Methods to eliminate mudcracks in CMC matrix by humidity controlled atmosphere

Patent metadata

Field	Value
Publication number	US-12233572-B2
Application number	US-202017015840-A
Country	US
Kind code	B2
Filing date	Sep 9, 2020
Priority date	Sep 10, 2019
Publication date	Feb 25, 2025
Grant date	Feb 25, 2025

Abstract

Methods of reducing dry crack formation in ceramic matrix composite green bodies are provided. Some of the methods expose the green body to a gaseous atmosphere at a relatively high humidity for a first period, and then slowly lower the humidity over a second period, where the gaseous atmosphere is at room temperature for both periods. Other methods start the gaseous atmosphere at room temperature and then raise the temperature to a higher temperature while the humidity is relatively high, and hold that temperature even as the humidity is lowered in the second period.

First claim

What is claimed is:

1. A method of reducing dry crack formation in a ceramic matrix composite, the method comprising:
exposing an outer surface of a green body to a gaseous atmosphere having a first humidity for a first period of time at room temperature, the green body being a slurry-infiltrated ceramic fiber preform comprising a plurality of fiber plies or a plurality of prepreg tape layers comprising fibers, the first humidity being a relative humidity within a range of about 40 percent to 100 percent, the first period of time being within a range of about six hours to about 12 hours; and
reducing the humidity of the gaseous atmosphere, while the outer surface of the green body is exposed to the gaseous atmosphere at room temperature, from the first humidity to a second humidity over a second period of time, the second humidity being a relative humidity within a range of about 50 percent to about 65 percent or within a range of about 45 percent to about 60 percent, the second period of time being within a range of about 12 hours to about 18 hours.

2. The method of claim 1 , wherein the first humidity is a relative humidity within a range of about 81 percent to about 95 percent.

3. The method of claim 1 , wherein the first period of time is about 12 hours, and the second period of time is about 12 hours.

4. The method of claim 1 , wherein reducing the humidity of the gaseous atmosphere over the second period of time comprises reducing the humidity of the gaseous atmosphere without any increase in the humidity of the gaseous atmosphere during the second period of time.

5. The method of claim 1 , wherein reducing the humidity of the gaseous atmosphere over the second period of time comprises reducing the humidity of the gaseous atmosphere substantially linearly during the second period of time.

6. The method of claim 1 , wherein reducing the humidity of the gaseous atmosphere over the second period of time comprises reducing the humidity of the gaseous atmosphere substantially exponentially during the second period of time.

7. The method of claim 1 , wherein reducing the humidity of the gaseous atmosphere over the second period of time comprises reducing the humidity of the gaseous atmosphere more slowly during a first part of the second period of time than during a second part of the second period of time.

8. The method of claim 1 , wherein reducing the humidity of the gaseous atmosphere over the second period of time comprises reducing the humidity of the gaseous atmosphere faster during a first part of the second period of time than during a second part of the second period of time.

9. The method of claim 1 , wherein the first humidity limits moisture differentials within the green body during the first period of time as compared to a humidity that is lower than the first humidity, and wherein exposure of the outer surface of the green body to the first humidity during the first period limits a moisture differential within the green body during the second period.

10. The method of claim 1 , wherein the gaseous atmosphere includes air at one atmosphere of pressure.

11. The method of claim 1 further comprising sintering the green body.

Assignees

• Rolls Royce High Temperature Composites Inc

Inventors

• Sellappan Pathikumar
• Shim Sungbo

Classifications

• C04B35/64

  Burning or sintering processes (C04B33/32 takes precedence {; powder metallurgy B22F}) · CPC title

• C04B2235/65

  Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes · CPC title

• C04B2235/616

  Liquid infiltration of green bodies or pre-forms · CPC title

• C04B2235/6588

  Water vapor containing atmospheres · CPC title

• C04B2235/6567

  Treatment time · CPC title