Strength of sintered Mo-Al₂O₃ and Mo-ZrN composite materials

Conclusions

The strength of solid-phase-sintered Mo-Al₂O₃ composites containing up to 30 vol. % of the oxide increases and their porosity decreases with rise in sintering temperature up to 1800°C. At still higher sintering temperatures the strength falls, although the density continues to grow. The fall in strength is a result of a weakening of the phase boundary bonds. Liquid-phase sintering lowers the strength by intensifying reactions at the phase boundaries, with the evolution of MoO, MoO₂, and MoO₃ vapors. The gaseous products form macropores which become crack nuclei during rupture. The fracture of the composites commences with the cracking of particles of the hard phase under the action of an internal cleaving stress. The strength of the composites depends on the size and shape of the strengthening particles and of the matrix grains. With increasing matrix grain size the strength at first grows and then falls. In the Mo-ZrN system the strength of adhesion exceeds the strength of cohesion (σ_A−B > σ_A,σ_B), while in the Mo-Al₂O₃ system the situation is reversed.