Process for depositing a coating for protection against oxidation and against hot corrosion on a superalloy substrate
View Patent ↗To protect a superalloy substrate from oxidation and hot corrosion, disclosed herein is a process that deposits successive layers on the substrate, a first layer of aluminum and of at least one element capable of being alloyed with sulphur, and a second layer of a material that isolates the at least one element capable of being alloyed with sulphur.
1. A process for protecting a metallic superalloy substrate against oxidation and hot corrosion, the process comprising
depositing, on the metallic superalloy substrate, a first layer of aluminium and at least one element capable of being alloyed with sulphur by a vapour phase aluminization process, and
depositing by chemical vapour deposition a second layer of a material that isolates said element capable of being alloyed with sulphur on the first layer,
wherein the first layer forms a diffusion zone between the metallic superalloy substrate and the second layer with an interface zone between the first and second layers; and
the vapour phase aluminization process is conducted so that the at least one element is alloyed with sulphur and has a concentration peak in the interface zone and coincides with a concentration peak of the sulphur at the interface zone.
2. The process according to claim 1 , further comprising providing a third layer comprising platinum on the second layer.
3. The process according to claim 2 , further comprising applying a diffusion heat treatment to enrich the first layer, the second layer or both with platinum from the third layer.
4. The process according to claim 2 , wherein the third layer further comprises at least 35 wt % of nickel.
5. The process according to claim 4 , wherein the third layer is formed by depositing a layer of platinum followed by depositing a layer of nickel.
6. The method according to claim 2 , further comprising depositing a ceramic layer on the third layer.
7. The process according to claim 1 , wherein the element capable of being alloyed with sulphur is a reactive element or a rare earth element.
8. The process according to claim 1 , wherein the material in the second layer that isolates said element capable of being alloyed with sulphur is aluminium.
9. The process according to claim 1 , wherein the element capable of being alloyed with sulphur is zirconium, hafnium, yttrium, silicon, cerium or lanthanum or gadolinium.
10. The process according to claim 1 , wherein the element capable of being alloyed with sulphur is zirconium.
11. The process according to claim 1 , wherein the depositing of the first layer of aluminium and at least one element capable of being alloyed with sulphur by a vapour phase aluminization process comprises contacting the substrate and an aluminium alloy with a gas in a treatment chamber, the gas comprising a carrier gas and an activator and the activator reacts with the aluminium alloy to form a gaseous aluminium halide that decomposes at the surface of the substrate to deposit aluminium and the element capable of being alloyed with sulphur.
12. The process according to claim 11 , wherein the contacting in the treatment chamber is conducted at a temperature of from 950 to 1200° C.
13. The process according to claim 11 , wherein the element capable of being alloyed with sulphur is zirconium.
14. The process according to claim 13 , wherein the activator is a zirconium salt.
15. The process according to claim 11 , wherein the temperature in the treatment chamber is raised from ambient temperature at a rate of 4 to 20° C. per minute.
16. The process according to claim 11 , wherein the gas is circulated through the chamber when the temperature of the treatment chamber is above 700° C.