Abstract: Si₃N₄, TiC and SiC whisker reinforced SiC matrix composites were Hot Isostatically Pressed, and the microstructure and mechanical
properties were studied. The strengthening and toughening mechanisms are different depending on the incorporation of second phase. Si₃N₄ in
the matrix may induce the radius compressive force because of the difference of thermal expansion coefficient and elastic modulus. As
a result, the crack propagation will be hindered. TiC in the matrix will induce the radius tension force so that the crack will be deflected.
The incorporation of SiC_W can produce the composed strengthening and toughening mechanism such as crack deflection, pull out, so that both
of the strength and fracture toughness will be improved.

Key words: hot isostatic pressing, composite, strengthening and toughening, microstructure, mechanical properties