Research and Development of SiC fiber reinforced/ oxide matrix composites for heisht efficiency non-cooling bledes in gas turbine generator

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As a potential material for high temperature services, unidirectional SiC fiber reinforced SiO2-mullite composites were fabricated by slurry impregnation method and liquid phase hot-pressing. A sintered SiC fiber was selected as the reinforcement. The hot-pressing was performed in graphite dies at the conditions of 1923 K, 30 Mpa, 3.6 ks in vacuum. In order to investigate influence of thermal residual stress on the mechanical properties, three levels of matrix composition were selected, I.e., SiO2- 3.7, 30, 50 mol. % Al2O3, to control thermo-elastic mismatch between fiber and matrix.Three-point flexural test was carried out at 298 K and 1573 K. The ultimate strength was nearly 1 Gpa at each test temperature except for the SiO2- 3.7 mol.% Al2O3 matrix composite tested at 1573 K. Thus, the effect of thermal residual stress on the ultimate strength was not remarkable. Furthermore, the effect of the thermal residual stress on the proportional limit of the composites was investigated during three-point flexural test with acoustic emission CAE) monitoring at 298 K. The highest proportional limit was resulted from the highest compressive residual stress in the matrix of SiO2-3.7 mol.% Al2O3 composite. However, no apparent matrix cracking stress was detected by monitoring AE signals during three-point flexural test.The SiO2- 3.7 mol.% Al2O3 matrix composite with large amount of SiO2 glass in the matrix caused plastic deformation of the test pieces at 1573 K. On the other hand, the network structure that the primary mullite crystal bonds each other in the SiO2- 30, 50 mol.% Al2O3 matrix composite was effective to prevent the plastic deformation of the matrices during the flexural test at 1573 K.