Patent Application
20180298496
The following description relates to corrosion and fatigue resistant coatings and, more particularly, to corrosion and fatigue resistant coatings for a non-line-of-sight (NLOS) process.
Hard coatings are often used to impart wear resistance to a substrate in a variety of applications. These include, for example, automotive cylinders, hydraulic actuators, aircraft landing gear and precision valves. The coatings provide a level of protection from the operating environment which would otherwise lead to abrasive, adhesive or erosive wear. The coatings may be used with a variety of substrate materials such as stainless steels, carbon steels, titanium alloys, nickel based superalloys, aluminum alloys or magnesium alloys.
In cases where abrasive wear is a major concern, the coatings serve to defeat damage that would be caused by entrained particulate matter. The coatings do this by, among other things, providing resistance to penetration cutting damage when particles are captured between contacting surfaces. In erosive wear cases, the coatings resist penetration and damage to the substrate and, in some cases, can fracture the impinging particulate. In adhesive wear cases, the coatings can serve to lower the coefficient of friction of a counterface, for instance, in a metal-to-metal contact situation where material couples would otherwise be metallurgically compatible and have a propensity to adhere to one another under contact stress.
According to one aspect of the disclosure, a non-line-of-sight (NLOS) coating process is provided for a substrate having first and second transverse surfaces where the second surface lacks a LOS for depositional processing. The NLOS coating process includes electroplating or electroless plating a crack-resistant interlayer coating to at least the second surface and applying a wear-resistant coating to the crack-resistant interlayer coating by electrolytic or electroless plating.
In accordance with additional or alternative embodiments, the substrate defines a bore-hole and the second surface is an interior facing surface of the bore-hole.
In accordance with additional or alternative embodiments, the substrate includes at least one or more of stainless steels, carbon steels, titanium alloys, nickel based superalloys, aluminum alloys and magnesium alloys and the crack-resistant interlayer coating has a low elastic modulus and/or a high fracture toughness as compared to the substrate.
In accordance with additional or alternative embodiments, the crack-resistant interlayer coating is porous.
In accordance with additional or alternative embodiments, the crack-resistant interlayer coating includes at least one of zinc (Zn), tin (Sn), tin-zinc (Sn—Zn), silver (Ag), indium (In), bismuth (Bi), gold (Au), lead (Pb), cadmium (Cd) and aluminum (Al).
In accordance with additional or alternative embodiments, the electrolytic or electroless plating includes nickel plating.
In accordance with additional or alternative embodiments, the wear-resistant coating includes at least one of chromium (Cr), cobalt phosphorus (Co—P), nickel tungsten (Ni—W), ni (Ni), cobalt (Co), nickel cobalt (Ni—Co), nickel boron (Ni—B) and nickel phosphorus (Ni—P).
In accordance with additional or alternative embodiments, the wear-resistant coating further includes boron nitride (BN) or cubic BN, diamonds, chromium carbide (Cr3C2) and silicon carbide (SiC).
In accordance with additional or alternative embodiments, the NLOS coating process further includes at least one of interposing a corrosion-resistant coating between the substrate and the crack-resistant interlayer coating and interposing the corrosion-resistant coating between the crack-resistant interlayer coating and the wear-resistant coating.
In accordance with additional or alternative embodiments, where the corrosion-resistant coating is interposed between the substrate and the crack-resistant interlayer coating, the corrosion resistant coating comprises at least one of zinc (Zn), tin (Sn) and tin-zinc (Zn—Sn), and, where the corrosion-resistant coating is interposed between the crack-resistant interlayer coating and the wear-resistant coating, the corrosion-resistant coating comprises at least one of nickel phosphorous (Ni—P), nickel (Ni), Zn, Sn, Sn—Zn and zinc nickel (Zn—Ni).
According to another aspect of the disclosure, a non-line-of-sight (NLOS) coating process is provided. The NLOS coating process includes providing a substrate having first and second transverse surfaces, the second surface lacking a LOS for depositional processing, electroplating or electroless plating a crack-resistant interlayer coating having first and second opposite interfaces proximate to at least the second surface such that the first interface faces the second surface, applying a wear-resistant coating to the second interface of the crack-resistant interlayer coating by electrolytic or electroless plating and at least one of interposing a corrosion-resistant coating between the second surface and the first interface of the crack-resistant interlayer coating and interposing the corrosion-resistant coating between the crack-resistant interlayer coating and the wear-resistant coating.
According to another aspect of the disclosure, a coated article is provided. The coated article includes a substrate having first and second transverse surfaces, the second surface lacking a LOS for depositional processing, a crack-resistant interlayer coating which is electroplated or electroless plated to at least the second surface and a wear-resistant coating which is electrolyticly or electrolessly plated to the crack-resistant interlayer coating.
In accordance with additional or alternative embodiments, the substrate defines a bore-hole and the second surface is an interior facing surface of the bore-hole.
In accordance with additional or alternative embodiments, the substrate includes at least one or more of stainless steels, carbon steels, titanium alloys, nickel based superalloys, aluminum alloys and magnesium alloys and the crack-resistant interlayer coating has a low elastic modulus and/or a high fracture toughness as compared to the substrate.
In accordance with additional or alternative embodiments, the crack-resistant interlayer coating is porous.
In accordance with additional or alternative embodiments, the crack-resistant interlayer coating includes at least one of zinc (Zn), tin (Sn), tin-zinc (Sn—Zn), silver (Ag), indium (In), bismuth (Bi), gold (Au), lead (Pb), cadmium (Cd) and aluminum (Al).
In accordance with additional or alternative embodiments, the wear-resistant coating includes at least one of chromium (Cr), cobalt phosphorus (Co—P), nickel tungsten (Ni—W), ni (Ni), cobalt (Co), nickel cobalt (Ni—Co), nickel boron (Ni—B) and nickel phosphorus (Ni—P).
In accordance with additional or alternative embodiments, the wear-resistant coating further includes boron nitride (BN) or cubic BN, diamonds, chromium carbide (Cr3C2) and silicon carbide (SiC).
In accordance with additional or alternative embodiments, the coated article further includes at least one of interposing a corrosion-resistant coating between the substrate and the crack-resistant interlayer coating and interposing the corrosion-resistant coating between the crack-resistant interlayer coating and the wear-resistant coating.
In accordance with additional or alternative embodiments, where the corrosion-resistant coating is interposed between the substrate and the crack-resistant interlayer coating, the corrosion resistant coating comprises at least one of zinc (Zn), tin (Sn) and tin-zinc (Zn—Sn), and, where the corrosion-resistant coating is interposed between the crack-resistant interlayer coating and the wear-resistant coating, the corrosion-resistant coating comprises at least one of nickel phosphorous (Ni—P), nickel (Ni), Zn, Sn, Sn—Zn and zinc nickel (Zn—Ni).
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
Major considerations in the application of coatings in certain applications include, but are not limited to, corrosion and fatigue concerns. That is, coatings must possess requisite corrosion resistance for the applications in which they are employed. In addition, an ideal coating would often be galvanically similar to the material of the substrate on which the coating is applied. This mitigates the potential for enhanced corrosion cells in the event of a partial loss or pitting of the coating. An ideal coating would also not adversely affect the expected fatigue life of the substrate being protected and in fact certain coatings, if they are well-adhered to the underlying substrate, can have a deleterious effect on fatigue life. For instance, a hard chromium coating (which is a widely used wear-resistant coating) on an aluminum substrate can degrade the life of the component due to the formation of cracks in the chromium. Such intrinsic cracking can then provide sites for fatigue crack propagation into and through the aluminum at a lower effective threshold than what would be present for uncoated aluminum. In such cases, the chromium coating not only reduces the life of the component but also may not even provide adequate corrosion resistance.
A situation where a hard coating actually increases cracking rates and propagation can be addressed by the provision of an interlayer coating that resists crack growth. An example of such a coating is taught in U.S. Pat. No. 7,854,966 which describes an interlayer coating having an elastic modulus which is lower than the substrate being protected and a top coating of cemented carbide material. While this coating addresses the problem of crack growth, the top coating is deposited via line-of-sight (LOS) processes and may be less effective or impossible to apply in non-line-of-sight (NLOS) cases.
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As a general matter, a LOS process could be defined as having an inherent LOS limitation where coating properties are significantly degraded beyond a certain deposition angle. Here, it is to be understood that LOS limitations vary by process such that a LOS process for certain deposition angles is a NLOS process for other deposition angles or two different processes can be regarded as LOS and NLOS processes, respectively, for a given deposition angle.
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In accordance with embodiments, the bore-hole 303 may have a length to diameter (L/D) ratio of greater than 2 or, more particularly, greater than 2.75. Thus, it is to be understood that LOS processes could not be easily or reliably employed to form a coating along an entirety of the second surface 302.
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As used herein, the term “electroplating” refers to a process that uses electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode or, in this case, at least the second surface 302 of the substrate 300. Electroplating or electrodeposition is primarily used to change the surface properties of an object but may also be used to build up surface thicknesses or to form objects by electroforming. As used herein, the term “electroless plating,” which is also known as chemical or auto-catalytic plating, is a non-galvanic plating method that involves several simultaneous chemical reactions in an aqueous solution, which occur without the use of external electrical power. A main difference between electroless plating and electroplating arises from the fact that electroless plating does not use external electrical power.
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While the disclosure is provided 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 the exemplary embodiment(s) may include only some of the described exemplary aspects. 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.
