611 アルミナ/NiAl 複合材料の表面自己組織化による強靱化

Abstract

Tri-layer composites consisting of surface layers with residual compressive stress and a stress-tolerant inner layer have been fabricated by the oxidation of alumina-matrix composites dispersing intermetallic NiAl. The residual surface stress is generated by the volume expansion due to the formation of NiAl_2O_4. The starting Al_2O_3-NiAl powder was prepared by heating the precursor mixture of α-Al_2O_3 powder for the matrix and (Ni, Al)-hydradino-benzoate precipitate of at 1200℃ in Ar. The fracture toughness of. the 10vol%NiAl-Al_2O_3 composites was 6.3MPa・m^<1/2>, indicating the suitability as the inner layer material applied under tensile stress. The measured surface compressive stress for the tri-layer composites was more than 120MPa and this stress improved the fracture toughness to 1.5 times of the dispersion composites at the degree of oxidation of 85%. However, when the surface oxidation progressed to more than 90%, much defects formed at the boundary of the surface and inner layers to relax the stress and degrade the toughness.