Process for applying a functional gradient material coating to a component for improved performance

A method for applying a functionally gradient coating on a component, having a surface and subjected to one or more of rolling, sliding, abrasion and bending contacts, including the step of thermally spraying a functionally gradient material (FGM) on said surface that forms an FGM coating, said FGM coating having a thickness, a plurality of material compositions and a plurality of elastic modulus profiles. Each elastic modulus profile consists of a plurality of elastic modulii at a plurality of corresponding points within that thickness. The elastic modulii are in the range from about 28 Mpsi to about 60 Mpsi. Optionally, there is also a plurality of carbon content profiles.

TECHNICAL FIELD 
The present invention relates generally to the application of functionally 
gradient materials (FGMs) in the design of various components and more 
particularly, to use of FGM coatings on machine components subjected to 
one or more of rolling, sliding, abrasion, and bending contacts in order 
to increase their performance characteristics. 
BACKGROUND ART 
Gears, bearings, camshafts, planet shafts, and other engine, transmission, 
and/or undercarriage components in a machine, such as an earthworking 
machine, are constantly subjected to rolling and/or sliding contacts. 
Track links, track rollers, bushings, idlers and ground engaging tools 
(GETs) are generally also subjected to abrasive wear and/or bending 
forces. In order to increase the durability and reliability of the 
components that experience such contacts, these metallic components are 
usually case hardened. Case hardening results in the component having a 
harder outer surface and a relatively softer inner core and is 
accomplished by methods such as carburizing, induction hardening, flame 
hardening, or other selective hardening processes known to those skilled 
in the art of heat treatment. 
One disadvantage of case hardening by these case hardening processes is 
that hardness gradients are introduced through a differential gradient of 
martensitic and non-martensitic structures that is independent of the 
elastic modulus of the component. Thus, even though the outer surface of 
the component may have a greater hardness than the inner core and 
consequently have better wear resistance, if the loads or stresses are 
kept constant, the deflection or strains of the component is unchanged. In 
other words, the component still undergoes a constant amount of deflection 
at a constant load. This inability to tailor a component's deflection at 
greater loads has long been a bottleneck in the design of various types of 
components that are subjected to a variety of contacts enumerated above. 
It has been desirable to have components subjected to rolling and/or 
sliding load conditions that are designed to exhibit varying amounts of 
Von Mises stresses in response to a constant amount of deflection. In 
other words, it has been desirable to have components which are tailored 
to exhibit varying amounts of deflection at a fixed amount of load, thus 
tailoring the bending or contact fatigue resistance or wear resistance of 
the component according to its intended application in a machine. It has 
thus been desirable to have components having an elastic modulus profile 
in relationship to the depth from the surface of the component, and also 
in relationship to the geometrical configuration of the component, so as 
to obtain components that exhibit a desired amount of fatigue or wear 
resistance enhancement when subjected to one or more of rolling, sliding, 
abrasion or bending contacts. 
The present invention is directed to overcome one or more problems of 
heretofore utilized components that are subjected to one or more of 
rolling, sliding, abrasion, or bending contacts. 
DISCLOSURE OF THE INVENTION 
An aspect of the present invention, a process for applying a functionally 
gradient coating on a component, having a surface and is subjected to one 
or more of rolling, sliding, abrasion or bending contacts, including the 
step of thermally spraying a functionally gradient material (FGM) on said 
surface that forms an FGM coating, said FGM coating having a thickness, a 
plurality of material compositions and a plurality of elastic modulus 
profiles. Each elastic modulus profile consists of a plurality of elastic 
modulii at a plurality of corresponding points within that thickness. The 
elastic modulii are in the range from about 28 Mpsi to about 60 Mpsi. 
Optionally, there is also a plurality of carbon content profiles. 
The component comprises a surface that FGM coating has a thickness. The FGM 
coating has a plurality of material compositions. The material selected 
for these applications are alloy steels. The FGM composition is adjusted 
in such a manner that hard particulates, such as metal carbides, borides, 
nitrides or oxides, with higher elastic modulii than steel are added to 
raise the resultant elastic modulus of the FGM coating. Carbon content can 
also be adjusted throughout the FGM layer in such a manner that a gradient 
of martensite start (Ms) temperatures is developed that will enable the 
resultant residual stress gradient in the article to be controlled.

BEST MODE FOR CARRYING OUT THE INVENTION 
As used in this description and in the claims, the term "rolling contacts" 
describes the area of contact between two bodies wherein the motion of one 
surface relative to the other surface can be described with a linear 
velocity as well as a rotational velocity. 
The term "rolling contacts" includes contacts where the surface velocities 
at the point of contact are equal and parallel, such as for example, in 
anti-friction bearings. 
The term "rolling/sliding contacts" describes a similar contact, however, 
there is significant difference in the surface velocities of the two 
contacting surfaces that causes a sliding component of the contact, for 
example, such as in gears. 
As used in this description and in the claims, the term "sliding contacts" 
describes the area of contact between two bodies where one surface is 
stationary and the motion of one surface relative to the second surface is 
described with a velocity vector which coincides with the contact 
interface. Fuel injector plunger, barrel assemblies, and journal bearings 
are some examples of components subjected to sliding contacts. 
As used in this description and in the claims, the term "abrasion contacts" 
describes a contact between two surfaces where material is removed from 
one surface by the combined force and velocity of the second surface. This 
material removal can be large, for example, in abrasive wear of GET's, or 
small and localized, for example, in the scoring of gear teeth. 
As used in this description and in the claims, the term "bending contacts" 
describes the area of contact between two bodies where a load is applied 
in a cantilever manner to the component, which creates resultant stresses 
in the component away from the area of contact. For example, GET's such as 
bucket tips are subjected to bending contacts. 
As used in this description and in the claims, the term "functionally 
graded materials" means a material which has a continuously varying 
composition and/or microstructure from one boundary to another. 
As used in this description and in the claims, the term "elastic modulus" 
means the elastic modulus as determined by ASTM Method E111, "Standard 
Test Method for Young's Modulus, Tangent Modulus and Chord Modulus". 
The term "thermal spray deposition", as used herein means the thermal spray 
techniques such as, oxyacetylene torch thermal spray, gas stabilized 
plasma spray, water stabilized plasma spray, combustion thermal spray, and 
high velocity oxygen fueled spray (HVOF). It must be understood that the 
thermal spray techniques are not limited to the above enumerated methods 
and that other alternative thermal spray techniques known to those skilled 
in the art may be employed. A technical publication titled "Thermal Spray 
Processing of FGMs", by S. Sampath, H. Herman, N. Shimoda, and T. Saito, 
published in the MRS Bulletin, pages 27-31, January 1995, and which is 
incorporated herein by reference, discloses a thermal spray method of 
depositing FGMs. A water stabilized plasma spray apparatus is described in 
U.S. Pat. No. 4,338,509,which is incorporated herein by reference. 
Another technical article titled "Advanced Thermal Spray Coatings for 
Corrosion and Wear Resistance", by R. C. Rucker, Jr., and A. A. Ashary, 
published in Advances in Coatings Technologies for Corrosion and Wear 
Resistant Coatings, 1995, pages 89-98 describes various thermal spray 
processes, and is incorporated herein by reference. 
The term "bonded" as used herein means a bond of a thermally sprayed 
coating to a substrate due to mechanical interlocking with asperities on 
the surface of the substrate. This mechanical interlocking is obtained by 
roughening the surface of the substrate, say, by grit blasting. The bond 
strengths of coatings are measured by ASTM Recommended Practice C633. 
In the preferred embodiment of the present invention, a component having a 
surface is provided. Desirably, the surface is clean and free of 
contaminants. Cleaning can be accomplished a various means known to one 
skilled in the art, including cleaning by solvents, de-greasing, grit 
blasting, chemical etching and ultra-sonic cleaning. 
In the preferred embodiment of the present invention, an FGM is desirably 
thermally sprayed on the substrate surface, and preferably, sprayed by gas 
or water stabilized plasma spray. An FGM coating is formed on the surface. 
The FGM coating desirably has a thickness in the range of about 0.5 mm to 
about 20 mm. A thickness less than 0.5 mm is undesirable because it is too 
thin to tailor a modulus profile by varying FGM composition. A thickness 
greater than 20 mm is undesirable because it represents a waste of labor 
and materials. 
In the preferred embodiment of the present invention, the FGM coating also 
has a plurality of material compositions. The FGM coating further has a 
plurality of elastic modulus profiles. The FGM coating can further have a 
plurality of carbon gradient profiles. These carbon gradient profiles will 
create a gradient of martensite start (Ms) temperatures which can be used 
in alone or in conjunction with the elastic modulus profiles to create 
residual stress profiles that can improve the performance of the 
component. Desirably, the elastic modulus and carbon gradient profiles 
vary at various locations on the component surface depending on the amount 
and severity of the contact that the component is subjected to in the 
actual application. Preferably, the shape of the elastic modulus curve 
versus the thickness of the coating is also tailored to provide maximum 
load bearing capacity for a given deflection. The shape of the residual 
stress curve will be tailored to provide maximum compressive residual 
stresses at the surface and in the near surface material. The elastic 
modulus profile consists of a plurality of elastic modulii at a plurality 
of corresponding points within that thickness. The elastic modulii are 
preferably in the range of from about 28 Mpsi to about 60 Mpsi, as used 
herein, the unit "Mpsi" means million pounds per square inch. 
There can be two alternative embodiments of the present invention. The 
first embodiment involves components where the surface material wears away 
and is consumed during the life of the component. Track rollers, track 
links, and ground engaging tools are examples of these types of 
components. The second embodiment involves components where the part 
geometry is intended to remain essentially intact for the entire life of 
the component. Gears, bearings and camshafts are examples of this version. 
It is recognized that there will be some small amount of wear experienced 
in these components during their life, but it is minimal and generally 
less than 0.25 mm. The embodiment utilized will depend on the type of 
application and the type of applied contact for that particular component. 
Another aspect of the second embodiment is that the FGM carbon gradient 
profile in conjunction with the elastic modulus profile can provide 
beneficial residual stress profiles to improve component life. There is 
generally no need to control the carbon gradient profile in the first 
embodiment, since the surface material will be worn away during the life 
of that component. 
The article with the appropriate functionally graded material (FGM) coating 
shall be heat treated. In the case of an FGM where there is no significant 
difference between the carbon content of the FGM layer or the base 
material, the component shall be austenitized by any means available to 
one skilled in the art of heat treating such as furnace heating or 
induction heating, and so forth. The temperature shall be selected such 
that after austenitization, the matrix shall consist of austenite or 
austenite with carbides, nitrides or oxides. This temperature is typically 
27.7.degree. C. (50.degree. F.) to 55.6.degree. C. (100.degree. F.) above 
the Ac.sub.3 temperature for hypoeutectoid steels and the Ac.sub.1 
temperature for hypereutectoid steels. The time shall be selected such 
that full austenitization is accomplished within all sections of the 
component. The component shall them be quenched in a medium which will 
effect a martensitic transformation in the FGM layer. The cooling rate 
reduces as one traverses from a component's surface to the component's 
core. The percentage of martensitic transformation will also diminish from 
the surface to core. Hardenability should be selected commensurate with 
component size to match hardness, strength, and microstructure of the 
finished article in accordance with engineering/design requirements. 
In the case of an FGM where there is a carbon gradient in the near surface 
FGM, the component shall be austenitized by any means available to one 
skilled in the art of heat treating such as furnace heating or induction 
heating, and so forth. The temperature shall be selected to fully 
austenitize the core material, as well as the FGM layer. The temperature 
is typically 27.7.degree. C. (50.degree. F.) to 55.6.degree. C. 
(100.degree. F.)above the Ac.sub.3 temperature for the core material. For 
a steel with 0.20 weight percent carbon, the typical temperature is 
approximately 871.degree. C. (1600.degree. F.) The time shall be selected 
such that full austenitization of both FGM case and core material is 
achieved within all sections of the component. The article shall them be 
quenched in a medium that will effect a martensitic transformation in the 
FGM layer and the core material as hardenability allows. The cooling rate 
reduces as one traverses from a component's surface to the component's 
core. The percentage of martensitic transformation will also diminish from 
the surface to core. Hardenability should be selected commensurate with 
component size to match hardness, strength and microstructure of the 
finished article in accordance with engineering/design requirements. 
In the first embodiment of the present invention we have a component, such 
as a track roller, track link or ground engaging tool, with an FGM coating 
layer having a thickness of around 3 mm (0.118 inches) to 20 mm (0.78 
inches). The elastic modulii being in the range of about 15% to about 30% 
greater in the initial 25% of the coating thickness as measured from the 
surface of the coating as compared to a final 25% of the coating thickness 
as measured from the surface of the coating as shown in Tables A2, B2, and 
C2 and the respective graphical representations in FIG. 1, 2, and 3. One 
skilled in the art can develop suitable elastic modulus profiles for a 
certain type of a contact situation without undue experimentation by 
simply conducting a finite element analysis (FEA) of the component in a 
dynamic load situation by computer simulation. An elastic modulus less 
than about 28 Mpsi is unachievable when utilizing ferrous-based materials. 
An elastic modulus greater than 60 Mpsi is undesirable because it is 
impractical to obtain and represents an unnecessary waste of labor and 
resources for the intended component applications. 
Referring now to FIG. 4, in the preferred embodiment for the first 
embodiment of wear components that are subjected to abrasive contacts, a 
functionally graded material (FGM) is thermally sprayed on the surface of 
a component that forms an FGM coating, the FGM coating having a thickness, 
a plurality of material compositions, and a sequence of two to four 
elastic modulus profiles. For descriptive purposes there shall be four 
profile ranges, but sequential profiles may be identical, thus yielding 
the appearance of two profile ranges in the FGM layer, similar to that 
shown in FIG. 2. FIG. 4 reveals both an approximate upper range of modulus 
profiles and a lower range of modulus profiles versus depth from the 
surface of the component. 
The component is subject to one or more of rolling, sliding, abrasion and 
bending contacts. The first elastic modulus profile is in a range from 
about 28 Mpsi to about 60 Mpsi from the surface of the coating to about 
15% of the coating thickness as measured from the surface of the coating. 
The second elastic modulus profile is in a range from about 35 Mpsi to 
about 60 Mpsi from the surface of the coating from about 15% to about 65% 
of the coating thickness as measured from the surface of the coating. The 
third elastic modulus profile in a range from about 45 Mpsi to about 28 
Mpsi from the surface of the coating from about 65% to about 85% of the 
coating thickness as measured from the surface of the coating and the 
fourth elastic modulus profile in a range from about 32 Mpsi to about 28 
Mpsi from the surface of the coating to about 85% from about 100% of the 
coating thickness as measured from the surface of the coating. Another 
elastic modulus profile has it's first elastic modulus profile in a range 
from about 30 Mpsi to about 60 Mpsi from the surface of the coating to 
about 15% of the coating thickness as measured from the surface of the 
coating. The second elastic modulus profile is in a range from about 30 
Mpsi to about 60 Mpsi from about 15% to about 65% of the coating thickness 
as measured from the surface of the coating. The third elastic modulus 
profile is in a range from about 30 Mpsi to about 45 Mpsi from the surface 
of the coating from about 65% to about 85% of the coating thickness as 
measured from the surface of the coating and the forth elastic modulus 
profile is in a range from about 30 Mpsi to about 32 Mpsi from the surface 
of the coating from about 85% to about 100% of the coating thickness as 
measured from the surface of the coating. 
Prior to the Applicants' invention and as previously stated, these wear 
components were through hardened or case hardened by processes such as 
induction or flame hardening. These processes resulted in hardness 
gradients from the surface to core, but did not have modifications of 
elastic modulus profiles, as shown in FIG. 5. 
In the second embodiment of the present invention, a typical component 
would be a gear, bearing, or camshaft, with an FGM coating layer having a 
thickness of around 0.5 mm (0.02 inches) to 4 mm (0.16 inches). The 
components relating to the second embodiment are designed for transmission 
of power, and are designed such that the entirety of the component is 
intended to remain intact for the life of the component. The case 
hardening process is typically performed using a diffusion controlled 
carburizing process. The resultant carbon gradient profile and elastic 
modulus profile are shown in FIG. 6. The resultant residual stress profile 
is shown on FIG. 7. 
Referring now to FIG. 6, the percent of carbon decreases as the depth of 
the component increases while the elastic modulus remains constant. As 
shown in FIG. 7, there is a significant amount of residual stress at a 
relatively low depth. 
Referring now to FIG. 8, the elastic modulus and the percent of carbon 
content are illustrated for a component of the second embodiment having a 
FGM coating. The percent of carbon in the FGM coating is very similar to 
that found in the carburized component which could have a carbon profile 
gradient as illustrated in FIG. 6. In this example of FGM, the carbon 
gradient mimics that of a conventionally carburized component, but in 
addition, the elastic modulus profile is modified. The resultant residual 
stress gradient profile is depicted in FIG. 9. The elastic modulus can be 
described in a series of four profiles. The first elastic modulus profile 
is in a range from about 28 Mpsi to about 45 Mpsi from the surface of the 
coating to about 15% of the coating thickness as measured from the surface 
of the coating. The second elastic modulus profile is in a range from 
about 35 Mpsi to about 45 Mpsi from about 15% to about 65% of the coating 
thickness as measured from the surface of the coating. The third elastic 
modulus profile in a range from about 45 Mpsi to about 28 Mpsi from about 
65% to about 85% of the coating thickness as measured from the surface of 
the coating and the fourth elastic modulus profile in a range from about 
32 Mpsi to about 28 Mpsi to about 85% to about 100% of the coating 
thickness as measured from the surface of the coating. 
The first elastic modulus profile is substantially lower at the surface of 
the coating than at 15% of the coating thickness as measured from the 
surface of the coating. In addition, the third elastic modulus profile is 
substantially higher at about 65% of the coating thickness as measured 
from the surface of the coating to about 85% of the coating thickness as 
measured from the surface of the coating. 
As shown in FIG. 9, the subsurface residual stress of the thermally sprayed 
FGM coating is at least a factor of two times the amount of residual 
stress of a carburized component without a thermally sprayed FGM coating. 
Referring now to FIG. 10, a FGM layer is applied to a component in such a 
manner that the carbon profile is modified in such a manner that the 
resultant residual stress is modified from that of a conventionally 
carburized component such as depicted in FIGS. 6 and 7. The carbon content 
can be describe in a series of four profiles. The first carbon content 
profile is in a range from about 0.75% to about 0.95% weight carbon from 
the surface of the coating to about 15% of the coating thickness as 
measured from the surface of the coating. The second carbon content 
profile is in a range from about 0.95% to about 0.35% weight carbon from 
the surface of the coating from about 15% to about 65% of the coating 
thickness as measured from the surface of the coating. The third carbon 
content profile is in a range from about 0.5% to about 0.1% weight carbon 
from the surface of the coating from about 65% to about 85% of the coating 
thickness as measured from the surface of the coating and the fourth 
elastic modulus profile in a range from 0.35% to about 0.1% weight carbon 
from the surface of the coating from about 85% to about 100% of the 
coating thickness as measured from the surface of the coating. The elastic 
modulus profile is not modified and remains constant throughout the 
coating. The resultant change to the residual stress is most significant 
at the surface, having increased by almost a factor of 2 over the standard 
carburized component, as shown in FIG. 11. 
Referring now to FIG. 12, an FGM coating is applied to a component such 
that both the carbon gradient profile and elastic modulus profile are 
modified from that of a conventional component. The carbon content can be 
describe in a series of four profiles. The first carbon content profile is 
in a range from about 0.75% to about 0.95% weight carbon from the surface 
of the coating to about 15% of the coating thickness as measured from the 
surface of the coating. The second carbon content profile is in a range 
from about 0.95% to about 0.35% weight carbon from the surface of the 
coating from about 15% to about 65% of the coating thickness as measured 
from the surface of the coating. The third carbon content profile is in a 
range from about 0.5% to about 0.1% weight carbon from the surface of the 
coating from about 65% to about 85% of the coating thickness as measured 
from the surface of the coating and the fourth elastic modulus profile in 
a range from 0.35% to about 0.1% weight carbon from the surface of the 
coating to about 85% to about 100% of the coating thickness as measured 
from the surface of the coating. Another illustration of carbon content, 
as a percentage, from the surface of the coating can be found in FIG. 13. 
Both the approximate upper carbon content range and lower carbon content 
range are depicted in relationship to depth from the surface of the 
component. 
In addition, the elastic modulus can be describe in a series of four 
profiles, in the same manner as illustrated in FIG. 8. The first elastic 
modulus profile is in a range from about 28 Mpsi to about 45 Mpsi from the 
surface of the coating to about 15% of the coating thickness as measured 
from the surface of the coating. The second elastic modulus profile is in 
a range from about 35 Mpsi to about 45 Mpsi from the surface of the 
coating from about 15% to about 65% of the coating thickness as measured 
from the surface of the coating. The third elastic modulus profile in a 
range from about 45 Mpsi to about 28 Mpsi from the surface of the coating 
from about 65% to about 85% of the coating thickness as measured from the 
surface of the coating and the fourth elastic modulus profile in a range 
from about 32 Mpsi to about 28 Mpsi from the surface of the coating from 
about 85% to about 100% of the coating thickness as measured from the 
surface of the coating. Another illustration of an approximate upper range 
of elastic modulus versus depth and an approximate lower range of elastic 
modulus versus depth, as a percentage, from the surface of the coating can 
be found in FIG. 14. 
As shown in FIG. 15, the surface having a thermally sprayed FGM coating 
with both the above described elastic modulus profiles and carbon content 
profiles has both a surface residual stress and subsurface residual stress 
that is at least a factor of two greater than a case hardened or 
carburized component. In addition, the depth of the subsurface residual 
stress is in a range of about 70% to about 90% greater than the subsurface 
residual stress of a case hardened or carburized component. 
In both embodiments of the present invention, the preferred ceramic is 
desirably one of titanium carbide (TiC), tungsten carbide (WC), Cr2C3, 
MoFeB, BC4 and mixtures thereof. The term "cermet" as used herein, 
describes a type of material that includes a ceramic component and a metal 
component. Examples of cermets include Nickel-Chromium-Aluminum-Yttria 
alloy (NiCrAlY), Nickel-Chromium (NiCr) with Partially Stabilized Zirconia 
(PSZ), NiCrAlY with ZrO2 and Y203, nickel with Al203, tungsten carbide, 
and cobalt-chrome carbide. It must be understood that the present 
invention is not limited to any of the above enumerated materials and one 
skilled in the art may select other ceramic, cermet, or metallic 
materials. 
The following Examples A, B, and C illustrate the process of the first 
embodiment of the present invention, as applied to the thermal spraying of 
an FGM coating on the substrate surface of a track roller for an 
earthworking machine, to obtain a tailored elastic modulus profile, which 
results in enhanced rolling, sliding and abrasion performance. 
The following materials were used for thermally spraying an 8 mm thick FGM 
coating on a SAE Grade 41B35 substrate of a track roller by gas stabilized 
plasma spray: M4, TiC, WC, and A4635 steel alloy. The composition of the 
M4 material was as follows, by weight percent: C 1.5%, Si 0.39%, Mn 0.40%, 
P 0.015%, S 0.14%, Cr 4.57%, Ni 0.08%, Mo 4.58%, Cu 0.05%, Al 0%, Co 
0.03%, V 3.9%, W 5.8%, N 0.04%, O 90 ppm and balance iron. The M4 material 
is supplied by Anval Corporation under the trade name "Anval M4". The 
composition of the A4635 material was as follows, by weight percent: C 
0.35%, Si 0.005%, Mn 0.17%, P 0.006%, S 0.015%, Cr 0.03%, Ni 1.78%, Mo 
0.54%, Cu 0.09%, Al 0%, Co 0%, V 0%, W 0%, N less than 0.001%, O 1100 ppm 
and balance iron. The A4635 material is manufactured by Hoeganaes 
Corporation by mixing a metal powder made by Hoeganaes having a trade name 
"Ancorsteel A4600V" with 0.5% by weight carbon. Similarly, A4690, A4670, 
and A4625 are manufactured by mixing "Ancorsteel A4600V" with 0.90, 0.70, 
0.25 percent by weight carbon, respectively. 
EXAMPLE A 
An 8 mm thick FGM coating was deposited with the following compositional 
gradient profile on a SAE Grade 41B35 substrate, as shown in Table A1: 
TABLE A1 
______________________________________ 
Starting 
Depth 
from Ending Depth Layer Composition 
Surface from Surface (volume %) 
______________________________________ 
0 mm 1 mm M4 with 30% TiC 
1 mm 3 mm M4 with 30% TiC 
graded to 100% M4 
3 mm 4 mm 100% M4 
4 mm 8 mm 100% M4 graded 
to 100% A4635 
______________________________________ 
The FGM coating has the following elastic modulus profile, as shown in 
Table A2: 
TABLE A2 
______________________________________ 
Starting 
Depth 
from Ending Depth 
Surface from Surface Elastic Modulus, Mpsi 
______________________________________ 
0 mm 1 mm 40 
1 mm 3 mm 40 graded to 30 
3 mm 4 mm 30 
4 mm 8 mm 30 
______________________________________ 
The elastic modulus gradient of the above FGM is shown graphically in FIG. 
1. 
EXAMPLE B 
An 8 mm thick FGM coating was deposited with the following compositional 
gradient profile on a SAE Grade 41B35 substrate, as shown in Table B1: 
TABLE B1 
______________________________________ 
Starting 
Depth 
from Ending Depth Layer Composition 
Surface from Surface (volume %) 
______________________________________ 
0 mm 4 mm 50% A4635 and 50% TiC 
4 mm 8 mm 50% A4635 and 50% TiC 
graded to 100% A4635 
______________________________________ 
The FGM coating has the following elastic modulus profile, as shown in 
Table B2: 
TABLE B2 
______________________________________ 
Starting 
Depth 
from Ending Depth 
Surface from Surface Elastic Modulus, Mpsi 
______________________________________ 
0 mm 4 mm 47.5 
4 mm 8 mm 47.5 graded to 30 
______________________________________ 
The elastic modulus gradient of the above FGM is shown graphically in FIG. 
2. 
EXAMPLE C 
An 8 mm thick FGM coating was deposited with the following compositional 
gradient profile on a SAE Grade 41B35 substrate, as shown in Table C1: 
TABLE C1 
______________________________________ 
Starting 
Depth 
from Ending Depth Layer Composition 
Surface from Surface (volume %) 
______________________________________ 
0 mm 1 mm M4 with 30% WC 
1 mm 3 mm M4 with 30% WC 
graded to 100% M4 
3 mm 4 mm 100% M4 
4 mm 8 mm 100% M4 graded to 
100% A4635 
______________________________________ 
The FGM coating has the following elastic modulus profile, as shown in 
Table C2: 
TABLE C2 
______________________________________ 
Starting 
Depth 
from Ending Depth 
Surface from Surface Elastic Modulus, Mpsi 
______________________________________ 
0 mm 1 mm 39 
1 mm 3 mm 39 graded to 30 
3 mm 4 mm 30 
4 mm 8 mm 30 
______________________________________ 
The elastic modulus gradient of the above FGM is shown graphically in FIG. 
3. 
The following Example D illustrates the process of the second embodiment of 
the present invention, as applied to the thermal spraying of an FGM 
coating on the substrate surface of a gear for an earthworking machine, to 
obtain a series elastic modulus profiles, which results in enhanced 
sliding performance. 
A 1.2 mm thick FGM coating was deposited with the following compositional 
gradient profile on a SAE Grade 4118 substrate, as shown in Table D1. 
TABLE D1 
______________________________________ 
Starting 
Depth 
from Ending Depth Layer Composition 
Surface from Surface (volume %) 
______________________________________ 
0 mm 0.2 mm A4670 graded to 
A4690 with 30% TiC 
0.2 mm 0.5 mm A4690 with 30% TiC 
graded to A4670 
with 30% TiC 
0.5 mm 0.8 mm A4670 with 30% TiC 
graded to A4625 with 
30% TiC 
0.8 mm 1.0 mm A4625 with 30% TiC 
graded to A4625 
1.0 mm 1.2 mm A4625 
______________________________________ 
The FMG coating has the following elastic modulus profile, as shown in 
Table D2 
TABLE D2 
______________________________________ 
Starting 
Depth 
from Ending Depth 
Surface from Surface Elastic Modulus, Mpsi 
______________________________________ 
0 mm 0.2 mm 30 graded to 40 
0.2 mm 0.8 mm 40 
0.8 mm 1.0 mm 39 graded to 30 
1.0 mm 1.2 mm 30 
______________________________________ 
The elastic modulus gradient and carbon composition gradients of the above 
FGM are shown graphically in FIG. 12. 
INDUSTRIAL APPLICABILITY 
The present invention is useful for making machine components that are 
constantly subjected to one or more of rolling, sliding, abrasion and 
bending contacts. Such components are typically various types of bearings, 
camshafts, planet shafts and gears used in engines and transmissions; 
track rollers, track links, track shoes and track links for the tracks of 
track-type tractors and earthmoving equipment and ground engaging tools. 
Typically, the types of components that would be subjected to the first 
embodiment of the present invention would include track rollers, track 
links, track bushings and ground engaging tools. Also, of the above listed 
components, typically, the types of components that would be subjected to 
the second embodiment of the present invention would include gears, 
bearings, planet shafts and camshafts. 
The present invention is particularly useful in enhancing the performance 
of components subjected to one or more of rolling, sliding, abrasion and 
bending contacts by using FGMs to provide FGM coated components which have 
a plurality of elastic modulus profiles as a function of coating thickness 
and component surface geometry. 
The present invention is also useful for making gun barrels, steel mill 
rolls, and mill rolls for calendering and paper converting. 
Other aspects, objects and advantages of this invention can be obtained 
from a study of the drawings, the disclosure and the appended claims.