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U.S. Patent May 15,2007 Sheet 1 of 2 US 7,216,661 B2
U.S. Patent May 15,2007 Sheet 2 of 2 US 7,216,661 B2
METHOD OF FORMING A WEAR
CROSS-REFERENCE TO RELATED
This application is a continuation of U.S. patent application Ser. No. 10/741,848 filed Dec. 18, 2003 now U.S. Pat. No. 6,935,618, which is a continuation of U.S. patent application Ser. No. 10/322,871, filed Dec. 18, 2002 now 10 U.S. Pat. No. 6,094,935, both of which are incorporated herein by reference in their entirety.
This invention relates generally to multi-layer surface coatings for use with articles of manufacture and products requiring low friction, low wear, and protective exterior surfaces. More particularly, the invention is related to articles having mutually sliding components, such as valve 20 components for water mixing valves, having surface protective layers comprising a strengthening layer and an outer amorphous diamond coating.
In certain applications, such as for example, valve plates for fluid control valves, there is a need for mutually sliding 25 surfaces to be wear resistant, abrasion resistant, scratch resistant, and to have a low coefficient of friction. The elements of one type of control valve for mixing of hot and cold water streams typically comprise a stationary disk and a moveable sliding disk, although the plate elements may be 30 of any shape or geometry having a sealing surface, including e.g. flat, spherical, and cylindrical surfaces. The term "disk" herein therefore refers to valve plates of any shape and geometry having mating surfaces which engage and slide against each other to form a fluid-tight seal. The stationary 35 disk typically has a hot water inlet, a cold water inlet, and a mixed water discharge outlet, while the moveable disk contains similar features and a mixing chamber. It is to be understood that the mixing chamber need not be in the disk but could part of an adjacent structure. The moveable disk 40 overlaps the stationary disk and may be slid and/or rotated on the stationary disk so that mixed water at a desired temperature and flowrate is obtained in the mixing chamber by regulating the flowrate and proportions of hot water and cold water admitted from the hot water inlet and the cold 45 water inlet and discharged through the mixed water discharge outlet. The disks mating sealing surfaces should be fabricated with sufficient precision to allow the two sealing surfaces to mate together and form a fluid tight seal (i.e. they must be co-conformal and smooth enough to prevent fluid 50 from passing between the sealing surfaces). The degree of flatness (for a flat plate shape), or co-conformity (for non-flat surfaces) and smoothness required depend somewhat on the valve construction and fluids involved, and are generally well known in the industry. Other types of disk valves, while 55 still using mating sealing surfaces in sliding contact with each other, may control only one fluid stream or may provide mixing by means of a different structure or port configuration. The stationary disk may for example be an integral part of the valve body. 60
Previous experience with this type of control valve has demonstrated there is a problem of wear of the mating surfaces of the disks due to the fact that the stationary and moveable disks are in contact and slide against each other (see for example U.S. Pat. Nos. 4,935,313 and 4,966,789). 65 In order to minimize the wear problem, these valve disks are usually made of a sintered ceramic such as alumina (alumi
num oxide). While alumina disks have good wear resistance, they have undesirable frictional characteristics in that operating force increases, and they tend to become "sticky" after the lubricant grease originally applied to the disks wears and washes away. The scratch and abrasion resistance of alumina plates to large and small particles (respectively) in the water stream is good; however, they are still susceptible to damage from contaminated water streams containing abrasive particles such as sand; and improvement in this regard would be beneficial. Additionally, the porous nature of the sintered ceramic disks makes them prone to "lockup" during long periods of non-use, due to minerals dissolved in the water supply that precipitate and crystallize between coincident pores in the mating surfaces. One objective of the present invention is to provide disks having reduced wear, improved scratch and abrasion resistance and reduced frictional characteristics. Another objective is to provide non-porous or reduced-porosity valve disks to reduce the number of locations where precipitated crystals may form between the mating surfaces.
Sintered ceramics in particular are relatively difficult and expensive (due to their hardness) to grind and polish to a degree of co-conformity and smoothness adequate for sealing. It would be advantageous to use a material for the disks, such as metal, which is less expensive, easier to grind and polish and which is not porous. However, the wear resistance and frictional behavior of bare metallic disks is generally not acceptable for sliding seal applications. A further objective of the present invention is to provide disks made of metal a base material and having improved wear, scratch, and abrasion resistance and improved frictional characteristics as compared to uncoated ceramic disks.
It is disclosed in the prior art (e.g. U.S. Pat. Nos. 4,707, 384 and 4,734,339, which are incorporated herein by reference) that polycrystalline diamond coatings deposited by chemical vapor deposition (CVD) at substrate temperatures around 800-1000 C can be used in combination with adhesion layers of various materials in order to provide scratch and wear resistant components. Polycrystalline diamond films, however, are known to have rough surfaces due to the crystal facets of the individual diamond grains, as is apparent in the photographs of FIGS. 2 and 3 in the '384 patent. It is known in the art to polish such surfaces in order to minimize the coefficient of friction in sliding applications, or even to deposit the polycrystalline diamond on a smooth substrate and then remove the film from the substrate and use the smooth side of the film (which was previously against the substrate) rather than the original surface as the bearing surface. The present invention overcomes prior art problems by providing a number of advantageous features, including without limitation providing a smooth and very hard surface for sliding applications, while avoiding difficult and expensive post-processing of a polycrystalline diamond surface layer. The methodology also advantageously employs substrate materials (such as, suitable metals, glasses, and composite and organic materials) that cannot be processed at the elevated temperatures necessary for CVD deposition of polycrystalline diamond.
It is also disclosed in the prior art (e.g. U.S. Pat. No. 6,165,616, which is incorporated herein by reference) that engineered interface layers may be employed to relieve thermally-induced stress in a polycrystalline diamond layer. These thermally induced stresses arise during cooling of the substrate after coating deposition at relatively high temperatures, and are due to the difference in thermal expansion coefficient between the substrate and the diamond coating. Rather complicated engineering calculations are specified in
'616 to predetermine the desired interface layer composition and thickness. The interface layer thickness' disclosed in '616 to minimize the thermally-induced stress in the diamond layer are of the order 20 to 25 microns according to FIGS. 1 through 3. Such thick interface layers are expensive 5 to deposit, due to the time necessary to deposit them and the high cost of the equipment required. The present invention also advantageously includes, without limitation, minimizing the coating cost but still achieving desired results by employing much thinner interface layers than those taught 10 by '616, and to avoid creating the thermally-induced stresses which necessitate such complicated engineering calculations by depositing a hard surface layer at a relatively low temperature compared to the prior art, such as the '616 patent. 15
It is further disclosed in the prior art (e.g. U.S. Pat. Nos. 4,935,313 and 4,966,789, which are incorporated herein by reference) that cubic crystallographic lattice carbon (polycrystalline diamond) and other hard materials may be used as surface coatings on valve disks, and that pairs of mutually 20 sliding valves discs which differ from each other in either surface composition or surface finish are preferable to those which are the same in these characteristics, with respect to minimizing friction between the plates. The present invention provides mating valve disk surfaces having a lower 25 friction coefficient than the disclosed materials in waterlubricated or fluid wetted surface applications such as water valves, and to allow identical processing of both mating surfaces in order to avoid the need to purchase and operate different types of processing equipment. The present inven- 30 tion further provides, without limitation, mating valve disk surfaces having a lower friction coefficient than the disclosed materials in water-lubricated or fluid wetted surface applications such as water valves. Furthermore, both mated sliding surfaces of the disks can be hard and have an 35 abrasion resistance to contaminated water streams and to allow identical processing of both mating surfaces in order to avoid the need to purchase and operate different types of processing equipment.
An exemplary embodiment relates to a method of forming a wear resistant component that includes providing a base material, depositing a strengthening layer on the base mate- 45 rial, and vapor depositing an amorphous diamond layer on the strengthening layer.
Another exemplary embodiment relates to a method of producing a valve plate that includes providing a strengthening layer on a substrate and providing amorphous dia- 50 mond on the strengthening layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is one form of valve incorporating a multi-layer 55 structure with an amorphous diamond layer overlying a substrate;
FIG. 2 is a detail of one form of multi-layer structure of the invention;
FIG. 3 illustrates yet another multi-layer structure with an 60 added additional adhesion-promoting layer;
FIG. 4 is a further form of multi-layer structure of FIG. 2 wherein a strengthening layer includes two layers of different materials; and
FIG. 5 is a photomicrograph of the surface appearance of 65 an exterior amorphous diamond layer over an underlying substrate or layer.
DESCRIPTION OF THE PREFERRED
Embodiments of the invention are illustrated generally in the figures, where FIG. 1 shows one form of the valve 10 with handle 12 incorporating the invention. In particular, FIGS. 2-4 illustrate a portion of a valve 10 having a substrate 18 for a sliding component 20 and/or a fixed component 22 of the valve 10 which can comprise a base material wherein the base material can be the same or different in the sliding component 20 and the fixed component 22. In other embodiments, one of the components 20, 22 can be fixed. Preferably the base material is a sintered ceramic or a metal. Base materials can also comprise glasses or glassy materials, cermets, polymeric materials, composite materials, intermetallic compounds such as iron aluminide, and other materials mechanically suitable for the application. The metals can include, for example, any conventional metal, including without limitation, stainless steel, brass, zirconium, titanium, aluminum, and alloys of the latter three materials. Stainless steel, titanium, and zirconium, and aluminum are the most preferred metals, with the term stainless steel referring to any type such as 304, 316, etc., and customized variations thereof and with the terms titanium, zirconium, and aluminum understood to include alloys comprised mostly of those metals. Sintered (powdered) stainless steel is a preferred substrate material because it can be economically molded into complex shapes suitable for disks and can be economically ground and polished to achieve a mating smooth sealing surface. In the case of sintered stainless steel, "fully dense" substrates and metal injection molded substrates are preferred. Titanium and zirconium are preferred base materials because they can be easily oxidized or anodized to form a hard surface layer. Ceramics can be any conventional ceramic material, including without limitation, for example, sintered alumina (aluminum oxide) and silicon carbide, with alumina being a preferred material. Composite materials can include, for example, any conventional cermets, fiber reinforced epoxies and polyamides, and carbon-carbon composites. Glass and glassy materials can include for example borosilicate glass such as PyrexTM, and materials such as toughened laminated glass and glassceramics. Glass, glassy materials and cermets are preferred substrates because they can be economically molded into complex shapes suitable for disks and can be economically ground and polished to a flat and smooth surface. Iron aluminide is understood to be a material consisting mainly of that iron and aluminum but may also contain small amounts of such other elements as molybdenum, zirconium, and boron.
As shown in FIG. 2, a strengthening layer 23 can also be placed directly on the substrate surface 18. This layer 23 can comprise a material having higher hardness than the substrate 18. Suitable materials for the strengthening layer 23 can include compounds of Cr, Ti, W, Zr, and any other metals conventionally known for use in hard coatings. The compounds include without limitation are nitrides, carbides, oxides, carbo-nitrides, and other mixed-phase materials incorporating nitrogen, oxygen, and carbon. One highly preferred material for the strengthening layer 23 is chromium nitride. Chromium nitride in the present application most preferably refers to a single or mixed phase compound of chromium and nitrogen having nitrogen content in the range of about 10 to about 50 atomic percent. The term chromium nitride also refers to a material containing such doping or alloying elements as yttrium, scandium, and lanthanum in addition to chromium and nitrogen.
Another material suitable for the strengthening layer 23 is conventional DLC (Diamond-Like Carbon), which is a form of non-crystalline carbon well known in the art and distinct from amorphous diamond. DLC coatings are described for example in U.S. Pat. No. 6,165,616 (in which they are called 5 (a-C) coatings). DLC can be deposited by sputtering or by conventional CVD. DLC is an amorphous material with mostly sp2 carbon bonding and little of the tetrahedral sp3 bonding that characterizes amorphous diamond. The hardness of DLC is substantially lower than that of amorphous 10 diamond and is more similar to the hardness of conventional hard coating materials such as titanium nitride and chromium nitride. The internal stresses in DLC coatings are also lower than those in amorphous diamond coatings, allowing DLC to be deposited in thicker layers than amorphous 15 diamond without loss of adhesion. The term DLC as used herein includes hydrogenated forms of the material.
The strengthening layer 23 functions primarily to improve scratch and abrasion resistance of the multilayer coating. 2Q The hardness of the strengthening layer 23 should be at least greater than that of the substrate 18 in order to perform its intended function of improving the scratch resistance of the coated disk. The thickness of the strengthening layer 23 is at least a thickness sufficient to improve the scratch resistance 25 of the substrate 18. For materials typically used as hard coatings, such as those disclosed above, this thickness is generally from around 500 nm to around 10 microns, and preferably from about 2000 nm to around 5000 nm. In testing of faucet water valves it has been found that a 3Q chromium nitride strengthening layer having a thickness of about 5 microns provides adequate scratch and abrasion resistance (in conjunction with a thin amorphous diamond top layer) for types and sizes of contaminants considered to be typical in municipal and well water sources. 35
In some embodiments of the present invention as shown in FIG. 3 and for component 22 of FIG. 4, a thin adhesionpromoting layer 21 can be deposited on the substrate 18 and then the strengthening layer 23 on the layer 21. This layer 21 functions to improve the adhesion of the overlying strength- 40 ening layer 23 to the substrate 18. Suitable materials for the adhesion-promoting layer 21 include preferably chromium and also can include titanium, tungsten, other refractory metals, silicon, and other materials known in the art to be suitable as adhesion-promoting layers. The layer 21 can 45 conveniently be made using the same elemental material chosen for the strengthening layer 23. The layer 21 has a thickness that is at least adequate to promote or improve the adhesion of layer 23 to the substrate 18. This thickness is generally from about 5 nm to about 200 nm, and most 50 preferably from about 30 nm to about 60 nm. The adhesionpromoting layer 21 can be deposited by conventional vapor deposition techniques, including preferably physical vapor deposition (PVD) and also can be done by chemical vapor deposition (CVD). 55
PVD processes are well known and conventional and include cathodic arc evaporation (CAE), sputtering, and other conventional deposition processes. CVD processes can include low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), and 60 thermal decomposition methods. PVD and CVD techniques and equipment are disclosed, inter alia, in J. Vossen and W. Kern "Thin Film Processes II", Academic Press, 1991; R. Boxman et al, "Handbook of Vacuum Arc Science and Technology", Noyes, 1995; and U.S. Pat. Nos. 4,162,954 65 and 4,591,418, with the patents incorporated herein by reference.
In the case of sintered ceramic materials, although the individual granules forming the sintered material may have high hardness, the scratch resistance of the overall sintered structure as measured by scratch testing is much lower than that of the material forming the granules (e.g. alumina). This is due to the fact that the materials typically used to sinter or bond the alumina granules together, typically silicates, are not as hard as the granules themselves. The hardness of the strengthening layer 23 can be similar to or even less than the hardness of the individual granules comprising the ceramic disk, and still being harder than the overall sintered ceramic structure. It has been found by experiment, for example, that the depth of the scratch caused by a stylus (radius=100 microns) sliding under a load of 30 Newtons is approximately 4-6 microns on an uncoated sintered alumina substrate, while the scratch depth on an identical substrate coated with a 3 micron thick chromium nitride strengthening layer is only 2-3 microns.
The strengthening layer 23 can be formed by conventional vapor deposition techniques including, but not limited to sputtering, cathodic arc evaporation (CAE), and CVD. The most preferred methods are sputtering, CAE, or other means which may be carried out at a relatively low temperature, thereby minimizing thermally-induced stresses in the coating stack upon cooling. If the strengthening layer 23 is deposited by CAE, it is also desirable to use macroparaticle filtering in order to control and to preserve the smoothness of the surface of the substrate 18. The strengthening layer 23 can also be formed by other well-known methods for forming hard coatings such as spray pyrolysis, sol-gel techniques, liquid-dipping with subsequent thermal treatment, nano-fabrication methods, atomic-layer deposition methods, and molecular-layer deposition methods.
The strengthening layer 23 can alternatively be formed by a process that produces a hardened surface layer on the substrate base material. Such processes include, for example, thermal oxidation, plasma nitriding, ion implantation, chemical and electrochemical surface treatments such as chemical conversion coatings, anodizing including hard anodizing and conventional post-treatments, micro-arc oxidation and case hardening. The strengthening layer 23 can also include multiple layers 24 and 25 as shown in FIG. 4, in which the layers 24 and 25 together form the strengthening layer 23. For example, the layer 24 can be an oxide thermally grown on the substrate base material while the layer 25 is a deposited material such as CrN. The strengthening layer 23 can also include more than two layers, and can preferably comprise for example a superlattice type of coating with a large number of very thin alternating layers. Such a multilayer or superlattice form of the strengthening layer 23 can also include one or multiple layers of amorphous diamond.
In the multi-layer structure of FIGS. 1-4 the amorphous diamond layer 30 is deposited over the strengthening layer 23 to form an exterior surface layer. The purpose of the amorphous diamond layer 30 is to provide a very hard wear abrasion resistant and lubricous top surface on the sliding components. Amorphous diamond is a form of non-crystalline carbon that is well known in the art, and is also sometimes referred to as tetrahedrally-bonded amorphous carbon (taC). It can be characterized as having at least 40 percent sp3 carbon bonding; a hardness of at least 45 gigaPascals and an elastic modulus of at least 400 gigaPascals. Amorphous diamond materials are described in U.S. Pat. Nos. 5,799,549 and 5,992,268, both of which are incorporated herein by reference. The amorphous diamond material layer 30 can be applied processes including, for