Claims:
1. A system comprising:
a valve seat; and
a valve coupled to the valve seat, wherein at least one of the valve and the valve seat comprises:
a base comprising a plurality of dimples formed on a surface, and
a coating disposed on each of at least some dimples of the plurality of dimples, wherein each dimple of the at least some of the dimples has a depth greater than 50 micrometers, wherein the coating has a density greater than 98 percent of a theoretical density of the coating and a dilution less than 0.5 volume % of the coating.
2. The system of claim 1, wherein the depth of each dimple of the at least some of the dimples is greater than 100 micrometers.
3. The system of claim 1, wherein each dimple of the at least some of the dimples has a diameter greater than 50 micrometers.
4. The system of claim 1, wherein the plurality of dimples has a spatial density greater than 10 % of an area of the surface of the base.
5. The system of claim 1, wherein the coating is confined to a volume of each of the at least some of the dimples on the surface of the base.
6. The system of claim 1, wherein the base comprises a heat-affected zone bonded to the coating, wherein the heat-affected zone comprises a thickness less than 5 micrometers.
7. The system of claim 1, wherein the base comprises steel, nickel, a cobalt-based wear resistant alloy, a nickel-based alloy, an iron-based alloy, or combinations thereof.
8. The system of claim 1, wherein the base comprises a base substrate and a base layer comprising the surface, wherein the base layer has a thickness greater than 100 micrometers, a density greater than 98 percent of a theoretical density of the base layer, and a dilution less than 0.5 volume % of the base layer.
9. The system of claim 8, wherein at least one of the the base substrate or the base layer comprises steel, nickel, a cobalt-based wear resistant alloy, a nickel-based alloy, an iron-based alloy, or combinations thereof.
10. The system of claim 1, wherein the coating comprises copper, copper alloys, silver, silver alloys, aluminum alloys, or combinations thereof.
11. The system of claim 10, wherein the coating further comprises a solid-lubricant material comprising molybdenum disulfide, tungsten disulfide, graphite, calcium fluoride, barium fluoride, hexagonal boron nitride, or combinations thereof.
12. The system of claim 10, wherein the coating further comprises alumina, chromium carbide, cubic boron nitride, or combinations thereof.
13. An internal combustion engine comprising the system of claim 1.
14. A system comprising:
a valve seat; and
a valve coupled to the valve seat, wherein at least one of the valve and the valve seat comprises:
a base comprising a base substrate and a base layer, wherein the base layer comprises a plurality of dimples formed on a surface, wherein each dimple has a depth greater than 50 micrometers, wherein the base layer has a thickness greater than 100 micrometers, density greater than 98 percent of a theoretical density of the base layer, and a dilution less than 0.5 volume % of the base layer; and
a coating disposed on each of at least some dimples of the plurality of dimples, wherein the coating has a density greater than 98 percent of theoretical density of the coating and a dilution less than 0.5 volume % of the coating.
15. A method comprising:
disposing a coating on each of at least some dimples of a plurality of dimples formed on a surface of a base of at least one of a valve and valve seat using a friction surfacing process, wherein each dimple has a depth greater than 50 micrometers, wherein the coating has a density greater than 98 percent of a theoretical density of the coating and a dilution less than 0.5 volume % of the coating.
16. The method of claim 15, wherein disposing the coating comprises forging and traversing a rotating cylinder on the base, wherein the rotating cylinder comprises a coating material of the coating.
17. The method of claim 16, wherein the coating material comprises (a) a first material and (b) a solid-lubricant material, a second material, or a combination of the solid-lubricant and second materials.
18. The method of claim 17, wherein disposing the coating further comprises forming a gradient in the first material along a direction perpendicular to the base.
19. The method of claim 15, further comprising forming a plurality of dimples on the surface of the base, using a laser texturing method.
20. The method of claim 15, further comprising forming a base layer on a base substrate using a friction surfacing process, wherein the base layer comprises the surface.
The method of claim 15, further comprising machining the coating for altering a thickness of the coating, confining the coating to volume of each of the at least some dimples, or a combination thereof.
, Description:BACKGROUND
[0001] Embodiments of the present invention relate generally to coating of a valve system, and more particularly to a friction surfacing coating of a valve system.
[0002] Valves and valve seats of internal combustion engines are generally exposed to severe operating conditions during operation. The valve opens for intake of gases and closes for release of gases periodically during operation of the engine. An outer surface of the valve slides against an inner surface of the valve seat. Hence, an abrasion load is repeatedly applied to the contact surface of the valve seat. Consequently, over a period of time, both the surfaces of the valve and the valve seat are abraded. Wear related failures of the valve and valve seat components may affect the engine efficiency.
[0003] In conventional systems, valve and valve seat assemblies are generally lubricated using oil. The oil is not frequently retained in the valve and valve seats frequently resulting in loss of oil and decreased lubrication. As a result, the valve and the valve seats are subjected to wear.
[0004] Therefore, there is a need for an efficient, reliable, and durable valve system.
BRIEF DESCRIPTION
[0005] Embodiments of the invention are directed towards valve systems and an efficient method of coating.
[0006] In one embodiment, a system is disclosed. The system includes a valve seat and a valve coupled to the valve seat. At least one of the valve and the valve seat includes a base and the base includes a plurality of dimples formed on a surface of the base. A coating is disposed on each of at least some dimples of the plurality of dimples. A depth of the each of the dimples is greater than 50 micrometers. A density of the coating is greater than 98 % of a theoretical density of the coating and a dilution of the coating is less than 0.5 volume % of the coating.
[0007] In one embodiment, a system is disclosed. The system includes a valve seat and a valve coupled to the valve seat. At least one of the valve and the valve seat includes a base that includes a base substrate and a base layer. The base layer has a thickness greater than 100 micrometers, density greater than 98 percent of a theoretical density of the base layer, and a dilution less than 0.5 volume % of the base layer. The base layer includes a plurality of dimples formed on a surface of the base layer. A coating is disposed on each of at least some dimples of the plurality of dimples. A depth of the each of the dimples is greater than 50 micrometers, a density of the coating is greater than 98 % of a theoretical density of the coating and a dilution of the coating is less than 0.5 volume % of the coating.
[0008] In one embodiment, a method is disclosed. The method includes forming a coating on a base of at least one of a valve and a valve seat of a system. The coating is formed on each of at least some dimples of a plurality of dimples on a surface of a base, using a friction surfacing process. Each dimple has a depth greater than 50 micrometers. The coating has a density greater than about 98 % of theoretical density of the coating and a dilution less than 0.5 volume % of the coating.
DRAWINGS
[0009] These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the disclosure that is provided in connection with the accompanying drawings.
[0010] FIG. 1 is a schematic cross-sectional view of a system including a valve and valve seat according to an embodiment of the present invention;
[0011] FIG. 2 is a schematic cross-sectional view of a base according to an embodiment of FIG. 1;
[0012] FIG. 3 is a perspective view of a friction surfacing apparatus according to some embodiments of the present invention;
[0013] FIG. 4 is a schematic representation of a base having a plurality of dimples formed on a surface according to an embodiment of the present invention;
[0014] FIG. 5 is a schematic cross-sectional view of a base and a coating according to an embodiment of the present invention;
[0015] FIG. 6 is a schematic cross-sectional view of a base and a coating according to another embodiment of the present invention;
[0016] FIG. 7 is a schematic cross-sectional view of a pin tool according to an embodiment of the present invention;
[0017] FIG. 8 is a schematic cross-sectional view of a pin tool according to another embodiment of the present invention;
[0018] FIG. 9 is a schematic cross-sectional view of a base and a coating according to an embodiment of the present invention; and
[0019] FIG. 10 is a schematic cross-sectional view of an internal combustion engine according to an embodiment of the present invention.
DETAILED DESCRIPTION
[0020] Aspects of the present invention will now be described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below with reference to preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
[0021] In the following description, whenever a particular aspect or feature of an embodiment of the invention is said to comprise or consist of at least one element of a group and combinations thereof, it is understood that the aspect or feature may comprise or consist of any of the elements of the group, either individually or in combination with any of the other elements of that group.
[0022] In the following specification and the claims that follow, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
[0023] Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” or “substantially,” may not be limited to the precise value specified, and may include values that differ from the specified value. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value.
[0024] An aspect of the present invention is directed to a coating for a valve system. Valve systems may be used in different types of engines such as, for example, internal combustion engines and reciprocating engines. Failure of valves and valve seats can affect operation of the engines. Valve and valve seat damage may occur due to wear failure, valve face recession, fatigue failure, thermal fatigue, erosion/corrosion of valves and valve seats, overheating of valves and valve seats, and carbon deposits on valves and valve seats.
[0025] Intake (inlet) valves or exhaust valves of internal combustion engines engage with corresponding valve seats, when the valves are closed during a portion of the engine operating cycle. An improper positioning, orientation, or formation of the valve and valve seat combination due to manufacture defects or operational wear may adversely affect engine compression ratio and thereby affect the engine efficiency, performance (horsepower), exhaust emissions, and engine life.
[0026] FIG. 1 is a schematic sectional view of a system 100 in accordance with some embodiments of the present invention. The system 100 includes a valve seat 110 and a valve 120 coupled to the valve seat 110. As used herein, the phrase “valve coupled to the valve seat” means that the valve 120 and the valve seat 110 operate as a pair during the operation of the system 100 and does not necessarily indicate any physical bonding between the valve 120 and the valve seat 110. The exemplary valve 120 and valve seat 110 may be suitable for any combustion applications that include, but not limited to, internal combustion engines and reciprocating engines. At least one of the valve seat 110 and the valve 120 includes a base 130 that includes a plurality of dimples 131 on a surface 132. In some embodiments, a coating 140 may be provided on each of some dimples 134 among the plurality of dimples 131. As used herein, the term “coating” on each dimple 134 refers to the coating material in the dimple 134. In some embodiments, the coating 140 may be in the form of a layer on the entire surface 132 of the base 130. In some specific embodiments, the coating 140 may be provided on each dimple 131.
[0027] Each dimple 131 has a depth greater than 50 micrometers. A density of the coating 140 is greater than 98 % of a theoretical density of the coating 140. As used herein, the term “theoretical density of the coating” is defined as the mass per volume of the material of the coating 140, excluding all the pores in the coating. A dilution of the coating 140 is less than 0.5 volume % of the coating 140. As used herein, a “dilution of the coating 140” is referred to as an inclusion of any impurity, such as, for example, any other material other than a coating material of the coating 140. Some embodiments of the present invention are related to a method of providing the coating 140 on each dimple 134. In some embodiments, the coating 140 is formed using a friction surfacing method.
[0028] FIG. 2 is a schematic cross-sectional view of the base 130 according to an embodiment of FIG. 1. As discussed previously, the base 130 includes the plurality of dimples 131 formed on the surface 132. In some embodiments, a coating 140 may be provided on each of some dimples 134 among the plurality of dimples 131. In some specific embodiments, the coating 140 may be provided on each of the plurality of dimples 131.
[0029] Referring to FIG. 3, a perspective view of a friction surfacing apparatus 200 is illustrated according to some embodiments of the present invention. The friction surfacing apparatus 200 includes a movable pin tool 210. In the illustrated embodiment, the pin tool 210 has a substantially cylindrical, rod-like shape. The pin tool 210 may be a solid rod or may be partially or entirely hollow. The diameter of the pin toll 210 may vary depending on the application. In some embodiments, the diameter of the pin tool 210 is in a range from about 0.50 mm to about 50 mm.
[0030] The pin tool 210 is coupled to a drive mechanism (not shown), such as, for example, a spindle. The drive mechanism is operable for rotating the pin tool 210 about an axis 212. Typically, the pin tool 210 is rotated at a speed in a range from about 100 revolutions per minute (rpm) to about 10,000 rpm during the friction surfacing process. Rotation of the pin tool 210 in conjunction with a forging load transmitted between the pin tool 210 and the surface 132 of the base 130, generates a frictional heat and thermo-mechanical work. As a result, the pin tool 210 is subjected to frictional heat at a temperature below tool melting point, causing plasticization and deposition of material of the pin tool 210 on each dimple 134 formed on the surface 132 of the base 130. The amount of material deposited by the pin tool 210 may be dependent on the rotational speed of the pin tool 210, the feed rate of the pin tool 210, and the traverse speed of the friction surfacing apparatus 200. The pin tool 210 may be made of a material that is same as, similar to, or dissimilar from a material of the base 130. For example, if the base 130 is made of a metal or metal alloy, the pin tool 210 can be made of the same metal or metal alloy, or similar metal or metal alloy, or dissimilar material that provides a desired characteristic when the pin tool material is deposited on at least some dimples 134 on the surface 132 of the base 130.
[0031] During operation, the pin tool 210 is fed at a desired feed rate. The pin tool 210 is rotated and traversed along the surface 132 of the base 130. In some embodiments, the feed rate may in a range from about 2 millimeters per minute (mm/minute) to about 100 mm/minute. It should be noted that the feed rate of the pin tool 210 may vary based upon pin tool material(s) and the material(s) of the base 130.
[0032] Further, during operation, a temperature of a tip of the pin tool 210 is maintained at a range in which the pin tool material is substantially plastic. For example, the temperature of the tip of the pin tool 210 may be maintained in a range from about 800° C to about 1000° C for copper and copper alloys; from about 875° C to about 1075° C for different steels and nickel alloys, and from about 1100° C to about 1300° C for titanium and titanium alloys.
[0033] As disclosed previously, the base 130 includes a plurality of dimples 131 on the surface 132. As the pin tool 210 is traversed along the base 130, the plasticized metal, metal alloy, or other material of the pin tool 210 is deposited to forming a coating of the pin tool material on the surface 132 of the base 130. The pin tool material is coated on some dimples 134 of the plurality of dimples 131. The pin tool 210 may be traversed along the surface 132 of the base 130 at a rate that is sufficient to deposit a desired amount of material on each dimple 134. For example, in some embodiments, the pin tool 210 may traverse along the surface 132 of the base 130 at a rate in a range from about 2 mm/minute to about 400 mm/minute.
[0034] A continuous forging action on the pin tool 210 enhances the mechanical bond between the deposited pin tool material and the base 130, refines the microstructure of deposited pin tool 210 material, and minimizes any flash during operation. The localized plastic deformation of the pin tool 210 results in a substantially crystalline microstructure and low porosity. The pin tool 210 may be subjected to sequential passes to form a monolithic or graded coating. In some other embodiments, linear, angular and/or contoured coating may be formed.
[0035] In accordance with the embodiments of the present invention, the friction surfacing apparatus 200 may be used to deposit similar or dissimilar material such as titanium alloys, nickel-based alloys, iron based alloys (including steel), copper-based alloys, aluminum-based alloys, cobalt based alloys, and the like on a wide variety of base materials.
[0036] The exemplary friction surfacing method described herein provides benefits including: 1) minimal solidification cracking, porosity, or segregation; 2) a fine, hot-worked metallurgical structure; 3) mechanical properties of the deposited or bonded zone material that are equivalent to or better than the base material; 4) lower heat input to the base material to reduce residual stresses and distortion which does not adversely affect the structure and properties of the base material and 5) ability to tailor the local chemistry, metallurgical structure, and mechanical properties of specific areas or coating of the components.
[0037] FIG. 4 illustrates a schematic representation of the base 130 having the plurality of dimples 131 formed on the surface 132 according to an embodiment of the present invention. The dimples 131 are recesses formed on the surface 132 of the base 130. The shape and size of the dimples 131 may vary depending on the application. In some embodiments, shape of each dimple 131 may be a hemi-sphere, parabola, cylindrical, conical, square, rectangle, or any combinations thereof. In some embodiments, the dimples 131 have a spherical cross-sectional area 150. Non-limiting examples of dimples 134 may include hemispherical dimples 152, parabola shaped dimples 154, cylindrical dimples 156, and conical dimples 158. In some embodiments, some dimples 134 may have an oval cross-sectional area 160.
[0038] In some embodiments, a depth or thickness “t” of each dimple 131 is greater than 50 micro meters. In some other embodiments, the depth “t” of each dimple 131 is greater than 100 micrometers. In certain embodiments, the depth “t” is greater than 500 micrometers. In certain other embodiments, the depth “t” is in a range from about 100 micrometers to about 2 millimeters. In some other embodiments, the depth “t” is in a range from about 200 micrometers to about 1.5 millimeters.
[0039] In some embodiments, a diameter “d” of each dimple 134 is greater than 50 micro meters. In some other embodiments, the diameter “d” of each dimple 134 is greater than 100 micrometers. In certain embodiments, the diameter “d” is greater than 500 micrometers. In certain other embodiments, the diameter “d” is in a range from about 50 micrometers to about 4 millimeters. In some embodiments, the diameter “d” is in a range from about 100 micrometers to about 2 millimeters. In some embodiments, a depth “t” to diameter “d” ratio of each dimple 134 is in a range from about 0.1 to about 100. In some specific embodiments, the depth “t” to diameter “d” ratio of each dimple is in a range from about 0.5 to about 10.
[0040] In some embodiments, an aspect ratio of the cross-section of the oval dimple 160 is greater than 1. As used herein, an aspect ratio of the cross-section of the oval dimple 160 is defined as a length “l” to width “w” ratio of the oval dimple 160. In some embodiments, the aspect ratio of the oval dimple 160 is greater than 10. In certain embodiments, the aspect ratio of the oval dimple 160 is greater than 100.
[0041] In some embodiments, the plurality of dimples 131 has a spatial density greater than 10 % of area of the surface 132 of the base 130. The term “spatial density” as used herein refers to a ratio of an area occupied by the plurality of dimples 131 to the total area of the surface 132. In some embodiments, the spatial density is in a range from about 10 % to 20 % of area of the surface 132.
[0042] FIG. 5 is a schematic cross-sectional view of the base 130 according to an embodiment of the present invention. In the illustrated embodiment, each dimple 134 is provided with the coating 140. In some embodiments, each dimple 134 is substantially filled with the coating 140. In the illustrated embodiment, the coating 140 is confined only to the volume of each dimple 134. In other words, the coating 140 is not provided to the areas of the surface 132 that are not occupied by the dimples.
[0043] FIG. 6 is a schematic cross-sectional view of the base 130 according to another embodiment of the present invention. In the illustrated embodiment, each dimple 134 is provided with the coating 140. Additionally, the coating 140 is also provided to the areas of the surface 132 that are not occupied by the dimples.
[0044] In some embodiments, a density of the coating 140 is greater than 98 % of a theoretical density of the coating 140. As used herein, the term “theoretical density” defined as the mass per volume of the material of the coating 140, excluding all the pores. The theoretical density may be calculated from the crystallographic data of the material composition of the coating 140.
[0045] In the exemplary friction surfacing method disclosed herein, a mechanical mixing or stirring between the base material and the coating material is substantially less compared to some other coating methods, such as, for example, sputtering. The exemplary friction surfacing method results in minimal contamination of the coating 140 compared to other coating processes. In some embodiments, a dilution of the coating 140 is less than 0.5 volume% of the coating 140. In certain embodiments, the dilution is less than about 0.1 volume % of the coating 140.
[0046] With reference to both FIGS. 5 and 6, the base 130 includes a heat-affected zone 136 bonded to the coating 140. The heat-affected zone 136 has a thickness less than 5 micrometers. The heat-affected zone 136 is defined as the portion of the base 130 that is affected by the process of providing the coating 140. When a friction surfacing method is used to provide the coating 140 on the base 130, the heat-affected zone 136 is a top portion of the base 130 that is affected while providing the coating 140. A portion or zone 136 of the base 130 is said to be “heat-affected” if any physical or chemical characteristics of the portion/zone is changed to an extent greater than 5% compared to a remaining portion of the base 130 which is not affected by the coating process. The physical characteristics may include, for example, the structure, microstructure, and density of the heat affected zone. The chemical characteristics may include, for example, the material composition or the crystal structure of the heat affected zone 136.
[0047] In some embodiments, the heat-affected zone 136 is a very thin layer of the base 130. Such a thin heat-affected zone 136 is particularly advantageous compared to a thicker heat-affected zone because the thin heat-affected zone may include weak zones of coarse microstructure and low hardness where failure may be initiated. Therefore, in some embodiments, a well-adhering and effective coating 140 is provided on the base 130 without substantially changing the mechanical characteristics of the base 130 during the coating process. Therefore, a desired base may be designed before-hand without the need to accommodate any substantial changes during the process of coating. In some specific embodiments, a thickness of the heat-affected zone 136 of the base 130 is less than about 5 micrometers. In some embodiments, the thickness of the heat-affected zone 136 is less than about 2 micrometers.
[0048] In the embodiment of FIG. 5, the coating 140 is confined to the volume of the each dimple 134, the heat-affected zone 136 of base 130 is confined to the interface of the coating 140 that is disposed on each dimples 134. In the embodiment of FIG. 6, the coating 140 is disposed on the entire surface 132. In such an embodiment, the heat-affected zone 136 of the base 130 extends along the interface of the entire surface 132 with the coating 140.
[0049] As disclosed earlier, a function of the coating 140 is to provide lubrication between valves and valve seats, and hence reduce friction. Accordingly, in some embodiments, the coating 140 includes a soft material. As used herein, the term “soft material” refers to a material that either has reduced inherent hardness as compared to the material of the base 130 or may become softer than the materials of the base at the operating temperature of the valves and valve seats. Incorporation of a soft, high thermal conductivity material in the coating 140 further enhances heat-transfer between valves and valve seats. Non-limiting examples of the soft material include copper, copper alloys, silver, silver alloys, aluminum alloys.
[0050] In some embodiments, the coating 140 may include a solid-lubricant material and the soft material. As used herein, the term “solid-lubricant material” refers to a material that is in a solid state at an operating temperature and is capable of providing a lubricating action on surfaces where the solid-lubricant material is applied. A solid-lubricant material is particularly advantageous compared to a traditionally used liquid-lubricant material because the disposal and maintenance of the solid-lubricant material is much easier compared to the liquid-lubricant material. Non-limiting examples of the solid-lubricant material include molybdenum disulfide, tungsten disulfide, graphite, calcium fluoride, barium fluoride, hexagonal boron nitride, or any combinations thereof. In some specific embodiments, the solid-lubricant material includes molybdenum disulfide, tungsten disulfide, or a combination of both.
[0051] In some specific embodiments, the coating 140 may include a gradient of the soft material in the coating along a direction that is perpendicular to the base. For example, in certain embodiments, an amount of soft material may decrease along a direction from the base 130 to a top surface of the coating 140. In some other embodiments, the amount of soft material in the coating 140 may increase along the thickness (not shown) of the coating 140 from the base 130. A gradient of the soft material and the solid-lubricant material may be particularly advantageous to provide specific lubrication at specific locations along the thickness of the coating 140. In some specific embodiments, the coating 140 including a combination of the soft material and solid-lubricant material is provided on a base that includes a hard material such as, for example, steel, nickel based super alloys such as, for example, InconelTM and NimonicTM, cobalt-based wear resistant alloys, such as, for example, StelliteTM. In certain embodiments, the coating 140 including the soft material and the solid lubricating material may be confined to the volume of the dimples formed on the surface 132 of the base, as shown in FIG. 5. This is particularly advantageous as the surface 132 after coating, includes the soft material, the solid-lubricant material, and the hard material, thus providing both lubrication and wear resistance.
[0052] In some embodiments, the coating 140 may include a hard material and the soft material. As used herein, the term “hard material” of the coating 140 refers to a material that has enhanced inherent hardness compared to the material of the base 130. The hard material of the coating 140 enhances wear resistance of the coating 140. Non-limiting examples of the hard material of the coating 140 include alumina, chromium carbide, cubic boron nitride, or any combinations thereof. In some specific embodiments, the hard material of the coating 140 includes alumina, chromium carbide, or a combination of both.
[0053] In some specific embodiments, the coating 140 may include a gradient of the soft material along a direction that is perpendicular to the base 130. For example, in certain embodiments, an amount of the soft material may decrease along a direction from the base 130 to a top surface of the coating 140. In some other embodiments, the amount of soft material in the coating 140 may increase along the thickness of the coating 140 from the base 130.
[0054] In some embodiments, the coating 140 may include a soft material, a hard material, and a solid-lubricant material. In some further embodiments, the coating 140 may include a gradient of the soft material, solid-lubricant material, and/or hard material.
[0055] FIG. 7 shows a schematic sectional view of the pin tool 210 used to provide the coating 140 on the base 130 in accordance with an embodiment of the present invention. In the illustrated embodiment, the pin tool 210 includes two different materials 214, 216 that are disposed during the coating process. The materials 214, 216 may be selected such that the material 214 may be a first material and the material 216 may be a solid-lubricant material, a second material, or combination of the solid-lubricant material and the second material. Non-limiting examples include a soft material and a solid-lubricant material, or a soft material and a hard material, or a soft material, a hard material, and a solid-lubricant material. An exemplary soft material includes copper. An exemplary hard material may include alumina. Exemplary solid-lubricant materials include molybdenum disulfide and tungsten disulfide. A desired mixture of the materials 214, 216 is deposited on predefined locations of the base 130 by rotating the pin tool 210. The rotation of the pin tool 210 may be controlled to deposit different amounts of the materials 214, 216 depending on the application. While the illustrated embodiment shows only two materials 214, 216 to be deposited as a mixture, one skilled in the art would be able to envision additional materials depending on the application.
[0056] FIG. 8 is a schematic cross sectional view of the pin tool 210 in accordance with another exemplary embodiment. The pin tool 210 is configured to form the coating 140 having a graded compositional variation along a direction perpendicular to the base 130. Specifically, amount of the materials 214, 216 are graded in the pin tool 210 in a direction along the axis 212 perpendicular to the base 130 on which the coating 140 is to be deposited. As a result, the formed coating 140 includes a gradient in the amount of the materials 214, 216 deposited on the base 130, along the direction perpendicular to the base 130. In certain embodiments, the pin tool 210 includes a mixture of copper and alumina. In some embodiments, the pin tool 210 includes a mixture of copper and tungsten disulfide. In certain other embodiments, the pin tool 210 includes a mixture of copper, alumina, and molybdenum disulfide.
[0057] FIG. 9 is a schematic cross-sectional view of the base 130 and the coating 140 according to an embodiment of the present invention. The base 130 includes a base substrate 122 and a base layer 124 formed on the base substrate 122. In some embodiments, the base substrate 122 is formed on the base layer 124, using a friction surfacing process. The base layer 124 includes the surface 132 having the plurality of dimples 134. In some embodiments, the base substrate 122 and the base layer 124 have the same material composition. In some other embodiments, the base substrate 122 and the base layer 124 have different material composition. In certain embodiments, the base layer 124 may include a hard material. Non-limiting examples of the hard material include ceramic materials, composite materials, Stellite 12TM, Stellite 6TM, Triballoy 400TM, Nimonic 80ATM, WinsertTM, Pyromet 31TM, or any combinations thereof. In some embodiments, the base layer 124 may have a combination of hard materials, and the method described in FIG. 8 and FIG. 9 may be used to coat the base layer 124 with different combination of materials. The thickness of the base layer 124 may vary depending on the applications. The coating 140 is provided on the base layer 124.
[0058] In some embodiments, the thickness of the base layer 124 may be greater than 100 micrometers. In some other embodiments, the thickness of the base layer 124 is in a range from about 0.2 mm to about 10 mm. In some other embodiments, the thickness of the base layer 124 is in a range from about 0.5 mm to about 5 mm. In certain embodiments, the thickness of the base layer 124 is in a range from about 2 mm to about 4 mm. The base layer 124 may have a high density and low dilution. In some embodiments, a density of the base layer 124 is greater than 98 percent of a theoretical density of the base layer 124 and a dilution of the base layer 124 is less than 0.5 volume % of the base layer 124.
[0059] In the illustrated embodiment, the base substrate 122 includes a heat-affected zone 126 at the interface with the base layer 124. In some embodiments, a thickness of the heat affected zone 126 is less than 0.5 micrometer.
[0060] In some embodiments, the coating 140 includes a combination of the soft material and a solid-lubricant. In certain embodiments, the coating 140 may be confined to the volume of the dimples 134 formed on the surface 132 of the base layer 124.
[0061] Various methods may be used to form the dimples formed on the surface 132, such as, for example, lithographic techniques, machining, embossing, chemical etching, micro milling, shot blasting, electrical discharging, or ball end milling. In certain embodiments, a laser texturing method is used to create dimples on the base 130 layer 124. A laser surface texturing technique is particularly advantageous over other methods because laser texturing method is a fast and efficient process and may be used to form dimples of different geometries. For the laser texturing method, a pulsed laser may be used, such as, for example, an excimer laser. Surface of the sample may be cleaned before the laser etching step, using different methods. Further subsequent etching steps, such as, for example, chemical etching, may be carried out after the last etching step. Etched surfaces may be polished and cleaned using ultra sonication. In some embodiments, the dimples are cleaned by different methods, such as, for example, acid cleaning, for performing friction surfacing coating.
[0062] In some embodiments, the surface 132 of the base 130 and/or the coating 140 may be further subjected to post-coating treatments, such as, for example, machining to provide exact thickness, surface texture, surface material combination, or a combination thereof. For example, in some embodiments, the coating 140 may be formed on the dimples 134 and further on the portions of the surface 132 that are not occupied by the dimples. It may be desirable to confine the coating 140 to the volume of the dimples 134. In such embodiments, machining may be used to remove top portion of the coating 140 and also to remove coating 140 from portions of the surface 132 that are not occupied by the dimples.
[0063] FIG. 10 is a schematic view of an internal combustion engine 160 according to an embodiment of the present invention. The engine include an intake valve 168 coupled to a valve seat 169 and an exhaust valve 166 coupled to a valve seat 167. In some embodiments, the exhaust valve 166 and the valve seat 167 may operate at a higher temperature compared to the inlet valve 168 and the valve seat 169 of the combustion engine 160. For example, the exhaust valve 166 and the exhaust valve seat 167 may operate at a temperature in a range from about 350ºC to about 700ºC whereas the inlet valve 168 and the inlet valve seat 169 may operate at a temperature in a range from about 150ºC to about 300ºC.
[0064] The exemplary friction surfacing method disclosed herein may be used to coat any of the exhaust valve 166, inlet valve 168, and the valve seats 167, 169. The base of the coating may include any metal or alloy that is used to manufacture the exhaust valve 166, the inlet valve 168, and the valve seats 167, 169. In some embodiments, material of the base may include steel, nickel, a cobalt-based wear resistant alloy, a nickel-based alloy, an iron-based alloy, or any combinations thereof. Non-limiting examples include steel, nickel based super alloys such as, for example, InconelTM and NimonicTM, cobalt-based wear resistant alloys, such as, for example, StelliteTM. The material of coating may vary based on the temperature of operation of the combustion engine 160. For example, aluminum or aluminum alloys may be used as a coating material for the inlet valve seat 169 and inlet valve 168 of the combustion engine 160 because the temperature of operation of the inlet valve 168 is below the melting point of aluminum. However, aluminum and some low melting point aluminum alloys may not be used as the coating material for the exhaust valve seat 167 and the exhaust valve 166 because the temperature of operation of the exhaust valve 166 may be equal to or greater than the melting point of aluminum.
[0065] Incorporation of a soft, high thermal conductivity material in the coating of valves 166, 168, and valve seats 167, 169 may further enhance heat-transfer between the valves and valve seats. For example, a thermal conductivity of copper is known to be more than 20 times the thermal conductivity of a StelliteTM material. Therefore, incorporation of copper coating on the dimples of the StelliteTM base may facilitate effective transfer of heat from the combustion gases to a cooled surface of the valve seats 167, 169 through the coated surfaces of valves 166, 168 and valve seats 167, 169.
[0066] In conventional valve systems, oil lubrication is used between valve and valve seats. However, such techniques may not provide desired lubrication and wear resistance. Embodiments of the present invention disclose an exemplary friction surface coating process which enables higher lubrication, wear resistance, heat- transfer between parts, and higher operating temperatures. Further, equipment and material costs are reduced by using an exemplary friction-surfacing method, because there is no need to use expensive arcing or melting equipment. As a result, loss of the coating material is minimized.
[0067] While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.