Wear resistant coating
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 localized 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; and
(b) heating the feed and the substrate to cause the commercially pure titanium or titanium alloy particles, at least some of the titanium nitride particles and the localized surface of the substrate to melt to form a melt pool;
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 substrate is a component of an autoclave.
3. The method defined in claim 2 , wherein the autoclave component is an agitator.
4. The method defined in claim 1 , wherein the corrosive and abrasive environment comprises autoclave processing conditions that extract valuable minerals from a mined ore.
5. The method defined in claim 4 , wherein the corrosive and abrasive environment comprises autoclave processing conditions involving an elevated pressure in the range of 30 to 52 atm, temperatures in the range of 120° C. to 270° C. and acid addition to a slurry of ground ore and water of 200 to 500 kg/t of ore.
6. A method as defined in claim 1 , wherein the method involves depositing one or more layers of the wear resistant coating on the substrate to build up the thickness of the wear resistant coating.
7. A method as defined in claim 1 , wherein the method further comprises carrying out steps (a) and (b) while the substrate is exposed to the ambient atmosphere.
8. A method as defined in claim 1 , wherein the method further comprises a step of pre-treating the substrate to remove contaminants.
9. A method as defined in claim 8 , wherein the pre-treating step is carried out while the substrate is in contact with the ambient atmosphere.
10. A method as defined in claim 8 , wherein the surface pretreatment step is selected to remove oxygen, iron and other contamination.
11. A method as defined in claim 8 , wherein the pretreatment step involves removing a contaminated surface layer from the substrate.
12. A method as defined in claim 1 , wherein the method further comprises controlling the temperature of the molten material to be between the melting temperature of titanium and the vaporisation temperature of titanium.
13. A method as defined in claim 1 , wherein the method comprises controlling phases of titanium nitride formed upon solidification of the molten materials by controlling the time that the molten material remains molten.
14. A 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 150° C.
15. A method as defined in claim 1 , wherein the method further comprises controlling conditions to form the wear resistant and galling resistant coating with a matrix of titanium nitride having a hardness in the range of 400 Hv to 550 Hv.