Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Reexamination Certificate
2001-08-16
2003-08-12
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
C148S210000, C148S237000, C148S279000, C427S142000
Reexamination Certificate
active
06605160
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to the repair of parts comprising metals, and surfaces and coatings of said parts using reactive metals coating processes. Coating and surface repair fall under U.S. Patent Class 427 (COATING PROCESSES), Subclass 140 (Processes directed to the restoration or repair of coatings or surfaces of objects). Surface treatments via reactive metal coating processes fall under U.S. Patent Class 148 (METAL TREATMENT), Class Definition C ( . . . processes of reactive coating of metal wherein an externally supplied carburizing or nitriding agent is combined with the metal substrate to produce a carburized or nitridized or carbonitrided coating thereon or a uniformly carburized, nitrided, or carbonitrided metal alloy containing a metal element from said substrate) and Class Definition D ( . . . processes of reactive coating of metal wherein an externally supplied agent combines with the metal substrate to produce a coating thereon which contains at least one element from said metal substrate). This invention is applicable in maintenance and restoration of parts in many industries including, but not limited to, aviation and space industries.
Coatings and Surface Treatments
Various processes are well-known for providing coatings or modified surfaces on metals to protect them from effects such as wear, erosion, and corrosion. Such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma spray, and reactive coating (boronizing, carburizing, nitridizing, carbonitridizing, etc.). For instance, U.S. Pat. No. 5,272,014 (Leyendecker) teaches a wear-resistant CVD coating for substrates such as forming or cutting tools. U.S. Pat. No. 5,656,364 (Rickerby) and U.S. Pat. No. 5,702,829 (Paidassi) teach multiple-layer erosion-resistant PVD coatings for substrates such as gas turbine engine compressor or turbine blades. U.S. Pat. No. 4,850,794 (Reynolds, Jr.) teaches solution-bath and gas nitriding to enhance the wear-resistance of steam turbine components. U.S. Pat. No. 4,588,450 (Purohit) teaches nitriding of nickel-based super alloys including inconel to improve their creep strength, fatigue strength, and resistance to oxidation. U.S. Pat. No. 6,129,988 (Vance , et al.) teaches gas nitriding of metallic bond coatings for thermal barrier coating systems. Nitriding of metallic bond coatings enhances oxidation resistance thereby prolonging the adherence of ceramic thermal barrier coatings applied thereon. CVD, PVD and plasma spray processes generally involve deposition of additional material on the surface of a substrate. Reactive coating processes generally involve incorporation or dispersion of additional chemical constituents into the existing lattice structure of a metal substrate.
Functionally Gradient Surfaces
Reactive coating processes are known for producing treated surfaces with chemical compositions that vary as a function of depth, also known as functionally gradient surfaces. For instance, surfaces produced via nitriding consist of a hard nitride layer above a nitrogen-containing diffusion zone, with nitrogen content gradually decreasing deeper into the substrate material. Richter discusses a plasma nitriding process for producing functionally gradient surfaces on stainless steel and aluminum alloys (“Nitriding of Stainless Steel and Aluminum Alloys by Plasma Immersion Ion Implantation”, Surface and Coatings Technology, Vol. 128-129, 2000, pp. 21-27). U.S. Pat. No. 4,762,756 (Bergmann) teaches a plasma nitriding process that is enhanced using arc discharge, whereby functionally gradient surfaces are produced on metals including stainless steel and titanium. Meletis discusses an enhanced plasma nitriding process for producing functionally gradient surfaces on titanium (“Characteristics of DLC Films and Duplex Plasma Nitriding/DLC Coating Treatments”, Surface and Coatings Technology, Vol. 73, 1995, pp. 39-45). This (enhanced nitriding process is also taught in expired U.S. Pat. No. 4,460,415 (Korhonen, issued Jul. 17, 1984) and U.S. Pat. No. 5,334,264 (Meletis, issued Aug. 2, 1994). U.S. Pat. No. 4,568,396 (Vardiman) teaches a carburizing method via carbon ion implantation wherein carbon content of the treated surface varies as a function of depth. PVD and CVD processes are better-known for producing coatings of uniform composition as a function of depth (monolayers), but can also be adapted to produce functionally gradient surfaces. For example, U.S. Pat. No. 5,989,397 (Laube) teaches a method and apparatus for producing deposited surfaces with depth-varying compositions of titanium, carbon, and nitrogen.
Enhanced Plasma Nitriding
A review of enhanced nitriding processes is presented by Czerwiec et al (“Low-pressure, high-density plasma nitriding: mechanisms, technology and results”, Surface and Coatings Technology, Vol. 108-109, 1998, pp. 182-190). These processes can be classified under the following four categories: Thermionically assisted d.c. triode (TAT); plasma immersion ion implantation (PIII) or plasma source ion implantation (PSII); electron cyclotron resonance (ECR) systems; and thermionic arc discharge (TAD). A version of the TAT enhanced plasma nitriding method and apparatus presented by Meletis in U.S.
Pat. No. 5,334,264 is previously taught by expired U.S. Pat. No. 4,460,415 (Korhonen), and also by earlier references including Matthews and Teer (“Characteristics of a Thermionically Assisted Triode Ion-Plating System”, Thin Solid Films, Vol. 80, 1981, pp. 41-48), Korhonen and Sirvio (“A New Low Pressure Plasma Nitriding Method”, Thin Solid Films, Vol. 96, 1982, pp. 103-108), Korhonen et al (“Plasma Nitriding and Ion Plating With an Intensified Glow Discharge”, Thin Solid Films, Vol. 107, 1983, pp. 387-394), Fancey and Matthews (“Some Fundamental Aspects of Glow Discharges in Plasma-Assisted Processes”, Surface and Coatings Technology, Vol. 33, 1987, pp. 17-29), Ahmed (“Ion Plating Technology, Develoments and Applications”, John Wiley and Sons, New York, 1987, pp. 68-70), Fancy and Matthews (“Process Effects in Ion Plating”, Vacuum, Vol. 41, No. 7-9, 1990, pp. 2196-2200), and Leyland et al (“Enhanced Plasma Nitriding at Low Pressures: A Comparative Study of D. C. and R. F. Techniques”, Surface and Coatings Technology, Vol. 41, 1990, pp. 295-304. Furthermore, Molarius et al teaches that the process of U.S. Pat. No. 4,460,415 (Korhonen) can be used to treat titanium (“Ion Nitriding of Steel and Titanium at Low Pressures”, 4th Int. Congress on Heat Treatment of Materials. Jun. 3-7, 1985. Berlin (West), Proceedings, Vol I, p. 625-643. Härterei-Technische Mitteilungen 4(1986)6, 391-398.). These references establish prior art that pre-dates the filing of the Meletis Patent by 2 to 10 years. None of these references is cited in the Meletis Patent. U.S. Pat. No. 5,334,264 therefore teaches very little that was not previously taught by prior art.
Performance of Functionally Gradient Surfaces
Functionally gradient surfaces are known to have superior wear and erosion properties compared to monolayer coatings. Voevodin presents results of scratch tests for multiple-layer titanium, titanium carbide, and diamond-like carbon (DLC) surfaces prepared using the process of U.S. Pat. No. 5,989,397 (“Design of a Ti/TiC/DLC Functionally Gradient Coating Based on Studies of Structural Transitions in Ti-C Thin Films”, Thin Solid Films, Vol. 298, 1997, pp. 107-115). Meletis presents results of wear tests for functionally gradient, nitrided titanium surfaces (“Characteristics of DLC Films and Duplex Plasma Nitriding/DLC Coating Treatments”, Surface and Coatings Technology, Vol. 73, 1995, pp. 39-45). Gachon presents results of erosion tests for functionally gradient, multiple-layer tungsten carbide coatings (“Study of Sand Particle Erosion of Magnetron Sputtered Multilayer Coatings”, Wear, Vol. 233-235, 1999, pp. 263-274). Gupta presents results showing that PVD multilayer titanium nitride coatings have superior erosion resistance compared to titanium nitride monolayer coatings on turbine engine compressor blades (“Protectiv
King Roy
Wilkins, III Harry D.
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