HIGH-TEMPERATURE MECHANICAL-BEHAVIOR AND MICROSTRUCTURE OF SIC-WHISKER-REINFORCED MOSI2 COMPOSITES

Composites of MoSi2 reinforced with 20 vol% SiC whiskers and samples o f the unreinforced matrix material fabricated by hot pressing have bee n tested in three-point bending at 1200 degrees C. It is found that bo th materials deform plastically at the test temperature. However, the composites have much higher bending resistance than does the matrix ma terial. The ultimate strengths of the composites and the matrix are ab out 300 MPa and 170 MPa, respectively, as estimated from the load/defl ection curves. Results of SEM and TEM investigations show that there a re many pulled-out whiskers wrapped in a thick layer of matrix phase i n the tensile stress zone on the fracture surface. The interface of Si Cw/MoSi2 is chemically compatible. Stacking faults and a low-melting a morphous phase are also found in the matrix of the composites and are regarded as contributing to the deformation of the materials at high t emperatures. Finally, the strengthening mechanisms of SiCw/MoSi2 compo sites at high temperatures are discussed from the viewpoints of compos ite strengthening and dislocation strengthening. (C) 1997 Elsevier Sci ence Limited.