CVI Ceramic Matrix Composite Structures with Graded Preform Pore Sizes
Solution Overview
Problem
Ceramic matrix composite (CMC) structures fabricated using chemical vapor infiltration (CVI) often exhibit significant porosity, particularly in the center, which affects in-plane and inter-laminar properties and oxidation resistance, and becomes more pronounced with increasing thickness.
Innovation Solution
The method involves associating preform plies with different average pore sizes and subjecting them to CVI processing, where the preform plies with larger pore sizes at the outer surfaces and smaller pore sizes at the center facilitate more uniform densification, reducing porosity and enhancing density uniformity throughout the CMC structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If preform plies with uniform pore sizes are used throughout the structure, then the manufacturing process is simple, but significant porosity develops particularly in the center of the CMC structure
Solution Approach 1:
The patent applies local quality by assigning different average pore sizes to different regions of the preform. Specifically, preform plies at the center are designed with larger average pore sizes to facilitate vapor infiltration and densification, while preform plies at the outer surfaces have smaller average pore sizes. This regional differentiation resolves the contradiction by optimizing porosity control in the center without compromising manufacturing feasibility.
2Length of stationary object
If preform thickness is increased to achieve desired component dimensions, then the component can reach required size, but porosity significantly increases and impacts in-plane and inter-laminar properties
Solution Approach 1:
The patent addresses the thickness-related porosity issue by implementing local quality through spatially varying pore sizes. Thicker central regions are equipped with preform plies having larger average pore sizes that promote vapor diffusion and matrix deposition, thereby maintaining density uniformity throughout the thick structure. This approach enables manufacturing of thick CMC components with controlled porosity and improved density uniformity.
3Productivity
If conventional CVI processing is used on thick preforms, then the process can be completed, but the center sections remain poorly densified with high porosity
Solution Approach 1:
The patent applies parameter changes by modifying the pore size parameter of preform plies based on their location. Center preform plies are designed with larger average pore sizes compared to outer plies. This parameter variation enhances vapor infiltration into the center regions during CVI processing, improving matrix deposition and densification in previously under-densified center sections while maintaining overall processing completion.
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 approach results in a CMC structure with improved density uniformity and reduced porosity, leading to enhanced mechanical properties and oxidation resistance, particularly by ensuring that the center sections are densified more uniformly compared to structures with common pore sizes across all plies.
Implementation Method 1
The preform can be subject to chemical vapor infiltration processing (CVI) to define a ceramic matrix composite (CMC) structure. Within the reaction chamber at an elevated temperature the preform can be exposed to certain gasses. On being exposed to the certain gasses at an elevated temperature, a reaction can occur and solid material termed matrix can be deposited on fibers of the preform.
Data Source
AI summary
According to a method set forth herein a plurality of preform plies having first and second preform plies can be associated together to define a preform. The preform can be subject to chemical vapor infiltration (CVI) processing to define a ceramic matrix composite (CMC) structure.