Case hardening titanium and its alloys

Abstract

An article of titanium or a titanium-based alloy is case hardened by heat treatment at a temperate of 750° C. to 850° C. and at a pressure in the order of atmospheric pressure in a diffusion atmosphere. The diffusion atmosphere consists of a carrier gas such as argon which does not react chemically with the article in the said temperature range, and carbon monoxide. The concentration of carbon monoxide in the oxygen diffusion atmosphere is in the range of 20 volumes per million to 400 volumes per million.

1 . A method of case hardening an article of a metallic material selected from titanium, and titanium-based alloys, wherein the article is heat treated at a pressure in the range of 0.5 to 2 bar and a temperature in the range of 750° C. to 870° C. in a diffusion atmosphere, comprising (a) a carrier gas which does not react chemically with the article in the said temperature range, and (b) an active gas, wherein the concentration of the active gas in the diffusion atmosphere is in the range of 20 to 400 volumes per million, and wherein the active gas is carbon monoxide. 
   
   
       2 . The method according to  claim 1 , wherein the carbon monoxide concentration in the diffusion atmosphere is in the range of 30 to 100 volumes per million. 
   
   
       3 . The method according to  claim 1 , wherein a wear-resistant ceramic layer is formed in the heat treatment at the surface of the article. 
   
   
       4 . The method according to  claim 1 , wherein the titanium-based allow is an alloy of titanium with 4% by weight of vanadium and 6% by weight of aluminium. 
   
   
       5 . The method according to  claim 1 , wherein the duration of the heat treatment is in the range of 12 to 24 hours. 
   
   
       6 . The method according to  claim 1 , wherein the article is an engineering component. 
   
   
       7 . The method according to  claim 1 , wherein the pressure is atmospheric pressure. 
   
   
       8 . The method according to  claim 1 , wherein the carrier gas is argon. 
   
   
       9 . The method according to  claim 1 , wherein the carrier gas is selected from the group consisting of helium, neon, krypton and xeon. 
   
   
       10 . The method according to  claim 1 , wherein the diffusion atmosphere is essentially free of molecular nitrogen.