Abstract: A method of modifying a surface characteristic of a stainless steel or cobalt-chromium (Co—Cr) based alloy article, comprising plasma surface co-alloying the article (such as by active screen plasma surface co-alloying), with both interstitial and substitutional alloying elements at a temperature in the range of from 300 to 600° C. and at a pressure of from 100 to 1500 Pa for 1 to 50 hours in an atmosphere comprising N-containing, C-containing or N/C-containing gas.

Abstract: The present invention relates to a method of modifying a surface characteristic (e.g., wear resistance and/or corrosion resistance) of a cobalt-chromium based alloy article. The method comprises plasma treating the article at a temperature in the range of from 300° C. to 700° C. and at a pressure of from 100 Pa to 1500 Pa for 1 hour to 50 hours in an atmosphere comprising at least one carbon-containing gas, whereby to introduce carbon into a surface region of said article. The present invention also resides in a surface-hardened cobalt-chromium based article producible by the method of the invention. The article is characterised by having a surface region comprising a supersaturated solid solution of carbon in cobalt or a surface region comprising a supersaturated solid solution of carbon in cobalt and chromium carbides. Surface hardened articles producible by the method of the invention include medical implants and engineering components.

Abstract: The present invention relates to a method of modifying a surface characteristic (eg. wear resistance and/or corrosion resistance) of a cobalt-chromium based alloy article. The method comprises plasma treating the article at a temperature in the range of from 300 to 700° C. and at a pressure of from 100 to 1500 Pa for 1 to 50 hours in an atmosphere comprising at least one carbon-containing gas, whereby to introduce carbon into a surface region of said article. The present invention also resides in a surface-hardened cobalt-chromium based article producible by the method of the invention. The article is characterised by having a surface region comprising a supersaturated solid solution of carbon in cobalt or a surface region comprising a supersaturated solid solution of carbon in cobalt and chromium carbides. Surface hardened articles producible by the method of the invention include medical implants and engineering components.

Abstract: A method of case hardening an article formed of titanium, zirconium or an alloy of titanium and/or zirconium is disclosed. First, the article is heat-treated in an oxidizing atmosphere at a temperature in the range of 700 to 1000° C. so as to form an oxide layer on the article. Then, the article is further heat-treated in a vacuum or in a neutral or inert atmosphere at a temperature in the range of 700 to 1000° C. so as to cause oxygen from the oxide layer to diffuse into the article.

Abstract: The tribological behavior of titanium or titanium alloy article is improved by gaseous oxidation of the article at a temperature in the range of 500 to 725° C. for 0.5 to 100 hours, the temperature and time being selected such as to produce an adherent surface compound layer containing at least 50% by weight of oxides of titanium having a rutile structure and a thickness of 0.2 to 2 &mgr;m on a solid solution-strengthened diffusion zone wherein the diffusing element is oxygen and the diffusion zone has a depth of 5 to 50 &mgr;m.

Abstract: A titanium alloy product having good tribological properties without the need to introduce an alloying element into the surface is produced by casting or casting and forging a titanium alloy consisting of 2 to 15% by weight silicon or 5 to 15% by weight nickel, 0 to 7% by weight of at least one strengthening element selected from aluminum, tin, zirconium, chromium, manganese, iron, molybdenum and niobium, and 0 to 2% by weight of a surface improving alloying element selected from boron, carbon, nitrogen, oxygen, and zirconium, the balance apart from impurities and incidental ingredients being titanium. Such alloy is then surface treated by surface melting and rapid solidification so as to produce a hard, wear-resistant surface layer without substantially affecting the bulk properties of the alloy.