Gradient Tow Spacing in CMC Preforms for CVI Infiltration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Ceramic matrix composites (CMCs) 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, due to the difficulty of precursor infiltration through uniform layers.
Innovation Solution
A preform design comprising sub-laminates with varying tow spacings and diameters, creating gradients in pore sizes to facilitate more complete precursor infiltration and achieve uniform matrix density, reducing porosity and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform tow spacing is used in all layers, then manufacturing is simple, but porosity increases significantly in the center of the composite
Solution Approach 1:
The patent applies local quality by varying the tow spacing in different layers of the preform. Specifically, outer layers have smaller tow spacing while inner layers have larger tow spacing, creating a gradient that optimizes precursor infiltration throughout the composite thickness and reduces central porosity.
Solution Approach 2:
The patent changes the geometric parameter of tow spacing across different layers. By systematically varying this parameter from outer to inner layers, the preform creates controlled pore size gradients that facilitate complete precursor infiltration and reduce overall porosity.
2Device complexity
If uniform tow spacing is used in all layers, then the preform structure is simple, but matrix density becomes non-uniform with higher porosity in the center
Solution Approach 1:
The patent implements local quality by assigning different tow spacing values to different spatial locations (layers) within the preform. This creates a non-uniform pore size distribution that compensates for diffusion limitations during CVI, achieving uniform matrix density throughout the composite.
Solution Approach 2:
The patent segments the preform into multiple layers with distinct tow spacing characteristics. By dividing the preform into outer and inner layers with different spacing parameters, the invention enables controlled gradient formation that ensures uniform matrix infiltration.
3Strength
If thicker preforms are used, then structural capacity increases, but porosity increases due to difficulty of precursor infiltration
Solution Approach 1:
The patent applies parameter changes by varying tow spacing as a function of layer position. This creates a pore size gradient that facilitates precursor diffusion through thicker preforms, enabling the use of thicker structures without suffering from excessive central porosity.
Solution Approach 2:
The patent uses local quality to optimize thick preforms by assigning smaller tow spacing to outer layers and larger spacing to inner layers. This creates favorable diffusion conditions throughout the thickness, allowing increased structural capacity while maintaining oxidation resistance.
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
The approach results in ceramic matrix composites with reduced porosity and improved uniformity in matrix density across the thickness, leading to enhanced mechanical properties and extended lifespan.
Implementation Method 1
A preform can include fibers, which can be unidirectional or woven (e.g., plain weave, 5 Harness Satin Weave, 8 Harness Satin Weave, twill, 3-dimensional, 3D biaxial and triaxial braiding). In one form the fibers can be ceramic based and can be formed of silicon carbide (SIC). Within the CVI reaction chamber at an elevated temperature the preform can be exposed to certain precursors. On being exposed to the certain precursors at an elevated temperature, a reaction can occur resulting in the deposition of a ceramic on the fibers of the preform.
Data Source
AI summary
A preform comprising a first sub-laminate comprising a plurality of layers and a second sub-laminate comprising a plurality of layers. The first sub-laminate comprises a first unit cell comprising a first volume fraction of tows, where the first volume fraction of tows comprise first tows having a first tow spacing between successive first tows. The second sub-laminate comprises a second unit cell comprising a second volume fraction of tows, where the second volume fraction of tows comprise second tows having a second tow spacing between successive second tows. The first volume fraction of tows in the first unit cell is equal to the second volume fraction of tows in the second unit cell. The second tow spacing is less than the first tow spacing.