ZIRCONIA-TOUGHENING OF NICKEL ALUMINIDE

The fracture toughness and strength behaviour of nickel aluminide toughened by partially stabilized zirconia dispersoids was investigated in the range zirconia content up to 40 vol.%. In addition, the temperature dependence of the mechanical properties was examined. Composites were fabricated using attrition milling followed by hot uniaxial pressing of powder mixtures. A considerable increase in fracture toughness and bending strength is achieved by adding zirconia particles. The maximal level of the mechanical properties corresponds to zirconia content in the range 20-25 vol. %. A positive temperature dependence of the fracture toughness was established up to 500-degrees-C. It was concluded, on the basis of residual stress analysis, that room-temperature toughening is due to mainly stress-induced phase transformation. A positive temperature dependence of toughening can be attributed to an increase in the stress relaxation near the crack tip.