Abstract
The work carried out a study of the crack resistance K₁c, calculated theoretically and experimentally determined during mechanical tests, for two systems of ceramic composite materials based on silicon nitride. 1. Electrical materials of the Si₃N₄–SiC system were obtained by reaction sintering. The grain size of the base (Si₃N₄) was 1-2 μm, the SiC additive varied in size from 1-5-120 μm and content of 0, 10, 20, 30%. 2. Structural materials of the Si₃N₄–TiN system were obtained by hot pressing. The grain size of the base (Si₃N₄) was 1-2 μm, TiN additive varied in size 1-5-30 microns and content 0, 10, 20, 30, 40, 50%. Based on theoretical concepts [1] the values of crack resistance K₁c of composites with known K₁c values for pure components were determined by calculation. Theoretical concentration dependences of crack resistance were obtained, which are curves with a maximum in the range of additive concentrations of 20-30%. By testing the bending of notched beams for all materials of the Si₃N₄–SiC and Si₃N₄–TiN system (both for pure components and for composites for all concentrations and grain sizes of the additive), the K₁c values were experimentally determined. A fairly good agreement between the experimental and calculated values of K₁c was obtained for all materials studied, with the discrepancy being less 5 %. In the case of a coarse-grained additive, the discrepancy between theory and experiment was large. This is explained by the high stress concentration in large grains and, therefore, even a small number of large grains lead to a sharp decrease in K₁c. As a result of the research it was found that physical patterns of changes in the crack resistance of composite materials depending on the concentration of components. A fairly good agreement between theory and experiment was obtained using the example of binary systems Si₃N₄–SiC and Si₃N₄–TiN (the discrepancy between the theoretical and experimental values of crack resistance does not exceed 5%).
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