Effect of MoSi2 and Nb reinforcements on mechanical properties of Al2O3 matrix composites

The room temperature mechanical properties of Al₂O₃ composites reinforced with 25 vol% of either MoSi₂ or Nb particulates were investigated. It was found that addition of Nb particles resulted in a reduction in the elastic modulus, but caused a significant increase in both flexural strength and fracture toughness. On the other hand, the addition of MoSi₂ particles resulted in only a marginal decrease in elastic modulus and marginal increase in both flexural strength and fracture toughness. The elastic modulus results were explained on the basis of Tsai - Halpin model. For both the composites, the increase in flexural strength was attributed to the grain refinement of the Al₂O₃ matrix as well as the load transfer to the reinforcement particles. The marginal increase in fracture toughness in Al₂O₃ / MoSi₂ composites was attributed to crack deflection, whereas the threefold increase in fracture toughness in Al₂O₃ / Nb composites was attributed to crack blunting and bridging.