Method of forming rigid layer on titanium and titanium alloy having rigid layer formed by the same

Abstract

Disclosed is a method capable of inexpensively forming a gradient-hardened rigid layer which has characteristics of functionally graded material on the surface layer of titanium. The method includes (a) injecting titanium into a heat treatment apparatus and performing ventilation to maintain an atmospheric pressure of 10 −4 torr or less, (b) performing a pretreatment process of heating the titanium at 730 to 800° C. for 10 minutes to 5 hours to remove an oxide film formed on the surface of the titanium, (c) injecting one or more gases selected from nitrogen, oxygen, and carbon into the heat treatment apparatus and heating the titanium at 740 to 950° C. for 30 minutes to 20 hours such that a gradient-hardened rigid layer having a concentration gradient of the gases is formed on the surface of the titanium, and (d) cooling the titanium.

1 . A method of forming a gradient-hardened rigid layer on a surface of titanium, the method comprising the steps of:
 (a) injecting titanium into a heat treatment apparatus and performing ventilation to maintain an atmospheric pressure of 10 −4  torr or less;   (b) performing a pretreatment process of heating the titanium at 730 to 800° C. for 10 minutes to 5 hours to remove an oxide film formed on the surface of the titanium;   (c) injecting one or more gases selected from nitrogen, oxygen, and carbon into the heat treatment apparatus and heating the titanium at 740 to 950° C. for 30 minutes to 20 hours such that a gradient-hardened layer having a concentration gradient of the gases is formed on the surface of the titanium; and   (d) cooling the titanium.   
     
     
         2 . The method of  claim 1 , wherein the atmospheric pressure of the step (a) is 5×10 −5  torr or less. 
     
     
         3 . The method of  claim 1 , wherein the step (b) is performed for 10 minutes to 1 hour. 
     
     
         4 . The method of  claim 1 , wherein a temperature in the step (c) is higher than that in the step (b). 
     
     
         5 . The method of  claim 1 , wherein the step (c) is performed at 740 to 850° C. 
     
     
         6 . The method of  claim 1 , wherein the cooling of the titanium in the step (d) comprises a step cooling method. 
     
     
         7 . The method of  claim 1 , wherein the step (d) comprises an aging step of maintaining titanium at 500 to 800° C. for 30 minutes to 30 hours. 
     
     
         8 . The method of  claim 1 , further comprising after the step (d), a step of forming one or more coating layers using over-layer coating methods such as a CVD method and a PVD method. 
     
     
         9 . The method of  claim 1 , wherein in step (c) the gases are a mixture gas of oxygen and nitrogen, or a mixture gas of carbon and nitrogen. 
     
     
         10 . The method of  claim 1 , wherein the titanium is pure titanium or a titanium alloy. 
     
     
         11 . Titanium having a gradient-hardened rigid layer formed by the method of  claim 1 . 
     
     
         12 . A titanium part having a rigid layer formed by the method of  claim 1 .