Reactive Silicon Mandrel for CMC Internal Cavities
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for creating internal cavities in ceramic matrix composite (CMC) articles, such as those using fugitive resins or non-reactive metallic mandrels, face challenges like distortion, complex shape formation, and prolonged processing times due to thermal expansion mismatches and difficulties in mandrel removal.
Innovation Solution
Employing a reactive mandrel made of elemental silicon or silicon alloys that can wet and react with the CMC preform, being absorbed or melted during thermal treatment to form internal cavities without distortion, and maintaining thermal expansion compatibility with the CMC material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional steel mandrels are used to form internal cavities, then the cavity structure can be maintained during lay-up, but the mandrel cannot be removed from the preform due to being captured by shoulders defined by plies
Solution Approach 1:
The invention extracts the problematic steel mandrel from the preform by replacing it with a soluble mandrel material that can be chemically removed. The soluble mandrel is dissolved using an etching solution that selectively removes the mandrel material without affecting the CMC preform, thereby extracting the mandrel from the captured state and leaving a clean cavity.
Solution Approach 2:
The invention changes the chemical parameter of the mandrel material from insoluble (steel) to soluble (material removable by etching). This parameter change enables the mandrel to be removed after lay-up by chemical dissolution rather than mechanical extraction, solving the removal problem while maintaining cavity shape during fabrication.
2Ease of manufacture
If polymeric fugitive resins are used as mandrels, then the mandrel can be removed through decomposition, but the CMC preform distorts during heating due to thermal expansion mismatch
Solution Approach 1:
The invention changes the thermal parameter of the mandrel material by selecting a soluble mandrel with thermal expansion characteristics matched to the CMC preform. This parameter matching eliminates the thermal expansion mismatch that causes preform distortion during heating, while still allowing mandrel removal through chemical dissolution after the preform is cured.
Solution Approach 2:
The soluble mandrel acts as an intermediary that can be selectively removed by chemical etching. The etching solution serves as a mediator that dissolves the mandrel material without affecting the CMC preform, enabling clean removal without the thermal expansion problems of polymeric resins.
3Shape
If fugitive resins are used with larger-size CMC components, then cavities can be formed, but processing cycle time increases due to slower pyrolysis cycles required to escape gases
Solution Approach 1:
The invention changes the removal mechanism from thermal pyrolysis to chemical dissolution. The soluble mandrel is removed by etching after the CMC preform is cured, rather than requiring slow pyrolysis during heating. This parameter change in the removal process eliminates the need for slow gas escape rates during decomposition, significantly reducing processing cycle time for large components.
4Strength
If non-reactive metallic mandrels are used, then the mandrel provides structural support, but the mandrel material does not react with or wet the CMC preform, complicating removal
Solution Approach 1:
The invention uses a composite approach where the soluble mandrel is constructed from materials that provide both structural support and chemical solubility. The mandrel material forms a composite structure that maintains strength during lay-up but can be selectively dissolved by etching solutions, combining the benefits of structural support with ease of removal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method allows for the creation of internal cavities without distortion or deformation, reduces processing time, and enables the formation of complex shapes for weight reduction and cooling purposes, while avoiding the issues associated with non-reactive mandrels and fugitive resins.
Implementation Method 1
The mandrel material wets the CMC preform and reacts with the preform
Implementation Method 2
reacts with the preform and/or is absorbed into the preform during a thermal treatment
Implementation Method 3
The mandrel material wets the CMC preform and reacts with the preform and/or is absorbed into the preform during a thermal treatment
Data Source
AI summary
A process for producing an internal cavity in a CMC article and mandrels used therewith. The process entails incorporating a mandrel made of a material that is substantially absorbed during thermal treatment of a preform to form the CMC article. The mandrel material is preferably reactive with one or more constituents of the CMC preform during the thermal treatment. The material is preferably silicon or a silicon alloy.