High-temperature mechanical behavior and microstructure of SiC-whisker-reinforced MoSi2 composites

Composites of MoSi2 reinforced with 20 vol% SiC whiskers and samples of the unreinforced matrix material fabricated by hot pressing have been tested in three-point bending at 1200 degrees C. It is found that both materials deform plastically at the test temperature. However, the composites have much higher bending resistance than does the matrix material. The ultimate strengths of the composites and the matrix are about 300 MPa and 170 MPa, respectively, as estimated from the load/deflection curves. Results of SEM and TEM investigations show that there are many pulled-out whiskers wrapped in a thick layer of matrix phase in the tensile stress zone on the fracture surface. The interface of SiCw/MoSi2 is chemically compatible. Stacking faults and a low-melting amorphous phase are also found in the matrix of the composites and are regarded as contributing to the deformation of the materials at high temperatures. Finally, the strengthening mechanisms of SiCw/MoSi2 composites at high temperatures are discussed from the viewpoints of composite strengthening and dislocation strengthening. (C) 1997 Elsevier Science Limited.