Oxidation resistant coating and methods of manufacturing thereof

Abstract

There is described a method of forming an oxidation resistant coating on a cermet comprising tungsten carbide, tungsten boride, or boron carbide and a metallic binder material. The method comprises exposing the cermet to silicon in the presence of an activator to form a mixture, exposing the mixture to an inert gas, and heating the mixture to a temperature T for a time t, thereby forming a coating on the cermet.

1 . A method of forming an oxidation resistant coating on a cermet comprising tungsten carbide, tungsten boride, or boron carbide and a metallic binder material, the method comprising the steps of:
 (a) exposing the cermet to silicon in the presence of an activator to form a mixture;   (b) exposing the mixture to an inert gas; and   (c) heating the mixture to a temperature T for a time t, thereby forming a coating on the cermet.   
     
     
         2 . The method according to  claim 1 , wherein the cermet comprises 10 wt. % of the metallic binder. 
     
     
         3 . The method according to  claim 1 , wherein the metallic binder material comprises iron, cobalt, nickel, chromium or mixtures thereof. 
     
     
         4 . The method according to  claim 1 , wherein the metallic binder is in the form of a matrix. 
     
     
         5 . The method according to  claim 1 , wherein the activator comprises a halide salt. 
     
     
         6 . The method according to  claim 5 , wherein the halide salt comprises sodium fluoride, sodium chloride, ammonium chloride or potassium tetrafluoroborate. 
     
     
         7 . The method according to  claim 1 , wherein T is in the range from 700 to 1200° C. 
     
     
         8 . The method according to  claim 1 , wherein T is 1000° C. 
     
     
         9 . The method according to  claim 1 , wherein t is from 0.1 to 10 hours. 
     
     
         10 . The method according to  claim 1 , wherein t is from 1 to 4 hours. 
     
     
         11 . The method according to  claim 1 , wherein the inert gas comprises argon and 5 wt % hydrogen. 
     
     
         12 . The method according to  claim 1 , wherein the thickness of the coating formed is from 5 to 500 μm. 
     
     
         13 . The method according to  claim 1 , wherein the thickness of the coating formed is from 40 to 70 μm. 
     
     
         14 . The method according to  claim 1 , further comprising a cooling step (d) to cool the coating and the cermet from temperature T. 
     
     
         15 . The method according to  claim 14 , wherein the coating and cermet are cooled at a rate of from 5 to 10° C. per minute. 
     
     
         16 . The method of  claim 1 , which method comprises a pack cementation process. 
     
     
         17 . The method of  claim 1 , wherein the mixture in step (a) is formed by packing silicon and the activator around the cermet. 
     
     
         18 . A tungsten carbide, tungsten boride, or boron carbide cermet comprising a coating formed in accordance with the method of  claim 1 . 
     
     
         19 . A cermet comprising tungsten carbide, tungsten boride, or boron carbide, a metallic binder material, and an oxidation resistant silicide coating, wherein the surface of the coating substantially consists of silicides of the metallic binder material. 
     
     
         20 . A method of forming an oxidation resistant coating on a cermet comprising tungsten carbide, tungsten boride, or boron carbide and a metallic binder material, the method comprising the steps of:
 a) exposing the cermet to silicon; and   b) heating the mixture to a temperature T for a time t, thereby forming a coating on the cermet.   
     
     
         21 . A method according to  claim 20 , wherein exposing the cermet to silicon comprises exposing the cermet to a vapour including a precursor containing silicon.