Diffusion coatings for metal-based substrate and methods of preparation thereof

Patent metadata

Field	Value
Publication number	US-9909019-B2
Application number	US-201514749096-A
Country	US
Kind code	B2
Filing date	Jun 24, 2015
Priority date	Jun 24, 2015
Publication date	Mar 6, 2018
Grant date	Mar 6, 2018

Abstract

The present invention is directed to coating compositions for forming diffusion coatings on metal-based substrates. The coating compositions may include a metal powder, an inorganic salt, an activator, and a binder. The present invention is also directed to processes for forming diffusion coatings on metal-based substrates using the disclosed coating compositions.

First claim

What is claimed is:

1. A process for forming a diffusion coating on a metal-based substrate, the process comprising:
(a) applying a coating composition onto the metal-based substrate to form a coating layer on the metal-based substrate, the coating composition comprising a metal powder, a ternary mixture of three inorganic salts having a melting point that is less than or equal to 800° C., an activator, and a binder, wherein the ternary mixture is selected from the group consisting of LiF—NaF—MgF 2 , LiCl—KCl—CaCl 2 , and LiF—PuF 3 —ThF 4 , and wherein the ternary mixture is present in an amount from about 37% to about 70% by weight of the coating composition;
(b) drying the coating layer; and
(c) heat treating the coating layer and the metal-based substrate at a temperature in a range from about 800° C. to about 950° C. for a sufficient period of time to melt the the ternary mixture to form a liquid barrier of molten salt, and to form the diffusion coating on the metal-based substrate.

2. The process of claim 1 , wherein the coating composition is a paste when applied to the metal-based substrate in step (a).

3. The process of claim 1 , wherein the metal-based substrate is a nickel based superalloy.

4. The process of claim 1 , wherein the metal powder is selected from the group consisting of a chromium powder, aluminum powder, and mixtures thereof.

5. The process of claim 1 , wherein the metal powder further comprises an additive selected from the group consisting of aluminum, cobalt, nickel, silicon, and mixtures thereof.

6. The process of claim 1 , wherein the metal powder is present in an amount of about 1% to about 60% by weight of the coating composition, the activator is present in an amount from about 1% to about 30% by weight of the coating composition, and the binder is present in an amount of at least 1% by weight of the coating composition.

7. The process of claim 1 , wherein the metal powder is a chromium powder, the diffusion coating has a thickness of about 0.0001 to about 0.003 inches, and wherein the diffusion coating comprises greater than or equal to 45% by weight of chromium.

8. A process for forming a diffusion coating on a metal-based substrate, the process comprising:
(a) applying a first coating composition onto the metal-based substrate to form a first coating layer on the metal-based substrate, the first coating composition comprising a metal powder, an activator, and a first binder;
(b) applying a second coating composition onto the first coating layer formed in step (a) to form a second coating layer on the first coating layer, the second coating composition comprising a ternary mixture of three inorganic salts and a second binder, wherein the ternary mixture is selected from the group consisting of LiF—NaF—MgF 2 , LiCl—KCl—CaCl 2 , and LiF—PuF 3 —ThF 4 the ternary mixture has a melting point that is less than or equal to 800° C., and the ternary mixture is present in an amount from about 50% to about 90% by weight of the second coating composition; and
(c) heat treating the first coating layer, the second coating layer, and the metal-based substrate at a temperature in a range from about 800° C. to about 950° C. for a sufficient period of time to melt the ternary mixture to form a liquid barrier of molten salt, and to form the diffusion coating on the metal-based substrate,
wherein the first coating layer and the second coating layer are dried subsequently to the applying of the second coating composition step (b) and prior to the heat treating step (c), or wherein the first coating layer is dried prior to the applying of the second coating composition step (b) and the second coating layer is dried prior to the heat treating step (c).

9. The process of claim 8 , wherein the first coating composition is a paste when applied onto the metal-based substrate in step (a), and wherein the second coating composition is a paste when applied onto the first coating layer in step (b).

10. The process of claim 8 , wherein the metal-based substrate is a nickel based superalloy.

11. The process of claim 8 , wherein the metal powder is selected from the group consisting of a chromium powder, aluminum powder, and mixtures thereof.

12. The process of claim 8 , wherein the metal powder further comprises an additive selected from the group consisting of aluminum, cobalt, nickel, silicon, and mixtures thereof.

13. The process of claim 8 , wherein the metal powder is present in an amount of about 1% to about 60% by weight of the first coating composition, the activator is present in an amount of about 1% to about 30% by weight of the first coating composition, and the first binder is present in the amount of at least 1% by weight of the first coating composition.

14. The process of claim 8 , wherein the metal powder is a chromium powder, the diffusion coating has a thickness of about 0.0001 to about 0.003 inches, and wherein the diffusion coating comprises greater than or equal to 45% by weight of chromium.

Assignees

• Gen Electric

Inventors

• Wang Limin
• Kool Lawrence Bernard

Classifications

• C23C10/58

  more than one element being diffused in more than one step · CPC title

• C23C10/32

  Chromising · CPC title

• C23C10/02

  Pretreatment of the material to be coated (C23C10/04 takes precedence) · CPC title

• C09D7/1216 Primary

  Chemistry & Metallurgy · mapped topic

• C08K2003/164

  Aluminum halide, e.g. aluminium chloride · CPC title