Nitriding Method for Improving Surface Characteristics of Cobalt-Chromium Based Alloys
Inactive Publication Date: 2008-01-03
PATROVSKY HUBERT
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- Application Information
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Benefits of technology
[0019] A still further aspect of the present invention is a process as aforesaid wherein the compound layer provides a hard surface with improved wear resistance.
[0030] The method of the present invention achieves a harder and smoother surface without significant change to the metallurgical properties of the base metal cobalt-chromium alloy. An additional merit of the current invention is the surface conversion of load bearing surfaces while maintaining the equivalent metallurgical properties including, but not limited to, fatigue strength.
Problems solved by technology
A particular limitation of cobalt chrome based alloys is that the metal morphology can lend itself to the formation of carbides at the finished surface of the metal.
Conditions of articulating or sliding motion or relative motion of opposing abutting surfaces, where one of the surfaces is composed of a cobalt-chromium alloy as aforesaid, with another surface which may be made of the same or different material, will result in undesirable wear conditions on the mating surface due to the hard particles or discontinuities on the opposing surface.
This may give rise to undesirable results, associated not only with the damage to the opposing surface, but also to the generation of particles arising from the damaged surface.
Such generated damage particles may be undesirable in many circumstances for example, bearing components that are composed of a cobalt-chromium metal alloy.
However, such processes can lead to a significant increase in the nitrogen content present throughout the bulk alloy metal.
Such processing may also lead to hydrogen embrittlement and decarburization due to the presence of free hydrogen from the dissociated ammonia in the process.
According to the disclosed process, there is prevention or minimizing of the formation of a chromium nitride compound layer on the surface due to apparent detrimental effects therein associated with purported increase in surface roughness and brittleness which lead to reduced wear resistance and a reduction of fatigue strength.
Ion implantation is a line of site process, therefore making uniformity of treatment extremely difficult if not impossible to achieve on complex geometries.
Salt bath nitriding exposes the parts to excessive temperatures and gas nitriding causes hydrogen embrittlement and decarburization near the surface.
Method used
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[0035] The present invention relates to a method for enhancing the surface hardness and smoothness of a cobalt-chromium alloy, as well as wear resistance, while maintaining consistent metallurgical properties for the base metal. The method of the present invention imparts improved wear resistance properties. The present invention also comprises a component fabricated from cobalt-chromium based alloys with a compound surface layer. The process of the present invention allows control of the transition layer and a component or part of the present invention may also comprise such a transition layer, below the surface layer. The product or component also comprises a substrate metal of cobalt-chromium alloy.
[0036] The component is conditioned by hardening the surface of the cobalt-chromium base alloy metal by exposing all or part of a surface of a component or product made of such an alloy to a reaction gas, including nitrogen, at a pressure of less than 1 atmosphere and at a process tem...
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Abstract
A method for improving the surface characteristics of Cobalt chromium alloys by plasma nitriding. By creating a glow discharge around the parts with selective gases at partial pressures a compound layer is formed at the surface beneficial for wear applications. A further benefit is an increase in the load bearing capacity of the surface as compared to standard material.
Description
FIELD OF INVENTION [0001] The present invention relates to cobalt-chromium based alloys and particularly to a method of surface treatment of such alloys, beneficial for surface hardness, smoothness and corrosion and wear resistance, while meeting the criteria of at least equivalent fatigue strength. BACKGROUND [0002] Cobalt-chromium based alloys, including cobalt-chromium molybdenum alloys are known in the art and the properties of such alloys make them suitable for selection in many specialized types of applications, requiring heat resistance, high surface hardness, wear resistance, high surface smoothness, mechanical strength, resistance to surface degradation and biocompatibility. [0003] Many applications will be known for such alloys, a non-exhaustive list including aircraft and steam turbines, stationary gas turbines, reciprocating engines, metal processing, medical applications and devices, space vehicles, heat treatment equipment, nuclear power systems, chemical and petrochem...
Claims
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Login to View More IPC IPC(8): C23C8/24C23C8/20C23C8/36C23C26/00
CPCC23C8/20C23C26/00C23C8/36C23C8/24
InventorPATROVSKY, HUBERT
OwnerPATROVSKY HUBERT