Waltham |
MA |
US |
|
|
Family ID: |
36090341 |
Appl. No.: |
13/652100 |
Filed: |
October 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12715796 |
Mar 2, 2010 |
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13652100 |
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11686813 |
Mar 15, 2007 |
7670406 |
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12715796 |
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PCT/US05/33203 |
Sep 16, 2005 |
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11686813 |
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60610472 |
Sep 16, 2004 |
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Current U.S.
Class: |
106/286.2 |
Current CPC
Class: |
H05H 1/42 20130101; C23C
24/04 20130101; C23C 4/06 20130101; C22C 29/08 20130101; C23C 4/134
20160101; Y10T 428/2982 20150115; Y10T 428/12181 20150115; C22C
1/1084 20130101; C22C 29/12 20130101; B22F 1/0096 20130101; C23C
4/04 20130101; C22C 29/16 20130101; C23C 4/067 20160101; B22F 3/115
20130101; C09D 7/61 20180101; C22C 29/14 20130101; B22F 9/002
20130101; C22C 29/04 20130101; C22C 29/02 20130101 |
Class at
Publication: |
106/286.2 |
International
Class: |
C09D 7/12 20060101
C09D007/12 |
Claims
1. A sprayed composite coating comprising: a nonmetallic component,
present in the range of about 40-84% by weight, wherein said
nonmetallic component is selected from the group consisting of
carbides, borides, nitrides, carbonitrides, oxides,
oxycarbonitrides or a combination thereof and has a particle size
of more than 0.2 microns; and an amorphous component comprising an
alloy including Fe, Co, Cu, or Ni, wherein said amorphous component
has less than about 50% crystallinity; and wherein at least some of
the particles of said amorphous component are in a form of a
plurality of splats of particles extended perpendicular to the
spray direction.
2. The composite coating of claim 1, further comprising a third
metallic component.
3. The composite coating of claim 2 wherein said third metallic
component comprises a crystalline metal comprising Co, Ni, Cr or
combination thereof.
4. The composite coating of claim 2 wherein said nonmetallic
component is imbedded in said third metallic component.
5. The composite coating of claim 1 wherein said nonmetallic
component is imbedded in said amorphous component.
6. The composite coating of claim 2, wherein said third metallic
component is less than about 50% by volume of the total metallic
phase.
7. The composite coating of claim 4, wherein particles of said
third metallic component imbedded with said nonmetallic component
are in a form of a plurality of splats of particles extended
perpendicular to the spray direction comprising third metallic
component with imbedded particles of said nonmetallic
component.
8. The composite coating of claim 1, wherein said amorphous
component alloy further comprises a transition metal selected from
the group consisting of Mo, Cr, W or combinations thereof present
at about 43% by weight or less.
9. The composite coating of claim 1, wherein said amorphous
component alloy further comprises an element selected from the
group consisting of C, Si, B, Mn or combinations thereof present at
about 14% by weight or less.
10. A method for spraying a composite coating comprising: supplying
a nonmetallic component, present in the range of about 40-84% by
weight, wherein said nonmetallic component is selected from the
group consisting of carbides, borides, nitrides, carbonitrides,
oxides, oxycarbonitrides or a combination thereof and has a
particle size of more than 0.2 microns; supplying an amorphous
component comprising an alloy including Fe, Co, Cu, or Ni, wherein
said amorphous component has less than about 50% crystallinity;
wherein particles of said nonmetallic and said amorphous components
are mixed together to provide a powder having particle size in the
range of about 15 to 160 microns; forming said composite coating
from said nonmetallic component and amorphous component wherein at
least some of the particles of said amorphous component are in a
form of a plurality of splats of particles extended perpendicular
to the spray direction.
11. The method of claim 10, further comprising a third metallic
component.
12. The method of claim 11 wherein said third metallic component
comprises a crystalline metal comprising Co, Ni, Cr or combination
thereof.
13. The method of claim 11 wherein said nonmetallic component is
imbedded in said third metallic component.
14. The method of claim 10 wherein said nonmetallic component is
imbedded in said amorphous component.
15. The method of claim 11, wherein said third metallic component
is less than about 50% by volume of the total metallic phase.
16. The method of claim 13, wherein particles of said third
metallic component imbedded with said nonmetallic component are in
a form of a plurality of splats of particles extended perpendicular
to the spray direction comprising third metallic component with
imbedded particles of said nonmetallic component.
17. The method of claim 10, wherein said amorphous component alloy
further comprises a transition metal selected from the group
consisting of Mo, Cr, W or combinations thereof present at about
43% by weight or less.
18. The method of claim 10, wherein said amorphous component alloy
further comprises an element selected from the group consisting of
C, Si, B, Mn or combinations thereof present at about 14% by weight
or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 12/715,796 filed Mar. 2, 2010, which is a continuation of U.S.
application Ser. No. 11/686,813 filed on Mar. 15, 2007, now U.S.
Pat. No. 7,670,406 issued on Mar. 2, 2010, which is a continuation
of PCT/US05/033203 filed on Sep. 16, 2005, which claims the benefit
of U.S. Provisional Application 60/610,472 filed on Sep. 16, 2004
entitled "Deposition System, Method and Materials for Composite
Coatings, all of which are incorporated by reference.
TECHNICAL FIELD
[0002] The present invention is directed to composite powders for
deposition of high quality composite coatings, and systems and
methods for producing such powder.
BACKGROUND
[0003] Metal parts of various industrial machines or
general-purpose machines are required to have various properties
such as impact resistance, corrosion resistance and wear resistance
depending upon their respective purposes. However, in many cases,
the metal (or substrate) constituting such metal parts cannot
adequately satisfy the required properties by itself, and it is
therefore often subjected to surface modification, particularly by
forming a coating or deposition on the substrate surface.
[0004] Varieties of powder compositions for different deposition
processes are known and described in publications. Mainly, the
powders comprise particles of a nonmetallic/ceramic compound like
tungsten carbide, chromium combined with a metal such as Ni, Cr, Co
or an alloy containing such a metal as a binder, to form a
ceramic/metal composite material. Conventional composite materials
based on metallic and nonmetallic compounds are presently made by
different manufacturers like Praxair, Sulzer-Metco, etc. A very
brief list of some of these compounds is the following: WC-12Co;
WC-17Co; WC-10Co-4Cr; Cr.sub.3C.sub.2-25NiCr; WC-10Ni. The metallic
component of a composite metal-ceramic (cermet) is in a
thermodynamically stable state and represented by a metal or an
alloy having a crystalline structure.
[0005] More complex compositions of cermet powders for surface
modification are also well known. Such compositions, comprising
nitrides, carbonitrides, borides (for example, titanium
carbonitride) and multicomponent metallic alloys (for example,
CoCrAIY, FeCrAIY, and so on) have not yet found wide
application.
[0006] Thermal spray coating typically follows one of several
general schemes disclosed in literature and patents. In a first
method, particles used to coat a substrate may be heated so that
their temperature when they contact the substrate is greater than
their melting temperature. This case is generally typical for
conventional flame spraying, atmospheric plasma spraying (APS) and
low pressure plasma spraying (LPPS). Because the particle is in a
melted or fused state and traveling at a relatively high velocity
when it contacts the substrate, splashing of the melted or fused
particles often occurs during the collision and interaction with
the substrate. Melting of the nonmetallic component of a composite
powder may cause its undesirable decomposition and phase
transformation as well.
[0007] As shown in FIG. 12, a normal component of pressure may
exist only on a surface area underneath the particle having a
diameter D.sub.x, which is equal or smaller than diameter D of the
sprayed particle. In this case, good bonding may only develop in
the area with diameter D.sub.x underneath the particle. The
particle will splash, and the portion outside diameter D.sub.x, may
not make proper contact with the substrate to enable good bonding
to it. Splashing often results in voids and excessive surface area
of the splashed particles. These characteristics may, consequently,
result in excessive oxidation, low wear, corrosion and erosion
resistance of the coated object. Higher impact velocities may
result in the higher intensity of the impact, splashing, and a
greater area of the particle extending outside of diameter
D.sub.x.
[0008] According to a second method, thermal spraying may take
place under conditions such that
E.sub.Tp+V.sub.p.sup.2/2>E.sub.m, where E.sub.Tp+V.sub.p.sup.2/2
is the total energy of the particle upon collision with the
substrate; it is the thermal energy of the particle upon contact
with the substrate. E.sub.m is the energy needed to heat and melt
all the components of the particle (the latent heat of melting is
included in E.sub.m). T.sub.p is the temperature of the particle
upon contact with the substrate. V.sub.p is the velocity of the
particle upon contact with the substrate, and T.sub.m is the
melting temperature of the particle's nonmetallic component. Such a
scheme is often termed "impact fusion" and was disclosed in U.S.
Pat. No. 5,271,965, which is incorporated by reference. While the
intensity of splashing may be lower than that experienced in the
first spraying scheme, splashing of the coating particles is
generally experienced during impact fusion. Splashing that occurs
during impact fusion results in all of the same consequences
discussed above.
[0009] According to a third coating method, particles may be heated
to a temperature sufficiently low to prevent thermal softening of
sprayed particles. The particles heated in this manner may be
applied to a substrate at high velocities. This coating scheme may
generally only be applicable for use with coating materials having
very low yield stress, for example, in a general range of about 200
MPa or less. Amorphous and nanocrystalline alloys considered in the
disclosure have significantly higher yield strength which is in the
range of about 500-1200 MPa at room temperature. However, this
third coating scheme may have a very low efficiency when spraying
the metal-ceramic composite powders.
[0010] Disadvantages of prior art composite materials are partially
related to the metallic compounds or binders, which are based on
metals like Ni and Co, and the conventional crystalline alloys with
other metals like Cr, etc. In some cases these types of binders do
not provide desirable corrosion resistance, bonding with
nonmetallic components of a composite material, wear and erosion
resistance, toughness and some other properties determining
performance of the composite material. Notably, Co and Ni based
alloys are expensive. The current deposition processes allow one to
deposit the conventional metal-ceramic composites listed above, as
well as amorphous and nano- or microcrystalline metallic alloys,
more or less successfully.
[0011] However, there is still a need for novel metal-ceramic
composite coatings and depositions containing amorphous and
nanocrystalline metallic components.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to composite metal-ceramic
powders used for depositing composite coatings on a selected
surface. Several embodiments of the present invention are directed
to methods and systems for producing such composite powders.
Several embodiments of the present invention are also directed to
methods and systems for depositing the metal-ceramic composite
powders to form coatings. Advantageously, the deposited coatings
exhibit high corrosion resistance and excellent structural
properties.
[0013] According to one important aspect, a composite powder for a
deposition of a composite coating comprises a nonmetallic component
and a metallic component, the metallic component having an
amorphous structure.
[0014] Preferably, the metallic component may include an amorphous
metallic alloy. The metallic alloy may include constituents having
the amorphous structure. The metallic component may include a
combination of the metallic alloy existing in the amorphous state
and constituents of the amorphous metallic alloy in the amorphous
state. The metallic alloy may be in the form of a continuous matrix
having the amorphous structure. The metallic component may include
a combination of the metallic alloy and an alloy having continuous
matrix with an amorphous structure. The metallic alloy may also
include constituents having a nanocrystalline structure.
[0015] According to another important aspect, a composite powder
for a deposition of a composite coating comprises a nonmetallic
component and a metallic component, the metallic component having a
nanocrystalline structure.
[0016] Preferably, the metallic component includes a metallic
alloy. The metallic alloy may include some constituents having an
amorphous structure.
[0017] Preferably, when preparing the composite powders, the ratio
of the nonmetallic component and the metallic component may be
adjusted for use in thermal spraying deposition, in plasma transfer
arc deposition, in laser cladding deposition, or in weld overlay
deposition. Preferably, when preparing the composite powders, the
ratio of the nonmetallic component and the metallic component may
be adjusted to obtain a coating having a selected wear resistance,
a selected oxidation resistance, a selected corrosion resistance, a
selected toughness, a selected thermal conductivity, or a selected
stress property.
[0018] Preferably, when preparing the composite powders, the
particle size of the nonmetallic component and the metallic
component may be adjusted for use in thermal spraying deposition,
in plasma transfer arc deposition, in laser cladding deposition, or
in weld overlay deposition. Preferably, when preparing the
composite powders, the particle size of the nonmetallic component
and the metallic component may be adjusted to obtain a coating
having a selected wear resistance, a selected oxidation resistance,
a selected corrosion resistance, a selected toughness, a selected
thermal conductivity, or a selected stress property.
[0019] Preferably, when preparing the composite powders, the
chemical composition of the nonmetallic component or the metallic
component, may be separately, or together, selected to obtain a
deposited coating having a selected wear resistance, a selected
oxidation resistance, a selected corrosion resistance, a selected
toughness, a selected thermal conductivity, or a selected stress
property.
[0020] According to yet another important aspect, a method of
preparing a composite powder for a deposition of a composite
coating onto a substrate, comprising: providing a nonmetallic
component, providing a metallic component having an amorphous
structure (or a nanocrystalline structure), and creating a
composite of the nonmetallic component and the metallic
component.
[0021] According to yet another important aspect, an apparatus for
depositing a composite coating includes a deposition gun and a
feeder constructed to provide a composite powder comprising a
nonmetallic component and a metallic component having an amorphous
structure or a nanocrystalline structure.
[0022] The apparatus may include a single feeder, or two feeders
being constructed to provide separately components of the composite
powder, at least some of the components being separately delivered
from the powder injectors into the deposition gun.
[0023] Optionally, the first of the powder feeding modules may be
constructed to provide the nonmetallic component and the second of
the powder feeding modules may constructed to provide the metallic
component thereby achieving a selected powder mixture inside the
apparatus. The metallic component may include an amorphous metallic
alloy. The metallic alloy may include constituents having the
amorphous structure. The metallic component may include a
combination of the metallic alloy existing in the amorphous state
and constituents of the amorphous metallic alloy in the amorphous
state.
[0024] According to a preferred embodiment, the novel composite
metal-ceramic powders have an amorphous metallic binder to provide
coatings with a combination of low cost, high hardness, high
corrosion and oxidation resistance as well as high deposition
efficiency. Preferably, the coatings are deposited using the
thermal spray process. Additional embodiments of the present
invention include thermal spray processes and thermal spray
equipment optimized for specific composite metal-ceramic powders
for producing the coatings.
[0025] Preferably, the novel composite metal-ceramic powders are
used for surface modification of various substrates that require
high impact resistance, excellent wear resistance, and excellent
corrosion and erosion resistance even under high temperature.
Preferably, the coatings are deposited using a deposition apparatus
which generally provides a stream of gas having a desired
temperature and velocity profile. The deposition apparatus includes
a feeding module for the introduction of the powder or particulate
material into the gas stream and deposition onto the desired
surface. Preferably, the deposition apparatus is a high velocity
thermal spray (HVTS) apparatus for spraying composite metal-ceramic
powders. Alternatively, the deposition apparatus is selected from
the high velocity oxygen fuel (HVOF) apparatuses like JP 5000
manufactured by Praxair-Tafa, Diamond Jet manufactured by Sulzer
Metco, Jet Kote manufactured by Stellite Coatings, Inc., or the
deposition apparatuses described in U.S. Pat. No. 5,932,293. Other
deposition apparatuses and methods may be used as well. The
technology provides very good cohesion/adhesion between ceramic
components and amorphous and/or nanocrystalline metallic components
during the deposition process and coating formation.
[0026] According to one aspect of the invention, the composite
metal-ceramic powder includes at least two (2) components, wherein
the first component is a nonmetallic/ceramic component, and the
second component is a metallic alloy able to exist at least
partially in an amorphous state. The composite metal-ceramic powder
may also include a combination of metals, or metallic alloys
capable to form an amorphous alloy, and metals or metallic alloys
in a microcrystalline (nanocrystalline) state. The
nonmetallic/ceramic component is made of at least one compound
selected from the group consisting of carbides, borides, nitrides,
carbonitrides, oxides, oxycarbonitrides, or any combination of
these. The metallic component is at least partially amorphous or
has a microcrystalline (nanocrystalline) structure. The metallic
component may be chosen from amorphous and nanocrystalline alloys
(for example, those disclosed in U.S. Pat. Nos. 6,258,185 and
6,689,234, which are incorporated by reference). The composite
powder may also include one or several additional components, for
example, an additional crystalline metallic component. The
additional metallic component may include Cobalt, Nickel, Chromium
and combinations thereof.
[0027] In optimal composite powders, the amorphous metal alloy
comprises no less than 50% by volume of the total metallic phase of
the composite powder. Furthermore, the composite powder may be
characterized by the fact that the size of the discrete particles,
or that of the discrete agglomerates of particles, of the metallic
component is less than 100 .mu.m, more preferably less than 45
.mu.m and most preferably within 15 to 45 .mu.m.
[0028] Moreover the novel composite powders may be characterized by
the fact that discrete particles of the nonmetallic component are
imbedded into the matrix of the metallic component. The composite
coating may also contain the amorphous metal alloy that includes a
crystalline phase with crystals no larger than 200 nm, or
preferably no larger than 100 nm.
[0029] The composite powder may have different particle size
distribution, which is dictated by deposition method. According to
one embodiment, particle size may be in the range of 40 to 160
.mu.m. According to another embodiment, particle size may be in the
range of 20 to 106 .mu.m. According to a third embodiment, particle
size range may be 15 to 53 .mu.m and 15 to 45 .mu.m. Other ranges
of particle size may be produced satisfying requirements for a
certain deposition quality and capability of a deposition
process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 illustrates a V-shape blender for mixing components
to prepare a deposition material.
[0031] FIG. 2 illustrates different factors taken into account when
selecting a ratio of metallic and nonmetallic components of the
deposition material.
[0032] FIG. 3 is a schematic illustration of an embodiment of an
HVTS apparatus.
[0033] FIG. 4 is an illustration of the rectangular forming block
for the HVTS apparatus.
[0034] FIG. 5 illustrates an embodiment of the apparatus including
a mixing chamber and a forming module with axial powder
feeding.
[0035] FIG. 6 illustrates an embodiment of a mixing chamber and a
forming module with the attached barrel and radial powder feeding
in a low pressure zone.
[0036] FIG. 7 is an optical micrograph showing a microstructure of
a coating sprayed using a blend of WC-10Co-4Cr with 10% SHS 7170 by
weight.
[0037] FIG. 8 is an optical micrograph showing a microstructure of
a coating sprayed using a blend of WC-10Co-4Cr with 15% SHS 7170 by
weight.
[0038] FIG. 9 is an optical micrograph showing a microstructure of
a coating sprayed using a blend of WC-10Co-4Cr with 50% SHS 7170 by
weight.
[0039] FIG. 10 is an optical micrograph showing a microstructure of
a coating sprayed using a blend of Cr.sub.3C.sub.2-25NiCr with 27%
SHS 7170 by weight.
[0040] FIG. 11 is an optical micrograph of a sprayed coating
showing an indentation at the contact of the WC-10Co-4Cr and SHS
7170 particles for the purpose of the DPH300 measurement.
[0041] FIG. 12 is a schematic illustration of a melted particle
interaction with a substrate at deposition.
[0042] FIGS. 13A, 13B, and 13C are optical micrographs showing
microstructures of coatings based on W-balance; Cr 4%; Co 10%; C
5.3% after 5 hours of oxidation at 750.degree. C., wherein the
coating on FIG. 13A includes 10% SHS, the coating of FIG. 13B
includes 50% SHS, and the coating of FIG. 13C includes no SHS.
[0043] FIGS. 14A and 14B are optical micrographs showing
microstructures of coatings based on W-balance; Cr 4%; Co 10%; C
5.3% after 5 hours of oxidation at 850.degree. C., wherein the
coating on FIG. 14A includes 50% SHS, and the coating of FIG. 14B
includes no SHS.
[0044] FIG. 15A is an optical micrograph showing microstructures of
coatings made with a composite powder made of 65% 1350 VM and 35%
SHS 7574 having particle size of 20-25 .mu.m.
[0045] FIG. 15B is an optical micrograph showing microstructures of
coatings made with a composite powder made of 65% 1350 VM and 35%
SHS 7574 having particle size of 20-45 .mu.m.
[0046] FIG. 16 is an optical micrograph showing microstructures of
coatings made with a composite powder made of 50% 1350 VM and 50%
SHS 7170 sprayed using separate powders fed using two
injectors.
[0047] FIG. 17A is an optical micrograph showing an indentation
into a sprayed coating made with a composite powder made of 65%
1350 VM and 35% SHS 7170.
[0048] FIG. 17B is an optical micrograph showing an indentation
into a sprayed SHS 7170 coating.
[0049] FIG. 18 is an optical micrograph showing microstructures of
coatings made with a composite powder made of 80% WC and 20% SHS
7170.
[0050] FIG. 19 includes Tables 1 and 2, wherein Table 1 shows the
compositions of deposited coatings and deposition parameters, and
Table 2 provides a summary of the deposition efficiency and the
test results of the coatings described in Table 1.
[0051] FIG. 20 includes Tables 3 and 4, wherein Table 3 shows the
compositions of deposited coatings, and Table 4 provides a summary
of the sprayability results of the coatings described in Table
3.
[0052] FIG. 21 includes Tables 5 and 6, wherein Table 5 provides a
summary of test data performed on the coatings described in Table
3, and Table 6 summarizes the results of the G-65 tests performed
on the coatings described in Table 3.
[0053] FIG. 22 includes Tables 7 and 8, wherein Table 7 provides a
summary of the erosion tests performed on the coatings described in
Table 3, and Table 8 provides a summary of the deflection tests
performed on the coatings described in Table 3.
DESCRIPTION OF THE OF THE PREFERRED EMBODIMENTS
[0054] FIG. 1 illustrates mixing of the powders in a powder mixer
such as a V-shaped blender. The V-shape blender is very popular in
a wide variety of industries and manufacture, for example, by
Gemco. The effective blending is achieved by the constant tolling
action of the classic tumble blender. Each leg of the V-shape works
independently to efficiently achieve a uniform blend. The precise
mixing action results in blend variations of about 1-2%. Each
cylindrical leg has an access for easy material loading and
cleaning.
[0055] After preparation, a cermet powder includes at least two (2)
components, wherein the first component is a nonmetallic
(hereinafter, the ceramic component), and the second component is a
metallic alloy existing or able to exist at least partially in an
amorphous state. The second component of the composite
metal-ceramic (cermet) powder may also include a combination of
metals, or metallic alloys capable to form, at least partially, an
amorphous alloy, and metals or metallic alloys in a
microcrystalline (nanocrystalline) state with crystals the size of
less than 200 nm.
[0056] The composite cermet powders are used for deposition of
composite coatings. Prior to the deposition (or in some
embodiments, during feeding just before the deposition) the cermet
powder is manufactured using a variety of processes providing at
least one nonmetallic component and at least one metallic
component.
[0057] The composite thermal spray powder can be prepared by mixing
or blending the discrete particles of the nonmetallic component
and/or cermet particles with the particles of the metallic
component prepared by, for example, gas atomization, the "cast and
crush technique," or by a spray-drying and sintering technique, to
form amorphous particles or an amorphous metallic alloy. The
created particles are discrete particles, discrete agglomerates of
particles or a combination thereof.
[0058] FIG. 2 illustrates different factors taken into account when
selecting a ratio of metallic and nonmetallic components for the
composite powder. As described below, a ratio may differ depending
on the deposition technique, deposition parameters, and the desired
properties of the produced coating. The proper ratio of components
can be automatically delivered to a powder-feeding module (e.g., a
powder injector) of a spray gun. The components may also be
separately delivered to separate powder injectors of a single
deposition gun, wherein the proper mixture is achieved by adjusting
the feeding rates of each powder injector.
[0059] According to one preferred embodiment, the composite thermal
spray powder is prepared by a mechanical mixing or blending
starting from commercially available nonmetallic powders and a
powder of an amorphous metallic alloy. The amorphous metallic alloy
is prepared by, for example, gas atomization, water atomization,
comminuting of a bulk alloy or similar methods. The composition of
the amorphous metallic alloy is selected according to the coating
deposition method. Preferably, the content of the nonmetallic
component is within the range of 84 to 40% by weight. The
composition of the amorphous metallic coating is preferably as
described in U.S. Pat. Nos. 6,258,185 and 6,689,234, which are
incorporated by reference.
[0060] According to another embodiment, the composite thermal spray
powder is produced by making a dispersion of particles of the
nonmetallic component in a melt of metals capable to form the
amorphous metallic alloy upon quenching, following by rapid
solidification of the dispersion. The rapid solidification could be
performed, for example, by gas atomization or by water atomization
or by casting/quenching. Gas atomization results in powders, which
should provide desirable size and size distribution of the
particles for use in this application. The casting/quenching
process results in a bulk material in the form of, for example,
ribbons, or stratums, that are to be crushed. Crushed product is to
be comminuted by applying, for example, wet or dry ball milling,
jet milling, or impact milling. The comminuted product should be
then classified according to the application of the resulting
thermal spray powder.
[0061] The composite powders produced by rapid solidification
technique, as described above, are composed of solid (not porous)
discrete particles of the amorphous metallic alloy with uniformly
dispersed discrete particles of nonmetallic component imbedded in
the metallic matrix.
[0062] According to yet another embodiment, the composite thermal
spray powder is prepared through a spray-drying and sintering
technique. In such a technique a dispersion of discrete particles
of nonmetallic component and discrete particles of metallic
component is first prepared in water or in an organic solvent
(e.g., an alcohol) containing an organic binder (e.g., polyvinyl
acetate or polyvinyl alcohol). If needed, an inhibitor of corrosion
could be added to the dispersion, or slurry, to prevent reaction of
the metallic components with water or with the solvent. This slurry
is formed into a spherical agglomerated powder by means of a spray
drier, for example. Then the spray-dried powder is subjected to
classification for the purpose of obtaining a spray-dried powder
having a particle size distribution required for the thermal
spraying or other deposition conditions for the type of the
spraying or deposition apparatus to be used.
[0063] To provide appropriate toughness of thus prepared
spray-dried and not sintered powders, the content of organic binder
in the slurry could be increased up to 5% by weight with respect to
the content of solids, if needed. The spray-dried powder could be
subjected to thermal treatment (sintering) to remove the organic
binder from the agglomerated powder and for the purpose of
imparting a proper mechanical strength to the agglomerated powder
particles. The sintering temperature should be chosen according to
the composition of the metallic component and should be lower than
that of the melting point of most refractory metallic constituents
of the spray-dried powder. There are no specific limitations on the
lowest sintering temperature but appropriate mechanical strength of
the sintered particles should be provided. The sintering should be
performed in an atmosphere or environment preventing oxidation of
the metallic components, such as in a vacuum, in argon, or in
hydrogen.
[0064] For the successful performance of the spray drying process
it is required that the size of the particles of the solids in the
slurry should be less than about 10 .mu.m. The metallic components
in this process could be in the form of powders of individual
metals, powders of partial metal alloys (for example,
Ferrochromium, Ferromolybdenum, Ferroniobium, etc.), and/or a
combination of these. Powders of individual metals having a
particle size of less than 10 .mu.m are commercially available. As
for amorphous metallic alloys which are available in the form of
ribbons, stratums or atomized powders, they are to be comminuted by
applying such techniques as dry/wet ball milling, jet milling,
impact milling etc., though cryogenic milling is preferable. By
applying cryogenic milling, the amorphous state of the alloy will
be preserved in the fine comminuted powder.
[0065] According to yet another embodiment, the composite powder is
prepared through a sintering and crushing technique. In such a
technique, a dry blend of the components is prepared using a known
technique and apparatus, such as a ball mill, double cone blender,
ribbon blender, etc. The thus prepared blend of components is then
loaded into crucibles, sintered and the obtained bulk composite
material is then mechanically crushed by means of a known technique
such as ball milling, impact milling, etc. Then, the classification
is carried out for the purpose of obtaining a composite powder
having a particle size distribution required upon the deposition
conditions or the type of the deposition apparatus to be used. The
sintering temperature and atmosphere should be chosen according to
that described for the sintering of spray-dried powders.
[0066] The composite powders produced by the spray drying, or the
sintering and crushing technique, as described above, are composed
of porous (spongy) discrete agglomerates of particles of the
amorphous metallic alloy with discrete particles of the nonmetallic
component dispersed through the metallic matrix.
[0067] The composite powders, manufactured as described above, are
deposited to form coatings, for example, as follows.
[0068] FIG. 3 illustrates a high velocity thermal spray (HVTS)
apparatus including a heating module M1 that provides high
temperature gases at pressure Pcc. The gas pressure Pcc in the
heating module may be about 3-4 times, or more, greater than
ambient pressure. The gas at the outlet of the heating module has a
temperature Tcc.
[0069] The HVTS apparatus may also include a mixing module M2
constructed to combine the high temperature gas generated by the
heating module with lower temperature compressed gas. Combining the
high temperature gas from the heating module with compressed gas
allows the temperature of the gas stream to be controlled and/or
adjusted to a desired or predetermined temperature.
[0070] The HVTS apparatus may also include a forming module M4,
which may form the stream of gases from the mixing module. That is,
the forming module may control the pressure and/or velocity
profiles of the gases from the mixing module. The forming module
preferably accelerates the gases from the mixing module to provide
a sonic or supersonic jet of gas.
[0071] The HVTS apparatus may also include a powder-feeding module
M3, which may feed the powder to be sprayed by the HVTS apparatus
into the gas stream produced in the mixing module and/or combustion
and mixing modules. The powder introduced in the feeding module may
be sprayed onto a substrate to form a coating, to shot peen the
substrate or a coating thereon, etc.
[0072] The modular design of the HVTS apparatus allows separate
modules to be assembled to provide desired performance parameters
for the HVTS apparatus as a whole. The separate modules may be
assembled, for example, for use with a particular heating module
design, spraying materials and/or requirement of coatings to be
sprayed. The heating module of the HVTS apparatus may be provided
as an oxidizer-fuel combustion module, a plasma torch, or a
resistance heater. Other configurations may also be achieved which
are consistent with the present disclosure.
[0073] In some situations, it may be desirable to operate the
heating and mixing modules at a pressure, Pcc, greater than or
equal to 5-6 times ambient pressure; in others, Pcc should be
greater than or equal to 9-10 times ambient pressure, or greater
than or equal to 14-15 times ambient pressure. Such operating
pressures Pcc may allow coating particles to be accelerated up to a
velocity that may approach, or even exceed, about 1,000 m/s. The
exact velocity achieved by the coating particles may vary greatly,
however, depending upon the pressure, gas temperature, particle
size, etc. Accordingly, the velocity experienced by the coating
particles may range from hundreds of meters per second to much
greater.
[0074] Referring to FIG. 3, an HVTS apparatus 100 includes a
heating module M1, a mixing module M2, a forming module M4, and a
powder-feeding module M3. While we refer to this apparatus as an
HVTS apparatus, the apparatus may be configured as a HVOF (high
velocity oxidizer-fuel) apparatus, a high velocity high pressure
plasma apparatus, and/or similar systems producing an output
including a stream of heated gaseous products. While the HVTS
apparatus 100 is schematically delineated as four modules M1, M2,
M3, M4, it may include additional features or modules.
Additionally, it is not necessary within the present disclosure
that the four modules M1, M2, M3, and M4 be physically discrete or
separable components. For example, the powder-feeding module M3 may
be provided as a part of the forming module M4 or may be disposed
within the forming module. Moreover, the various modules M1, M2,
M3, and M4 may be disposed in a different arrangement relative to
one another. For example, in an embodiment in which the
powder-feeding module M3 is not provided as part of, or integrated
with, the forming module, the powder-feeding module may be disposed
downstream of the forming module M4, rather than upstream of the
forming module M4 such as shown in FIG. 3.
[0075] The forming module M4 may include a converging zone 204 in
which the diameter of the gas passage is reduced. Converging zone
204 may terminate in a throat or orifice 28. From throat 28, the
diameter of the gas passage may increase through an expansion zone
29. The increasing diameter of the gas passage in expansion zone 29
may cause the stream of gas to accelerate.
[0076] As mentioned above, according to one embodiment herein, the
heating module M1 may be capable of operating at pressures (Pcc)
that are in the range of about 3-4 times greater than ambient
pressure to 15 times ambient pressure or above. The ambient
pressure may range from greater than, equal to, or below
atmospheric pressure. The gases from the heating module may have a
temperature Tcc, measured at the exit of heating module M1.
[0077] Forming module M4 may have axial symmetry, e.g. it may have
a circular cross section and a throat diameter D.sub.t and an
expansion zone exit diameter D.sub.e. It may, however also be
rectangular, as illustrated in FIG. 4.
[0078] Heating module M1 may include any variety of apparatuses
capable of providing a gas stream having a pressure Pcc and
temperature Tcc at the exit of heating module M1. According to
various embodiments, heating module M1 may include combustion
modules wherein the gas stream may include combustion gases or
products. Examples of combustion type heating modules may include
oxygen-fuel combustion chambers, such as may be used with
conventional high velocity oxygen-fuel thermal spraying
apparatuses. Heating module M1 may also include a resistance
heating module capable of heating a gas introduced into the module.
In other embodiments, heating module M1 may include a plasma
module. Heating module M1 may also be a plasma torch, or a
combustion device.
[0079] FIGS. 5 and 6 illustrate an embodiment of an HVTS device
including a mixing chamber 160 (M2). The mixing chamber 160 (M2)
may be directly or indirectly coupled to the initial plasma-forming
module 142 of a plasma torch. Consistent with the illustrated
embodiment, mixing chamber 160 (M2) may include one or more
passages 158 that may be coupled to a source of pressurized gas at
a predetermined temperature. According to one embodiment, the
pressurized gas may be at a temperature lower than the temperature
of the gas entering mixing chamber 160 (M2) from plasma-forming
module 142. The pressurized gas may be, for example, at a
temperature much lower than the temperature of the gas entering the
mixing chamber 160 from the plasma-forming module 142. Suitable
pressurized gases may include Nitrogen, Helium, Argon, air and
mixtures thereof, or various other gases. Such gases when released
from a pressurized state may naturally achieve a reduced
temperature, thereby eliminating the need for any temperature
conditioning apparatus. However, the use of temperature
conditioning apparatuses, either for cooling or heating the
pressurized gas, is contemplated herein.
[0080] As shown, mixing chamber 160 (M2) may include at least one
passage 154 that may be connected to a pressure sensor (not shown),
which may be provided as part of a feedback circuit that may be
used to control the pressure in the mixing chamber 160. A plasma
jet may exit the plasma channel 152 and may be mixed together with
the pressurized gases supplied through passages 158. Mixing of the
gases may provide a desired temperature of gases exiting the mixing
chamber 160. The mixture of gases may pass from the mixing chamber
160 into a converging zone 204, a throat 28 and an expansion zone
29 of a forming module. The forming module may accelerate the
mixture of gases up to a desired velocity. According to one
embodiment, the forming module may accelerate the mixture of gases
up to a supersonic velocity. The mixing chamber 160 may be water
cooled using passages 164.
[0081] The embodiment illustrated in FIG. 5 depicts an axial powder
feeding system. An axial powder feeding system may advantageously
be used in combination with a right angle heating module, i.e., a
heating module having a gas outlet oriented at an angle to the
outlet of mixing chamber 160. A modified configuration of the axial
powder-feeding system may also be used in connection with an
embodiment in which the heating module is oriented axially with the
outlet of mixing chamber 160. FIG. 5 illustrates the option when
mixing chamber 160 is connected with plasma-forming module 142,
which is located generally 90 degrees relative to the axis of
mixing module 160.
[0082] Referring still to FIG. 5, the composite powder or
particulate material may be fed through a fitting 166 into a powder
channel formed by a powder injector holder 174. Powder injector 162
is connected with the holder 174. Powder injector holder 174, as
well as powder injector 162, may be water cooled. The length of the
powder injector holder 174 may be adjusted providing a desired
position of the powder injector exit within mixing chamber 160 or
forming module. The exit of powder injector 162 may be located
inside mixing chamber 160, or in the converging zone 204 of the
forming module. The exit of the powder injector 162 could also be
located in throat 28 of the forming module, or in the expansion
zone 29 of the forming module.
[0083] FIG. 6 illustrates another embodiment of an HVTS apparatus
including the mixing chamber and the forming module and having a
radial powder feeding in a low pressure zone. Expansion zone 29 of
the forming module may be connected with a barrel that serves to
extend the dwell time of particles introduced into the gas stream
exiting the forming module. The increase in the dwell time of the
particles may also provide an increase in the temperature and
velocity of the particles as they exit the barrel. The
powder-feeding module (not shown) may be coupled to powder
injectors, such as the radial powder injectors 32 of the embodiment
shown in FIG. 6. The powder injectors 32 may feed powder into the
gas stream from mixing chamber 160 before, during, or after the gas
stream has entered the barrel. According to one embodiment, the
powder injectors 32 may be located in a low pressure zone of the
gas stream. Locating the powder injectors 32 in this manner may
allow the use of a low pressure powder-feeding module.
[0084] According to another embodiment, the HVTS apparatus may
include two or more separate powder-feeding modules (not shown).
Each powder-feeding module is coupled to a powder injector, such as
the radial powder injectors 32 shown in FIG. 6. Each powder
injector provides one component of the composite powder formed
inside the low pressure zone. In the present description the term
"composite powder" includes powders having two or more components
delivered separately into a deposition gun as long as the deposited
film includes these components, as described below.
[0085] The HVTS apparatus may include numerous other combinations
of heating modules, forming modules, barrels, etc., which may be
used in the context of the present disclosure.
[0086] In general, the novel composite powders are deposited for a
coating using any of the well known deposition methods, such as
weld overlay, laser cladding, plasma transfer arc (PTA), and
thermal spray to deposit coating on different substrates. Suitable
thermal spraying methods include (but are not limited to) the
processes of atmospheric plasma spray; low pressure plasma spray;
high pressure and high velocity plasma spray, flame spray; high
pressure and high velocity processes based on combustion of an
oxidizer and a fuel; detonation process known as D-gun; and
processes known as Cold Spray.
[0087] Each particular method may need a specific powder size to
efficiently deposit high quality coatings. For example, PTA may
need powder with particle sizes within 40 to 160 .mu.m; plasma
spraying may need powder with particle sizes within 20 to 106
.mu.m; HVOF may need powder with particle sizes within 15 to 53
.mu.m or within 15 to 45 .mu.m. Moreover, each particular torch
delivering deposition for a particular application may need wider
or narrower powder size distribution.
[0088] According to one embodiment, thermal spraying is used to
deposit a coating on a substrate. The method includes feeding a
powdered coating material (hereinafter "powder") into a heated
stream of gas or plasma. The heated stream of gas or plasma may be
used to direct the powder at a substrate to be coated. The heated
stream of gas or plasma may heat the particles of powder up to an
average particle temperature T.sub.p at the moment of collision
with the substrate. Furthermore, the heated stream of gas or plasma
may accelerate the particles of powder to an average particle
velocity V.sub.p at the moment of collision with the substrate.
Upon collision with the substrate, the particles of powder may have
a total specific energy E.sub.p expressed by Equation (1)
E.sub.p=E.sub.Tp+V.sub.p.sup.2/2<E.sub.m (1)
where E.sub.Tp is a specific thermal energy of a particle that
collided with the substrate; E.sub.m is the specific energy needed
to heat and melt all components of a particle at the temperature
T.sub.m (the latent heat of melting of each component of a
composite material is included in E.sub.m); T.sub.p is the
temperature of the particle upon contact with the substrate;
V.sub.p is the velocity of the particle upon contact with the
substrate; and T.sub.m is the melting temperature of the particle's
nonmetallic component.
[0089] A result of the condition E.sub.p<E.sub.m, expressed by
Equation (1), it may be that a nonmetallic component of the
particle may not be melted upon colliding with the substrate.
Metallic components of a particle may be melted. A metallic
component that is melted may result in a minor splashing of the
metallic component. Melting of a metallic component may cause some
tensile stresses in deposition as well. However, shot peening and
densification effect of an unmelted nonmetallic component may
minimize the negative effect of splashing and tensile stresses
caused by metallic material shrinkage during solidification and
cooling. Melted metallic components form thin lamellas and provide
continuous anticorrosion protection.
[0090] If all components of the particle are not melted upon
colliding with the substrate, the particle may not splash as a
result of the collision. While the particle may not be melted upon
colliding with the substrate, the particle temperature T.sub.p at
impact may still be above the brittle-ductile transition
temperature of the metallic component of the particle. Allowing
T.sub.p to be above the brittle-ductile transition temperature may
avoid disintegration of spraying particles as a result of the
collision of the particles against the substrate.
[0091] A coating may also be sprayed under conditions where small
metallic components, for example, below 25 .mu.m, are melted and
metallic components of a larger size are not melted but are,
however, above the brittle-ductile transition temperature.
[0092] During collision, energy may be dissipated and heat
transferred into the substrate. This energy dissipation and heat
transfer may be characterized as energy loss .DELTA.E. Therefore,
total specific particle energy may be estimated according to
Equation (2)
E.sub.p<E.sub.m+.DELTA.E=E.sub.Tp+V.sub.p.sup.2/2+.DELTA.E
(2)
[0093] Energy loss .DELTA.E may depend on the powder and the
substrate material. Accordingly, energy loss .DELTA.E may be
determined experimentally in each particular case, i.e., for each
given combination of powder and substrate materials.
[0094] The composite powder used in the above-described deposition
technique includes a blend of amorphous or nanocrystalline metallic
particles and nonmetallic particles. Generally, the powder may be
manufactured using different approaches providing different
morphologies for the resulting powders. The following morphologies
of the composite powder are the most effective for the coating
deposition: [0095] 1. Each powder particle is a homogeneous mixture
of amorphous or nanocrystalline metallic particles and nonmetallic
particles or their agglomerates. This type of powder may be
produced, for example, by spray-drying, or other processes
described herein; [0096] 2. The composite powder includes a
metallic component in the form of a continuous matrix of an
amorphous metallic alloy, or an alloy that is capable of existing
in an amorphous state, or constituents of this amorphous metallic
alloy, or any combination of these in which the discrete particles
of nonmetallic component are imbedded in said matrix; [0097] 3. The
composite powder includes discrete particles of nonmetallic
components covered by a film of a metallic component.
[0098] The nonmetallic component of the composite powder includes
discrete particles, discrete agglomerates of particles containing a
metal, or metallic alloy, or any combination thereof. The term
"discrete agglomerates of nonmetallic particles contain a metal or
a metallic alloy" as used herein is intended to refer to a powder
comprising particles having nonmetallic and metallic components,
and is considered to be synonymous with such terms as
"ceramic/metal composite powder" or "cermet." The composite powder
may include a third metallic component.
[0099] The term "amorphous metallic alloy" as used herein is
intended to refer to metals and alloys that are produced, for
example, by rapid solidification process from the liquid state to a
substantially amorphous (noncrystalline) solid state, typically
having less than 50% crystallinity, which is considered to be
synonymous with such terms as "metallic glass" and "glassy metal
alloy" or "nanocrystalline alloy" or "microcrystalline alloy." The
metallic matrix may be made of crystalline materials like Co, Cr,
or Ni alloys, or from amorphous or nanocrystalline metallic alloys.
The content of the metallic component should be not less than 6% by
weight. At lower content of the metallic component it is hard to
expect a continuous metallic matrix in the composite coating, thus
the integrity of the coating could be deteriorated.
[0100] The nonmetallic particles may have a metallic matrix or may
be also embedded into the metallic matrix, which may be understood
as a separate third metallic component blended into the powder. The
composite powder may contain said nonmetallic compound made from at
least one of the compounds selected from the group consisting of
carbides, borides, nitrides, carbonitrides, oxides,
oxycarbonitrides or any combination of these.
[0101] The composite powder is characterized by the discrete
particles of nonmetallic component having a size of less than 50
.mu.m, more preferably less than 25 .mu.m, and most preferably
within the range of 0.2 to 15 .mu.m. The composite powder may have
nonmetallic components in the form of discrete particles, discrete
agglomerates of particles or a combination of these, where the
discrete agglomerates of nonmetallic particles contain a metal or a
metallic alloy in a quantity of 6 to 35% by weight, but no higher
than 94% by weight.
[0102] The novel composite powders envision a great variety of
discrete particles of nonmetallic components which are suitable for
making such a composite powder, including, for example, diamond,
cubic boron nitride, refractory metal carbides (e.g., tungsten
carbides, boron carbide, chromium carbide, silicon carbide),
nitrides (for example, titanium nitride), carbonitrides (e.g.,
titanium carbonitrides, titanium oxycarbonitrides), oxides (e.g.,
silicon oxide, magnesium oxide, aluminum oxide, stabilized
zirconium oxide), pyrolytic carbon, graphite, silica based glasses
and natural or synthetic minerals (e.g., silicates). The powders of
nonmetallic components having discrete particles of any desirable
size are commercially available. The particles selected should, of
course, not react with or dissolve in the metal alloy forming the
amorphous phase.
[0103] It is well known that compounds such as carbon (diamond,
graphite), cubic boron nitride, silicon nitride, oxides and so on,
possess poor wetting with melted metals/alloys and lack the ability
to form strong metallurgical bonds with a metallic matrix. In the
practice of this invention, the surface of the nonmetallic
component particles may be covered with a thin metal film to
promote wetting of nonmetallic particles by a melted metal, and
thus provide first, better and more uniform dispersion of
nonmetallic particles through the melt, and second, better adhesion
of the amorphous metallic component to the surface of the
nonmetallic particles in the composite thermal spray powders.
Nonmetallic components covered (or cladded) with metallic
components may be manufactured by techniques such as physical or
chemical vapor deposition, chemical deposition, electrochemical
deposition and so on. The film thickness depends on a desirable
ratio between metallic and nonmetallic components. Better adhesion
results in higher strength/toughness of the particles, which
prevents disintegration of the composite powder under spraying or
other deposition conditions and thus provides better deposition
efficiency and better characteristics of the coatings.
[0104] The novel composite powders may utilize prior art powders,
such as the amorphous metal-ceramic and microcrystalline
metal-ceramic composites disclosed in U.S. Pat. No. 4,770,701,
which is incorporated by reference. The metal-ceramic composites
are synthesized by solid state reaction-formation methods. These
metal-ceramic composites are characterized by a composition that
ranges from about 75 to about 99.9 percent ceramic in about 0.1 to
about 25 percent amorphous or microcrystalline metal binder
phase.
[0105] The metal components suitable for the novel composite powder
include alloys of Fe, Ni, Co, Cu and combinations thereof, as
described in U.S. Pat. No. 4,770,701. This powder component is
chosen such that once it is deposited upon the ceramic surface and
heat-treatment is initiated, it will readily react with the ceramic
material. Therefore, metal-ceramic component pairings should
reflect a difference in reactivity properties of the two components
sufficient to supply the energy necessary to commence the reaction
and drive it to completion. The metal component, which will be
precipitated onto the ceramic surface, will be about 10 to about
1,000 Angstroms thick. This component can be chosen to compensate
for at least one deficiency of the ceramic material, such as
brittleness and/or formation defects. A metal may be added to
compensate for brittleness by supplying flexibility and ductility
which will allow the composite to absorb expansion and contraction
reactions due to rapid temperature change, or to absorb the shock
when hit solidly by another hard material.
[0106] The composite powders synthesized herein include a thin film
of amorphous or microcrystalline metal material disposed on the
surface region of larger ceramic particles. This thin film acts as
a binder between adjacent ceramic particles. The amount of metal
incorporated into the surface region of the ceramic material in the
form of amorphous or microcrystalline phase matrix binder must be
controlled such that the resultant amorphous or microcrystalline
film is distributed uniformly and evenly around the ceramic
material surface between adjacent ceramic particles. This insures
homogeneity in the resultant composite, and enhances composite
stability with respect to both composition and performance. In U.S.
Pat. No. 4,770,701 the metal may be contacted with the ceramic
material by conventionally known and practiced deposition
techniques, including chemical reaction, electrodeposition,
electroless deposition, and physical deposition techniques.
However, the present teaching eliminates the drawback of the
methods disclosed in U.S. Pat. No. 4,770,701; i.e., the need of at
least two technological steps, wherein the first is related to film
deposition; the second is related to the further heat treatment
providing solid state reaction.
[0107] The present disclosure builds on a number of patents related
to amorphous, nano- and microcrystalline materials. Specifically,
U.S. Pat. No. 3,856,513 is directed to amorphous metallic alloys
having the formula M(a)Y(b)Z(c), where M is at least one metal
selected from the group of Fe, Ni, Co, Cr and V. Y is at least one
element selected from the group consisting of P, B and C. Z is at
least one element selected from the group consisting of Al, Sb, Be,
Ge, In, Sn and Si. In this formula, (a) ranges from about 60 to 90
atom percent, (b) ranges from about 10 to 30 atom percent and (c)
ranges from about 0.1 to 15 atom percent. Furthermore, a variety of
compositions of amorphous metallic alloys were described in, for
example: U.S. Pat. Nos. 4,381,943; 4,692,305; 5,643,531; 4,496,635;
4,410,490; 5,055,144 and 4,834,815, all of which are incorporated
by reference.
[0108] The metallic component of the composite powder may also
utilize various advanced amorphous and nanocrystalline alloys. For
example, the composite powder may utilize the family of amorphous
materials named Armacor.TM., (marketed by Liquidmetals) and
disclosed in U.S. Pat. No. 4,725,512 (which is incorporated by
reference). Alternatively, the composite powder may utilize the
family of amorphous and nanocrystalline Fe-based alloys (Super Hard
Steel--SHS) described in U.S. Pat. Nos. 6,258,185B1 and 6,689,234,
and in US Patent Applications 2005/0013723, 2004/0253381,
2004/0250929, 2004/0120021, 2004/0120017, all of which are
incorporated by reference as if fully reproduced herein. These
types of materials may be used in the preparation of the present
composite powders.
[0109] Some SHS alloys have relatively low thermal conductivity of
about 4-14 W/(m*K). Using this low conductivity, amorphous and
nanocrystalline components may provide additional thermal barrier
benefits to deposited novel composite cermet coatings.
[0110] The deposited metal-ceramic composite coatings and the
coatings including amorphous and nanocrystalline metallic
components provide very good cohesion/adhesion between ceramic
components and amorphous and/or nanocrystalline metallic components
during the deposition process and coating formation.
[0111] The term "amorphous metallic alloy" as used herein is
intended to refer to metals and alloys that are rapidly quenched
from the liquid state to a substantially amorphous (noncrystalline)
solid state, typically having less than 50% crystallinity, which is
considered to be synonymous with such terms as "metallic glass" and
"glassy metal alloy" or "nanocrystalline alloy" or
"microcrystalline alloy." However, the metallic matrix may be made
of crystalline materials like Co, Cr, or Ni alloys, or from
amorphous or nanocrystalline metallic alloys. The content of the
metallic component should be no less than 6% by weight. At lower
content of the metallic component it is hard to expect a continuous
metallic matrix in the composite coating, thus the integrity of the
coating could be deteriorated.
[0112] The amorphous metal alloy also comprises no less than 50% by
volume of the total metallic component of the composite powder. In
another aspect, the composite powder may be characterized by the
fact that the size of the discrete particles or that of the
discrete agglomerates of particles of a metallic component is less
than 100 .mu.m, more preferably less than 45 .mu.m and most
preferably within 15 to 45 .mu.m. The composite coating may also
contain the amorphous metal alloy that includes a crystalline phase
with crystals no larger than 200 nm, or no larger than 100 nm.
[0113] Furthermore, the novel composite powders may include
discrete particles of the nonmetallic component imbedded into the
matrix of the metallic component. The composite coating may also
contain the amorphous metal alloy. Since amorphous metallic alloys
exist in a metastable state, they begin to crystallize, forming a
variety of crystalline phases when heated to a certain and
sufficiently high temperature. This process is called
devitrification. At the intermediate stage in the devitrification
process, the material consists of an amorphous matrix containing a
number of crystalline particles having the size of tens or hundreds
of nanometers. The diffraction pattern thereby begins to change
from that observed for amorphous materials to that observed for
crystalline materials. Amorphous metallic alloys have a substantial
lack of any long-range atomic order and are characterized by X-ray
diffraction patterns consisting of diffuse (broad) intensity
maxima. The crystallized amorphous material could be returned to an
amorphous state by heating to a temperature close to the melting
point. For some of the compositions, crystallized amorphous
materials could regain the amorphous state under mechanical
stresses caused by applying impact, share or compression load.
Examples of these are materials comprising 18-42% by weight of Cr,
1-3.2% by weight of Mn, 3-4.5% by weight of B, 1-3% by weight of
Si, or less than 0.3% by weight of C and Fe, are described in U.S.
Pat. No. 5,643,531, which is incorporated by reference.
[0114] The composite coatings including SHS alloys, as an amorphous
and/or nanocrystalline component, is another example of a possible
phase transformation in novel cermet depositions. SHS forming a
metallic glass during deposition may be devitrified or converted by
heat treatment to a partially crystalline material having a
nanocrystalline grain size and higher hardness in comparison with
the metallic glass. Using these type of alloys as amorphous and
nanocrystalline components of the novel cermet powders and further
heat treatment of deposited coatings, for example by an annealing
or laser beam treatment, may result in a drastic increase of
hardness, wear and erosion resistance of the novel cermet coatings.
Heat treatment may be performed within 600-800.degree. C. for 8-15
minutes, for example, when annealing is applied. The optimum
temperature and time of heat treatment depends on the composition
of a material. For SHS 7170, for example, optimum temperature and
time may be within 680-720.degree. C. and 9-11 minutes
correspondingly.
[0115] The composite powder may have different particle size
distribution, which is dictated by the deposition method used. In
one embodiment, the particle size may be in the range of 40 to 160
.mu.m. In other situations, particle size may be in the range of
20-106 .mu.m, 15 to 53 .mu.m or 15 to 45 .mu.m. Other particle size
ranges may be produced, satisfying requirements for deposition
quality and potential to use a particular deposition process.
[0116] Regarding the powder components, cermets used in the
experiments are manufactured by Praxair Surface Technologies and
their compositions are listed in Table 1 below. SHS 7170 is
manufactured by The NanoSteel Company and in accordance with the
accompanying Material Safety Data Sheet (MSDS) has the following
composition: Iron-balance, 25% or less Chromium; 8% or less
Molybdenum; 10% or less Tungsten, 2% or less Carbon, 5% or less
Manganese; 2% or less Silicon; and 5% or less Boron. Cermet and SHS
7170 powder size was within 15-45 .mu.m.
[0117] The coatings were sprayed with an HVOF torch JP-5000
manufactured by Praxair-Tafa. All experiments were done using a 4''
long barrel, 14'' spray distance and approximately 70 gram/min
powder-feeding rate. The compositions of the spray blended powders,
parameters of spraying, as well as coating properties are presented
in Tables 1 and 2.
[0118] FIGS. 7-10 are optical micrographs of the composite coatings
deposited using a mechanical blend of amorphous alloy powder SHS
7170 with different cermets in accordance with the present
disclosure. All optical micrographs show a cross sectional view of
coatings deposited on a steel substrate. The present micrographs
confirm very good quality of the deposited coating even before
optimization of the component ratios. The coatings are relatively
dense exhibiting substantially no cracks or other defects, and
exhibiting a perfect interface between the particles.
[0119] Referring to FIG. 11, the coating microstructure shows
extremely good bonding between metallic and cermet particles. FIG.
11 shows an indentation area made during a Vickers microhardness
(DPH 300) measurement. This indentation did not cause any cracks or
defects due to symmetrical indentation and thus confirms the high
quality of the coating, which is dense, shows a high quality
interface between particles, and great cohesion.
[0120] The data related to the coating properties shows that even
50% SHS 7170 still allows getting a very dense coating with
extremely good micro- and superficial hardness, which may
demonstrate good wear and erosion resistance. At the same time high
amounts of SHS 7170 binder may result in a significant increase in
corrosion and oxidation resistance.
[0121] In general, increases in the amount of SHS 7170 decrease the
micro-hardness and the superficial hardness and increase the
coating toughness. The component ratio is selected prior to coating
deposition to create a coating with selected properties, as shown
in FIG. 2.
[0122] FIGS. 13A-14B are optical micrographs of different composite
coatings oxidized in air for 5 hours at 750.degree. C. and
850.degree. C. All micrographs show high quality coatings. High
oxidation resistance was confirmed by oxidation tests in air
performed for 5 hours at 750.degree. C. and 850.degree. C. Coatings
#1 and #3-1 were tested simultaneously with coating W-balance; Cr
4%; Co 10%; C 5.3% commercially available and manufactured, for
example, by Praxair.
[0123] FIGS. 13A, 13B, and 13C illustrate the microstructure of the
coatings after oxidation in air at 750.degree. C. and FIGS. 14A and
14B illustrate the microstructure of the coatings after oxidation
in air at 850.degree. C. The addition of the amorphous alloy
component significantly increased the oxidation resistance of the
carbide-based coatings consisting of W-balance; Cr 4%; Co 10%; C
5.3%. This is evident when comparing FIGS. 13A and B with FIG. 13C
exhibiting internal oxidation (dark oxidation region O) inside the
deposited coating (shown in cross section in FIG. 13C).
[0124] FIGS. 14A shows the microstructure of a good coating
(including 50% SHS) after oxidation in air at 850.degree. C., where
there are no significant oxidation regions associated with the
coating. FIG. 14B shows the microstructure of a coating) having no
SHS (i.e. without amorphous alloy) after oxidation in air at
850.degree. C., where the coating was completely oxidized and
degraded. The oxidized coating having no SHS 7170 (FIG. 14A) is in
direct contrast with the high quality coating having 50% of SHS
7170 (FIG. 14B) that is shown practically intact.
[0125] Additional composite coatings were deposited as follows:
Composite powder was made by blending powders based on 1350 VM
powder manufactured by Praxair and SHS 7170 and SHS 7574
amorphous/nanocrystalline alloys manufactured by NanoSteel, Inc.
SHS 7170 was used in the experiments once again to check the
repeatability of coating performance. SHS 7170 and SHS 7574 powders
were reclassified avoiding potential build up (barrel loading) of
the JP 5000 barrel. Powder blend #18 was prepared using 35% of
alloy SHS 7574 screened through a 500 mesh sieve and a 635 mesh
sieve to attain particles of a size between 20 to 25 .mu.m. This
blend was tested with all other blends to determine the influence
of the alloy particle size on a coating and its performance.
Compositions of sprayed powders and related calculated densities
are shown in Table 3.
[0126] The specimen was prepared as follows: All 1/4'' and 1/8''
thick coupons went through 2 steps of surface preparation. The
first step was a manual grit blasting by aluminum oxide (alumina)
grit #46/70 at a pressure of 80 psi and a distance of 4 inches. The
second step was an additional grit blasting by alumina grit #24 at
80 psi of pressure and a distance of 4 inches. Two carbon steel
3''.times.1''.times.1/8'' coupons for metallography and related
studies and one carbon steel 3''.times.1''.times.1/4'' coupon for
the G-65 abrasion resistance test were sprayed per set of
parameters. SS410 specimens were used for the bond strength
tests.
[0127] A high-velocity oxygen-fuel thermal spray system (HVOF)
JP-5000 manufactured by Praxair-Tafa was used for the described
experiments. The following spraying parameters optimized for 1350VM
powder were kept constant during the experiments: [0128] Oxygen
flow rate: 2000 cubic feet per hour (scfh); [0129] Kerosene flow
rate: 5.8 gal/h;
[0130] The oxygen and kerosene flow rates provided approximately
100 psi combustion pressure and a 1.25 stoichiometry ratio.
[0131] The following spraying distance, motion-related and cooling
conditions were also kept constant during the experiments: [0132]
Spraying distance: 14 inches; [0133] Traverse horizontal speed:
24''/sec; [0134] Vertical increment: 5 mm; [0135] Cooling
conditions: 4 air jets around the barrel were used for substrate
cooling. Jet size ID=1/4''; [0136] Air pressure: approximately 80
psi. [0137] Spraying surface temperature was measured by infrared
thermometer during spraying and did not exceed 270.degree. F.
[0138] The carrier gas flow rate was adjusted during experiments,
keeping a symmetrical spray pattern. Powder feed rate was within
65-74 g/min and the total number of passes was adjusted for each
type of powder providing a total coating thickness of approximately
27-34 thousands of an inch (34 mils). In this deposition, no
attempt was made to optimize spraying parameters for the novel
composite powders.
[0139] The sprayability data are summarized in Table 4. The
sprayability study showed that NanoCermet materials can provide a
12-72% higher deposition rate per mil of a coating, resulting in a
savings in powder costs of about 15-43% due to the 40-70% lower
cost of the amorphous/nanocrystalline alloys in comparison with the
cost of the 1350VM powder. Thus, cost of applications can be
significantly decreased, thereby improving the economics of the
existing WC-based coatings. This is presently particularly
important due to the continuously increasing prices of W, Co, Cr
and other materials.
[0140] Several composite coatings were deposited using the
above-described technique. Furthermore, a control coating, made of
only the 1350VM powder, was deposited for comparison. FIG. 15A
shows microstructures of the coating made with the composite powder
made of 65% of 1350VM and 35% of SHS 7574 having particle size of
20-25 .mu.m. FIG. 15B shows microstructures of the coating made
with the composite powder made of 65% 1350VM and 35% SHS 7574
having a particle size of 20-45 .mu.m. FIG. 15B shows
microstructures of the coating made with the composite powder made
of 65% 1350VM and 35% SHS 7574 having a particle size of 20-45
.mu.m. FIG. 16 shows microstructures of the coating made with the
composite powder made of 50% 1350VM and 50% SHS 7170 sprayed using
separate powders fed using two injectors. FIG. 18 shows
microstructures of the coating made with the composite powder made
of 80% WC and 20% SHS 7170. FIG. 17A shows the coating made with a
composite powder made of 65% 1350 VM and 35% SHS 7170 after the
microhardness measurement. FIG. 17B shows the coating made with
only SHS 7170 after the microhardness measurement.
[0141] The tests of the deposited coatings are summarized in Table
5, where several conclusions can be drawn from the observations and
data. The optical micrographs of a 1350VM coating show it being
homogeneous without visible structural defects and cracks. The
porosity is below 1%, with the oxide content below the limit of
determination by the standard optical microscopy test. However, the
1350VM coating exhibits vertical and horizontal cracks. The
presence of these cracks may be due to a 1350VM coating being near
its performance limits at a thickness of 27 mils and thus not
having enough toughness to withstand stresses.
[0142] On the other hand, all seven deposited composite coatings
are homogeneous without visible structural defects and cracks. The
porosity is below 1%, with the oxide content below the limit of
determination by the standard optical microscopy test. In the
optical micrographs, there were no micro defects detected between
1350VM and both amorphous/nanocrystalline alloys' splat boundaries,
which mark the borders between the materials deposited by each
droplet. This lack of defects importantly confirms that the
amorphous alloys have good affinity for the nonmetallic
constituents of the coatings.
[0143] The micro-hardness measurements were done by performing
typical Vickers indentations into the composite coatings at a 300
gram load (as previously illustrated in FIG. 11), and at a 1,000
gram load as illustrated in FIGS. 17A and 17B. The coatings sprayed
using only using amorphous/nanocrystalline alloys SHS 7170 and SHS
7574 do not have visible structural defects and cracks. However,
these coatings exhibited excessive brittleness and some
inter-particle defects after the Vickers indentations, as
illustrated in FIG. 17B. Importantly, the novel composite coatings
did not show any defects between metallic and carbide particles
related to the Vickers indentations, which again confirms that the
amorphous alloys have a good affinity for the nonmetallic
constituents of the deposited coatings.
[0144] The best surface roughness was detected for coating 18, as
shown in Table 5, which is explainable by the finer size of the
completely melted particles of the alloy SHS 7574. This makes for
very thin and evenly distributed lamellas of SHS 7574 and related
dense packaging of the composite material in the coating.
[0145] The microhardness of the sprayed 1350VM reference coating
was 1340 DPH300, which is higher by 90 kg/mm.sup.2 than was
obtained during the first set of experiments presented in Table 1.
This difference is due to the correction/optimization of the
spraying parameters, and thus illustrates the effect of
optimization of the spraying parameters. As seen in Table 5, the
microhardness of the coatings sprayed with 1350VM--nanocermet
blends is less than that for pure 1350VM. The observed drops in DPH
of the composite coatings were expected, and are related to the
increased total content of the metallic constituents of the
composite powders and coatings. The microhardness of nanocermet
composite coatings can be improved by the optimization of spraying
parameters. (As was mentioned above, the spray parameters in this
experiment were solely optimized for 1350VM composition).
[0146] Referring still to Table 5, the superficial hardness 15N of
1350VM is about 91, while superficial hardness of nanocermet
compositions is about 90-92 depending on the content of the alloy
component. The bond strength of 1350VM coatings was about 12,300
psi, while all the composite coatings exhibited bond strengths
above 13,500 psi. This is because of glue bond failure under such a
big load. The higher bond strength for the composite coatings was
expected, as described earlier, considering the unique bond
strength of the amorphous coatings.
[0147] Table 6 also displays the results of the G-65 tests. The
standard test method for measuring abrasion using the Dry
Sand/Rubber Wheel Apparatus was done in accordance with the ASTM
G-65 protocols. It is clear that the composite coatings containing
85% 1350VM by weight and 15% amorphous/nanocrystalline components
by weight performed as well as the 100% 1350VM coating. These
composite coatings can be further improved by optimizing the
spraying processes and related parameters for the powder
composition and the particle size.
[0148] Alloys SHS 7170 and 7574 have relatively low thermal
conductivity, as mentioned above. The thermal conductivition can
also be evaluated by examining the appearance of the back of the
carbon steel coupons, which were 1/8'' thick. The coupon sprayed
solely with 1350VM exhibited a dark grey color caused by oxidation
as a result of the relatively high temperature of the back of the
coupon. The high temperature is due to the high thermal
conductivity of the 1350VM coating. On the other hand, the back of
the coupon sprayed with the amorphous/nanocrystalline alloy SHS
7170 exhibited no significant changes in color. This shows that the
temperature of the coupon was lower due to the low thermal
conductivity of the SHS 7170 alloy. The back of the coupon sprayed
with the blend consisting of 50% 1350VM by weight and 50% SHS 7170
by weight shows very minor changes in color. This shows that the
composite coatings made from 50% 1350VM and 50% SHS 7170 may have a
relatively low thermal conductivity and may simultaneously perform
wear, erosion and thermal barrier protection of the sprayed
substrates. This is very useful in many applications where the
coatings are deposited prior to use or on surfaces of refurbished
parts.
[0149] Table 7 illustrates the results of the erosion tests in
terms of weight loss and volume loss. The erosion tests were done
using alumina grit no. 46-70 using a standard setup having a
blasting nozzle located at a selected distance from the examined
surface. The grit blasting nozzle accelerated the grit at an air
blasting pressure of about 80 psi. The nozzle was located 90
degrees relative to the blasted surface of the coating sprayed on
the 1/8'' thick coupon. The distance between the nozzle exit and
the blasted surface was 2 inches. Two hundred and twenty-five grams
of grit were used to test each coating. The weight of the samples
before and after grit blasting was measured to determine weight
loss. Volume loss was calculated as weight loss divided by the
coating density. The summary of the erosion data is in Table 7. The
data shows that the novel composite coatings having 15% by weight
of alloys SHS 7170 or SHS 7574, as well those having 35% by weight
of SHS 7170 outperformed the benchmark coating 1350VM. Other
composite coatings showed erosion resistance similar to the 1350VM
coating. The erosion resistance of coatings made up of only SHS
7170 or SHS 7574 was determined to be approximately 1.4-2 times
worse in comparison with erosion resistance of the novel composite
coatings.
[0150] The compressive stress estimates were done using carbon
steel samples having dimensions 3''.times.0.75''.times.0.031''
(Almen standard stripes, type N). The samples were flattened after
a grit blasting. The deflection of the samples was measured after
spraying. A summary of the deflection tests is shown in Table 8.
The results show that stress may be controlled by a ratio of
nonmetallic components to the amorphous/nanocrystalline metallic
component. For example, the 1350VM coating, as well as the novel
composite coatings having 15 and 35% by weight of alloys SHS 7170
or SHS 7574, exhibited compressive stress. Increasing the content
of the SHS alloy up to 50% resulted in practically neutral stress.
It may be expected that further increasing of the content of an
amorphous/nanocrystalline metallic component would result in
tensile stress, as coatings sprayed by only SHS 7170 or SHS 7574
demonstrated tensile stress.
[0151] The stress of the composite coatings may also be controlled
by the size of the amorphous/nanocrystalline metallic particles.
FIG. 15A shows microstructures of the coating made with the
composite powder (65% 1350VM and 35% SHS 7574) having a particle
size of 20-25 .mu.m. At the deposition point, these smaller
particles were substantially melted and extended in the horizontal
direction (i.e., in the spray direction and perpendicular to the
spray increment). FIG. 15B shows microstructures of the coating
made with the composite powder (65% 1350VM and 35% SHS 7574) having
a particle size of 20-45 .mu.m. At the deposition point, the larger
particles were not melted. Thus, the changes in the size of the
amorphous/nanocrystalline alloy SHS 7574 from about 20-45 .mu.m to
about 20-25 .mu.m resulted in changes in stress from compressive to
neutral in the sprayed coatings. Having all SHS 7574 particles
melted may explain the difference in performance. The coating shown
in FIG. 15A is expected to exhibit great anticorrosion properties,
but somewhat smaller wear resistance compared to the coating shown
in FIG. 15B, which is expected to exhibit a high wear
resistance.
[0152] There are additional examples of the composite powder
designed for deposition of coatings having desired properties.
EXAMPLE 2
[0153] To make the composite powder designated CP-2, commercially
available powders 1350VM from Praxair Surface Technologies and SHS
7170 powder manufactured by Nanosteel, Inc. are used.
[0154] Composite powder CP-2 is made as follows: the thermal spray
powder having a nominal composition of 86% by weight tungsten
carbide (WC), 10% by weight Cobalt (Co) and 4% by weight Chromium
(Cr), or 1350VM powder, is screened through a 325 mesh sieve to
insure the absence of coarse particles larger than 45-50 .mu.m.
Similarly, the amorphous metallic alloy powder, grade SHS 7170,
manufactured by Nanosteel, Inc. is also screened through a 325 mesh
sieve for the same purpose. SHS 7170 is composed of 25% or less
Chromium, 8% or less Molybdenum, 10% or less Tungsten, 2% or less
Carbon, 5% or less Manganese, 2% or less Silicon, 5% or less Boron,
and a balance of Iron. Additionally, these powders are screened
through a 635 mesh sieve to remove fine particles having a size of
less than 15 .mu.m. After screening, 8.50 lbs of 1350VM powder and
1.50 lbs of SHS 7170 powder are loaded in a V-type blender having a
capacity of about 1 cubic foot, and are blended for 30 min at 30
rpm.
EXAMPLE 3-7
[0155] Composite powders having various amounts of each component,
designated as Composites No. 3 through No. 7 are prepared as
described in the protocol for composite powder CP-2, above.
However, powder SHS 7170 may be replaced with component SHS 7574
(also manufactured by Nanosteel, Inc.), and different quantities of
each component are used for each of the different composite
powders. Metallic alloy powder SHS 7574 has a composition similar
to SHS 7170, but includes a higher content of Molybdenum.
TABLE-US-00001 Quantity Components loaded in V-blender Composite
1350Vm SHS 7170 SHS 7574 Powder (lbs.) (lbs.) (lbs.) CP-2 8.50 15.0
0.00 CP-3 8.50 0.00 1.50 CP-4 6.50 0.00 3.50 CP-5 6.50 3.50 0.00
CP-6 5.00 5.00 0.00 CP-7 5.00 0.00 5.00
EXAMPLE 8
[0156] To make the composite powder designated CP-8, commercially
available powders 1350VM from Praxair Surface Technologies and SHS
7574 powder manufactured by Nanosteel, Inc. are used.
[0157] CP-8 is made as follows: Powder 1350VM is screened through a
325 mesh sieve to insure the absence of coarse particles larger
than 45-50 .mu.m. Metallic alloy powder SHS 7574 is then screened
through a 500 mesh sieve and the resulting powder which passed the
500 mesh sieve is additionally screened through a 635 mesh sieve to
obtain particles having a size of about 30 to 20 .mu.m. After
screening, 8.50 lbs of 1350VM powder and 1.50 lbs of SHS 7574
powder are loaded in a V-type blender having a capacity of about 1
cubic foot, and are blended for 30 min at 30 rpm.
EXAMPLE 9
[0158] Commercially available powder of the amorphous alloy, grade
SHS 7170, (Nanosteel, Inc.) is screened through a 500 mesh sieve to
obtain a fine powder having a particle size of less than 30 .mu.m.
This fine SHS 7170 powder is then comminuted by jet milling with a
Hosokawa Micron Ltd. jet mill to provide a feedstock powder of the
amorphous alloy with a mean particle size of about 2.5 .mu.m as
measured by Microtrac, and a Fisher Subsieve Size number (FSSS) of
about 1.5 as measured by the Fisher Subsieve Sizer. The high
oxidation resistance of the alloy is tested by analyzing the
jet-milled powder's oxygen content. No significant increase in
oxygen content should be found.
[0159] Twenty pounds of WC powder having an FSSS number of 1.6
(manufactured by Buffalo Tungsten, Inc.), 5.0 lbs of jet-milled SHS
7170 powder, 1.2 gal of water, 0.075 lbs of Darvan-C dispersant and
0.125 lbs of Optapix polyvinylacetate binder are loaded into
vibratory mill model DM-1 (Sweco) containing 100 lbs of 1/4'' size
grinding balls made of WC-6Co cermet. The dispersant and the binder
correspond to 0.3% by weight and 0.5% by weight of the total
solids, respectively. The components are vibro-milled for 4 hrs,
and the resultant slurry is transferred to a tank equipped with an
impeller stirrer. Particle size of the slurry is tested by
Microtrac. All particles must have a particle size of less than 11
.mu.m, and 85% of these must have a particle size of less than 5.5
.mu.m.
[0160] The prepared slurry is then spray-dried using a Niro pilot
rotary atomizer at a feed rate of 0.04 gal/min, an outlet
temperature of 110.degree. C., and 5000 rpm of the atomizer head. A
collected 22 lbs of spray-dried powder is screened through a 230
mesh sieve to remove excessively coarse particles. It is then
screened through a 500 mesh sieve to remove excessively fine
particles and dust. A resulting 12 lbs of the cleaned spray-dried
powder is placed into graphite boats as 1'' thick flat layers. The
boats are covered with graphite lids, loaded into a Centorr vacuum
furnace and sintered for 2 hrs at 1200+/-20.degree. C. while
surrounded by Ar gas at a pressure of 600 mTorr. The porous
briquettes of sintered powder are deagglomerated by screening
through an 80 mesh sieve first and then screening through 170 and
270 mesh sieves. Finally, the resulting powder is blended in a
V-type blender for 2 hrs at 30 rpm.
[0161] The deagglomerated powder is screened through a 325 mesh
sieve and then through a 635 mesh sieve. The protocol yields 9.5
lbs of the novel composite powder having about 15% by weight of the
amorphous metallic binder. The morphology of the powder particles
is typical for the spray-drying and sintering process. The
particles are spheroidal low porous particles with distinguishable
grains of tungsten carbide which are covered/conjoined with a
layer/film of metallic component.
[0162] Example 10 provides a protocol illustrating the preparation
of spray-dried but not sintered powders of the novel composite.
[0163] First, the amorphous alloy powder, SHS 7170 (Nanosteel,
Inc.) is screened through a 500 mesh sieve to obtain fine alloy
powder having a particle size of less than 30 .mu.m. This fine SHS
7170 powder is then comminuted by a jet milling technique with a
Hosokawa jet mill to provide a feed stock powder of the amorphous
alloy with a mean particle size of about 2.5 .mu.m as measured by
Microtrac and an FSSS of about 1.5, as measured by the Fisher
Subsieve Sizer. The high oxidation resistance of the alloy is
tested by analyzing the jet-milled powder's oxygen content. No
significant increase in oxygen content should be found.
[0164] Twenty pounds of WC powder having an FSSS number of 1.6
(manufactured by Buffalo Tungsten, Inc.), 5.0 lbs of the jet-milled
SHS 7170 powder, 1.2 gal of water, 0.075 lbs of Darvan-C dispersant
and 0.50 lbs of Optapix polyvinylacetate binder are loaded into
vibratory mill model DM-1 (Sweco) containing 100 lbs of 1/4'' size
grinding balls made of WC-6C0 cermet (commercially available) for
milling. The dispersant and the binder correspond to 0.3% by weight
and 2.0% by weight of the total solids, respectively. The
components are vibro-milled for 4 hrs, and the resultant slurry is
transferred to a tank equipped with an impeller stirrer. The
particle size of the slurry is tested by Microtrac. All particles
must have a particle size of less than 11 .mu.m, and 85% of these
must have a particle size of less than 5.5 .mu.m.
[0165] The prepared slurry is then spray-dried using a Niro pilot
rotary atomizer at a feed rate of 0.04 gal/min, an outlet
temperature of 110.degree. C., and 5000 rpm of the atomizer head.
Because a spray-dried powder contains both very coarse and very
small particles, these should be removed. When this is done, the
yield decreases and the fraction of the resulting spray-dried
powder, after going through the 325-500 mesh, is approximately 11
lbs. This powder is further screened through a 325 mesh sieve to
remove excessively coarse particles. It is then screened through a
500 mesh sieve to remove excessively fine particles and dust.
[0166] A resulting 11 lbs of the cleaned spray-dried powder is
placed into stainless steel boats as 1/2'' thick flat layers. The
boats are heated in an oven for 2 hrs at 150+/-5.degree. C. to make
the organic binder insoluble in water. The morphology of the
resulting powder's particles is typical for the spray-drying
process. The resulting powder includes spheroidal porous particles
with distinguishable grains of tungsten carbide conjoined with
finely dispersed metallic particles
[0167] Example 11 provides a protocol illustrating the preparation
of sintered and crushed powders of the novel composite. First, the
amorphous alloy powder, SHS 7170 (Nanosteel, Inc.) is screened
through a 500 mesh sieve to obtain fine powder of the alloy having
a particle size of less than 30 .mu.m. This fine SHS 7170 powder is
then comminuted by a jet milling technique with a Hosokawa jet mill
to provide a feed stock powder of the amorphous alloy with a mean
particle size of about 2.5 .mu.m as measured by Microtrac and an
FSSS of about 1.5, as measured by the Fisher Subsieve Sizer. The
high oxidation resistance of the alloy is tested by analyzing the
jet-milled powder's oxygen content. No significant increase in
oxygen content should be found.
[0168] Sixteen pounds of WC powder having an FSSS number of 1.6
(manufactured by Buffalo Tungsten, Inc.) and 4.0 lbs of jet-milled
SHS 7170 powder are loaded into a V-type blender having a capacity
of about 1 cubic foot and blended for 2 hrs at 20 rpm. The blend of
components is placed into a graphite boat and hand compacted by
tapping the powder with 4''.times.4''.times.8'' stainless steel
plates. The boat is covered with a graphite lid, loaded into a
Centorr vacuum furnace and sintered for 1 hr at 1250+/-20 .degree.
C. while surrounded by Ar gas at a pressure of 600 mTorr.
[0169] The solid briquette of sintered powder is crushed into
fragments of less than about 1/8'' in size with a jaw-crusher, and
then crushed further with a roll-crusher. The crushed powder is
passed through an impact mill, thus reducing the size of the
particles down to 65 .mu.m or less. This powder is screened through
a 325 mesh sieve and any oversized powder particles are passed
through the impact mill once more for a total of 3 to 5 passes
through the impact mill. The yield is about 18.5 lbs of powder.
[0170] The resulting powder is screened through a 325 mesh sieve
and then through a 635 mesh sieve. The yield after this step is
16.1 lbs of the novel composite powder having about 15% by weight
of the amorphous metallic binder. The morphology of the particles
of the powder is typical for the sintering and crushing process.
These are shapeless particles, looking like pieces of broken glass,
having no distinguishable substructure.
[0171] The surfaces of the substrates are usually cleaned by grit
blasting and degassing. Initially, degreasing is needed to remove
any oil, grease or other organic residues from the surface. Acetone
is used to clean the surface of the coupons as the first step of
surface preparation. Hot vapor degreasing, ultrasonic cleaning and
other methods may be used as well if a surface has significant
contamination. Grit blasting is used to clean the surface to remove
possible oxide scales, oxide films, etc., as well as to activate
the surface. Grit blasting creates a predetermined surface
roughness depending mainly on grit size, blasting pressure,
blasting angle and distance from the surface. The surface roughness
of 25-50 micrometers is commonly recommended as a starting point
for the process of High Velocity Oxygen Fuel thermal spraying
(HVOF) and some other coating deposition methods. This surface
roughness for HVOF depositions on thin coupons used for
deflection/stresses estimates is achieved by grit blasting using
alumina grit #46-70 at a pressure of 80 psi and a distance of 4''
from the coupon surface.
[0172] The surface roughness of approximately 60-125 .mu.m is
required for plasma depositions as well as for some HVOF heavy-duty
applications. Surface roughness of about 70-80 .mu.m is achieved on
3''.times.1''.times.1/8'' and 3''.times.1''.times.1/4'' coupons by
grit blasting using alumina grit #24 at a pressure of 80 psi and a
distance of 4'' from the coupon surface.
[0173] The deposition system and parameters are optimized depending
on the composition of the above-described composite powder, and the
particle size. The liquid fuel-based HVOF systems enable efficient,
inexpensive deposition the novel composite coating. The JP-5000
thermal spray system (manufactured by Praxair Tafa, Inc.) may be
used to spray coatings. When using JP-500, each blend is loaded
into a powder feeder connected through a powder hose and a splitter
with 2 powder injectors located on a barrel. The following spraying
JP-5000 parameters used for the deposition of powder blends: [0174]
Oxygen flow rate: 2000 scfh; [0175] Kerosene flow rate: 5.8 gal/h;
[0176] Powder feed rate: approximately 70 grams/min.
[0177] The oxygen and kerosene flow rates stated above provide a
pressure of approximately 100 psi combustion and a stoichiometry
ratio of approximately 1.25.
[0178] The JP-5000 thermal spray system may use the following
spraying and motion parameters for depositions of the composite
coatings: [0179] Spraying distance: 14 inches;--Traverse horizontal
speed: 247 sec; [0180] Vertical increment: 5 mm; [0181] Substrate
cooling is done with 4 air jets around the barrel. (Jets I
D=1/4''); [0182] Air pressure: approximately 80 psi.
[0183] The conditions stated above provide a spraying surface
temperature below 270.degree. F. and a coating deposition rate of
approximately 25-40 .mu.m per pass over coupon. The temperature of
the spraying surfaces is measured with an infrared thermometer
during spraying and should not exceed 270.degree. F.
[0184] According to another example, the JP-5000 thermal spray
system may be used to spray novel composite coatings using 2 powder
feeders so that the nonmetallic components and
amorphous/nanocrystalline metallic components are fed into the
system separately. The powder feeder is loaded with 1350VM powder,
is calibrated at approximately 35 grams/min feed rate and connected
with the first powder injector. The second powder feeder is loaded
with amorphous/nanocrystalline alloy SHS 7170 powder, is calibrated
at approximately 35 grams/min feed rate and connected with the
second powder injector. A composition consisting of 50% 1350VM by
weight and 50% SHS 7170 by weight may be sprayed using this
approach. (FIG. 16 illustrates a composition consisting of 50%
1350VM by weight and 50% SHS 7170 by weight.) When each powder
feeder is calibrated for the rate of 35 grams/min, then
approximately 50-50 deposition is sprayed.
[0185] According to another example, the composite coating is
formed from an unmelted nonmetallic component and an
amorphous/nanocrystalline metallic component under different
conditions. The above provided parameters for the JP-5000 thermal
spray system (i.e., oxygen flow rate of 2000 scfh; kerosene flow
rate of 5.8 gal/h and powder feed rate of approximately 70
grams/min) heat the 20-53 .mu.m particles of tungsten carbide below
about 2000.degree. C., which is significantly less than tungsten
carbide's melting point of about 2700.degree. C. Under the same
conditions, the SHS 7574 particles would be heated up to a
temperature of approximately 1400-1800.degree. C. if their size is
about 20-25 .mu.m. This is significantly above the melting points
of SHS alloys, which are about 1100-1300.degree. C. Under these
conditions, the SHS 7574 particles of approximately 35-45 .mu.m
would be heated up to 900-1100.degree. C. Therefore, these
relatively big particles are largely unmelted.
[0186] Two blends consisting of 35% SHS 7574 by weight and 65%
1350VM by weight are used for coatings, with a first having a
particle size of 20-25 .mu.m (using -500+635 mesh sieve) and a
second having a particle size of 20-45 .mu.m (-325+635 mesh size).
The micrograph of the cross section of the deposit made up of the
first blend (FIG. 15A) demonstrates that all SHS 7574 particles
were melted and formed fine thin lamellas in the deposition. The
micrograph of the cross section of the deposit made up of the
second blend (FIG. 15B) demonstrates that some of the SHS 7574
particles were melted (the fine particles) and formed fine thin
lamellas in the deposition. The image also shows that another
portion of the SHS 7574 particles were not melted (the larger
particles), and formed relatively rounded particles or thick
lamellas within the coating. No cracks or similar defects were
observed in the unmelted SHS 7574 particles, which may be
considered proof that their temperature was above the temperature
of brittle-ductile transition.
[0187] According to another embodiment, the composite coatings may
also be sprayed with a Jet Kote HVOF system manufactured by Deloro
Stellite Coatings, Inc. The composite coatings may be sprayed using
the Jet Kote system at a hydrogen flow rate of approximately
1100-1400 scfh and an oxygen flow rate of approximately 450-600
scfh. Fuel rich combustion mixtures are recommended as a rule by
Stellite so that the combustion mixture is less likely to oxidize
particles.
[0188] According to another embodiment, the composite coatings may
also be sprayed with the Diamond Jet DJ 2600 HVOF system
manufactured by Sulzer Metco Ltd. The composite coatings can be
sprayed using the DJ 2600 system at flow rates similar to those
described for the Jet Kote system (a hydrogen flow rate of
approximately 1100-1400 scfh and an oxygen flow rate of
approximately 450-600 scfh). Diamond Jet also needs an additional
700-1000 scfh of cold air or nitrogen which is fed into the
convergent part of the nozzle for cooling.
[0189] According to another embodiment, the following examples are
given to illustrate the process of heat treatment of the novel
composite coatings. The composite coatings containing 15% SHS 7170
by weight and 85% 1350VM by weight were sprayed on
3.times.1.times.1/2'' steel coupons using the following spraying
JP-5000 parameters: [0190] Oxygen flow rate: 2000 scfh; [0191]
Kerosene flow rate: 5.8 gal/h; [0192] Powder feed rate:
approximately 70 grams/min. [0193] Spraying distance: 14
inches;--Traverse horizontal speed: 247 sec; [0194] Vertical
increment: 5 mm; [0195] Substrate cooling is done with 4 air jets
around the barrel. (Jet ID=W); [0196] Air pressure: approximately
80 psi.
[0197] Then, the substrates with the resulting composite coatings
are loaded into a vacuum furnace and gradually heated up to 700
(+/-5).degree. C., increasing the temperature at a rate of
4.5.degree. C./min, while surrounded by Ar gas at a back pressure
of 600 mTorr. At 700.degree. C. the samples are incubated for 30
min. The furnace is then turned off and allowed to cool down to
room temperature. The temperature of the heat treatment is about
60.degree. C. above the devitrification temperature of SHS
7170.
[0198] According to yet another embodiment, the composite coatings
containing 15% SHS 7574 by weight and 85% 1350VM by weight are
sprayed on 3.times.1.times.1/2'' steel coupons using the parameters
described above. The substrates with the resulting composite
coatings are loaded into a vacuum furnace and heated up to 750
(+/-5).degree. C., increasing the temperature at a rate of
4.5.degree. C./min, while surrounded by Ar gas at a back pressure
of 600 mTorr. At 750.degree. C. the samples are incubated for about
30 min. The furnace is then turned off and allowed to cool down to
room temperature. The temperature of the heat treatment is about
50.degree. C. above the devitrification temperature of SHS
7574.
[0199] Additional embodiments are combinations of the
above-described composite powders (their compositions and particle
sizes), and deposition parameters including the oxygen flow rate,
the fuel flow rate, the powder feed rate, the spraying distance,
the traverse horizontal speed, the vertical increment, the
substrate cooling and other parameters.
* * * * *