Details of the fabrication and microstructures of hot-machining is a costly process, with limitations on the complexity of machined shapes. These types of considerations have pressed MoSi 2 reinforced-Si 3 N 4 matrix composites were investigated as a function of MoSi 2 phase size and volume driven efforts at developing near-net-shape fabrication methodologies for Si 3 N 4 components, but even here some final dia-fraction, and amount of MgO densification aid. No reactions were observed between MoSi 2 and Si 3 N 4 at the fabrication mond machining is usually required. These considerations also have led to attempts to fabricate composites with electrically temperature of 1750؇C. Composite microstructures varied from particle-matrix to cermet morphologies with increas-conductive phases in the Si 3 N 4 matrix. 6,7
The mechanical behavior of MoSi2 reinforced–Si3N4 matrix composites was investigated as a function of MoSi2 phase content, MoSi2 phase size, and amount of MgO densification aid for the Si3N4 phase. Coarse‐phase MoSi2‐Si3N4 composites exhibited higher room‐temperature fracture toughness than fine‐phase composites, reaching values >8 MP·am1/2. Composite fracture toughness levels increased at elevated temperature. Fine‐phase composites were stronger and more creep resistant than coarse phase composites. Room‐temperature strengths >1000 MPa and impression creep rates of ∼10−8 s−1 at 1200°C were observed. Increased MgO levels generally were deleterious to MoSi2‐Si3N4 mechanical properties. Internal stresses due to MoSi2 and Si3N4 thermal expansion coefficient mismatch appeared to contribute to fracture toughening in MoSi2‐Si3N4 composites.
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