Ceramic Matrix Composite Surface Layer Machining
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Solution Overview
Problem
The existing methods for forming surface layers on ceramic matrix composite (CMC) articles often result in increased cracking and longer machining times due to the brittleness and hardness of the surface layers, which can lead to dimensional inaccuracies and increased costs.
Innovation Solution
A method involving the deposition of a slurry containing ceramic particles, a binder, and a plasticizer on an infiltrated CMC, followed by machining before melt infiltration, which reduces cracking and machining time by increasing the flexibility and hardness of the surface layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a surface layer is formed on CMC without binder and plasticizer, then the surface layer is hard, but it becomes brittle and cracks during machining
Solution Approach 1:
The surface layer is formulated as a composite material containing ceramic particles (70-90 vol.%), binder (1-10 wt.%), and plasticizer (1-15 wt.%). This composite structure combines the hardness of ceramic particles with the flexibility provided by binder and plasticizer, resolving the contradiction between hardness and crack resistance during machining.
Solution Approach 2:
The invention changes the chemical composition parameters of the surface layer by introducing binder and plasticizer components. This modifies the physical properties of the surface layer, making it less brittle while retaining sufficient hardness for machining operations, thus preventing cracking during the machining process.
2Manufacturing precision
If machining is performed after melt infiltration, then the CMC article has final dimensional accuracy, but the total machining time and cost increase
Solution Approach 1:
The invention performs preliminary machining of the surface layer before melt infiltration. Since the surface layer is softer and more machinable at this stage, the majority of material removal can be done efficiently. After infiltration, only minimal finishing operations are needed to achieve final dimensional accuracy, significantly reducing total machining time and cost.
3Loss of time
If the surface layer is machined when soft, then machining time is reduced, but the surface layer lacks sufficient hardness for proper machining
Solution Approach 1:
The invention optimizes the binder and plasticizer content to achieve a specific hardness range that is softer than conventional surface layers. This modified hardness parameter allows the surface layer to be machined more easily while still maintaining sufficient structural integrity, enabling reduced machining time without compromising machinability.
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 CMC articles with fewer cracks and reduced machining time and cost, as the binder enhances adhesion and the plasticizer increases flexibility, allowing for smoother handling and processing.
Implementation Method 1
The binder in the surface layer during drying may further increase adhesion between particles in the surface layer to reduce cracking in the surface layer
Implementation Method 2
Presence of the plasticizer in the surface layer during machining may increase a flexibility and reduce a brittleness of the surface layer to reduce chipping and cracking
Implementation Method 3
drying the slurry to form an article having an outer surface layer that includes the solid particles on the infiltrated CMC
Implementation Method 4
infiltrating the article with a molten infiltrant to form a composite article
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The disclosure describes a method for forming a surface layer of a ceramic matrix composite (CMC) article. The technique includes depositing (46) a slurry (28) on a surface (24) of an infiltrated CMC (13). The slurry (28) includes a carrier material (36), a binder (38), a plasticizer (40), and solid particles (16). The solid particles (16) include a plurality of fine ceramic particles (32) defining a fine particle average size less than about 5 micrometers. The method further includes drying (48) the slurry (28) to form an article (10) having an outer surface layer (17) that includes the solid particles (16) on the infiltrated CMC (13). The method further includes machining (50) at least a portion of the outer surface layer (17) of the article (10). The method further includes infiltrating (52) the article (10) with a molten infiltrant to form a composite article.