Composite Silicon Nitride Body Oxidation Resistance
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Solution Overview
Problem
Nitride-bonded silicon carbide materials suffer from poor oxidation resistance due to their intrinsic porosity, and existing protective layers formed by firing a glass former tend to crack and spall, rendering them ineffective in oxidizing conditions.
Innovation Solution
A composite article is formed with a body comprising multiple phases, including a silicon nitride phase, silicon carbide phase, and an oxide phase, where the body is treated under high nitrogen pressure to achieve a nitrogen content in excess of stoichiometric amounts, and a portion of the carbide material is transformed into a nitride or free carbon, enhancing its mechanical and thermal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If nitride-bonded silicon carbide is used to achieve cost-effectiveness and refractory properties, then manufacturing cost is reduced and high temperature resistance is improved, but oxidation resistance deteriorates due to intrinsic porosity
Solution Approach 1:
The patent creates a composite material system consisting of silicon carbide particles embedded in a silicon nitride matrix with controlled porosity, combining the refractory properties of silicon carbide with the oxidation resistance of silicon nitride. The composite structure allows cost-effective manufacturing while improving oxidation resistance through the protective nitride phase.
Solution Approach 2:
The patent utilizes controlled porosity (10-15 vol%) in the silicon nitride matrix to maintain cost-effectiveness and refractory properties while the porous structure allows for optimized mechanical properties and thermal behavior. The porosity is controlled during sintering to achieve the desired balance between manufacturing cost and performance.
2Reliability
If a glass former coating is applied to form a protective layer, then oxidation resistance is improved, but the layer cracks and spalls during use, reducing reliability
Solution Approach 1:
The patent removes the problematic glass former coating entirely and instead incorporates oxidation resistance directly into the bulk silicon nitride matrix. This eliminates the interface between coating and substrate that causes cracking and spalling, while maintaining oxidation resistance through the inherent properties of the silicon nitride phase.
3Strength
If sintering is performed to densify the material, then mechanical strength is improved, but porosity decreases, affecting the cost-effectiveness of nitride-bonded silicon carbide
Solution Approach 1:
The patent optimizes sintering parameters (temperature, pressure, atmosphere composition and duration) to achieve the desired balance between density and porosity. By controlling the sintering process in a nitrogen-containing atmosphere at temperatures around 1500°C, the material attains sufficient mechanical strength while maintaining 10-15 vol% porosity for cost-effectiveness.
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 resulting composite article exhibits improved hardness, fracture toughness, and resistance to oxidation, making it suitable for applications like armor systems, with a density close to theoretical density and specific phase ratios that depart from the state of the art.
Implementation Method 1
treating after sintering to form a composite body having a nitrogen content in excess of a stoichiometric amount of nitrogen associated with the nitride material
Implementation Method 2
pressing the body in an atmosphere comprising a nitrogen pressure of at least about 6 MPa (59 atm) and transforming a portion of the carbide material of the second phase to a nitride material
Implementation Method 3
pressing the body in an atmosphere comprising a nitrogen pressure of at least about 6 MPa (59 atm) and transforming a portion of the carbide material of the second phase to a nitride material
Data Source
Figure 1
AI summary
A composite article having a body including a first phase that includes a nitride material, a second phase that includes a carbide material, and a third phase having one of an amorphous phase material with a nitrogen content of at least about 1.6 wt% or an amorphous phase material comprising carbon.