Wear resistant coating

Abstract

A method of forming a wear resistant and galling resistant coating for abrasive environments and a feed material for the method are disclosed. The feed material is for forming a wear resistant and galling resistant coating on a substrate by a welding process that heats the feed and the substrate. The feed material comprises 35 to 50 wt % titanium nitride particles and a balance of commercially pure titanium or titanium alloy particles and incidental impurities. The method involves delivering the feed material to a surface of a substrate and exposing the feed material and the substrate to sufficient energy to cause at least the commercially pure titanium or titanium alloy particles in the feed to melt and at least some of the titanium nitride particles in the feed to melt, thereby forming a melt pool. On solidification of the melt pool, at least some of the titanium nitride particles are embedded in a matrix formed from melt pool, thereby forming a wear resistant and galling resistant coating on the substrate. A wear resistant and galling resistant coating formed of the feed material is also disclosed.

1 . A method of forming a coating on a substrate of titanium alloy, the coating being resistant to wear and galling in a corrosive and abrasive environment, the method comprising the steps of:
 (a) delivering a feed to a surface of a substrate by conveying the feed to the substrate in an inert conveying gas and controlling the flow of the conveying gas to control the feed rate of the feed, the feed consisting of:
 (i) 35 to 50 wt % titanium nitride particles; 
 (ii) a balance of commercially pure titanium or titanium alloy particles with incidental impurities; 
   (b) heating the feed and the substrate to cause at least the commercially pure titanium or titanium alloy particles, at least some of the titanium nitride particles and at least the exposed surface of the substrate to melt to form a melt pool; and   (c) preheating the substrate and maintaining the substrate at the preheat temperature throughout steps (a) and (b); and   whereby, on solidification of the melt pool, at least some of the titanium nitride particles are embedded in a matrix formed from melt pool, thereby forming a wear resistant and galling resistant coating on the substrate.   
     
     
         2 . The method defined in  claim 1 , wherein the preheating temperature is selected to reduce or avoid cracking and porosity in the coating caused by forming excessive volumes of secondary nitrides. 
     
     
         3 . The method as defined in  claim 1 , wherein the method includes preheating the substrate before steps (a) and (b) and maintaining the substrate temperature in a range of 50° C. to 100° C. 
     
     
         4 . The method defined in  claim 1 , wherein the method includes controlling the hardness of the wear resistant coating by controlling the temperature of the molten material and the time during which the molten material remains molten. 
     
     
         5 . The method defined in  claim 1 , wherein the method includes controlling the temperature of the molten material to be between the melting temperature of titanium nitride and the vaporisation temperature of titanium. 
     
     
         6 . The method defined in  claim 1 , wherein the method includes controlling phases of titanium nitride formed upon solidification of the molten materials by controlling the time that the molten material remains molten. 
     
     
         7 . The method defined in  claim 1 , wherein step (b) involves causing localized heating of the substrate and the feed by exposing the substrate and the feed to a targeted energy source. 
     
     
         8 . The method defined in  claim 6 , wherein the heat input is controlled by adjusting (i) the intensity of the targeted energy source, (ii) the duration of exposure to the targeted energy source and (iii) the area of substrate exposed to the targeted energy source. 
     
     
         9 . A titanium alloy autoclave or valve component having a coating that is resistant to wear and galling in a corrosive and abrasive environment, the wear and galling resistant coating comprises 35 to 50 wt % of titanium nitride particles dispersed in a matrix of commercially pure titanium or titanium alloy. 
     
     
         10 . A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in  claim 9 , wherein the titanium nitride particles comprise 35 to 45 wt % of the wear resistant coating. 
     
     
         11 . A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in  claim 9 , wherein the titanium nitride particles comprise 35 to 42 wt % of the wear resistant coating. 
     
     
         12 . A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in  claim 9 , wherein the matrix of titanium or titanium alloy comprises alloying elements with the balance being at least 50 wt % titanium and incidental impurities. 
     
     
         13 . A titanium alloy autoclave or valve component having a wear resistant and galling resistant coating as defined in  claims 9 , wherein the wear resistant coating is formed to a thickness of greater than 0 and up to 10 mm.