Preparation and properties of Al2O3/Ni composite from NiAl2O4 spinel by in situ reaction sintering method

Al2O3/Ni nano composites were prepared from NiAl2O4 spinel by in situ reaction sintering method. The starting materials of Al2O3–NiO powder were synthesized by thermal decomposition of precipitates prepared from aluminum sulfate and nickel sulfate. The specific surface area of the Al2O3–NiO powder was >36 m2/g. The Al2O3/Ni composites were obtained by firing the starting material buried in a carbon bed at 1500 °C for 1 h. The resulting Al2O3/Ni composites have relative densities >96% (0–40 mol% Ni). Nickel grains dispersed homogeneously in the microstructure, accounting for 10% of within the grains and 90% at grain boundaries. The average particle size of the former nickel grains was 150 nm while that of the latter grains was 300 nm. The maximum three-point bending strength was 408 MPa at 10 mol% Ni sample and the maximum fracture toughness was 9.9 MPa m1/2 at 40 mol% Ni sample. The Vickers hardness decreased slightly with increasing Ni content and this change is in good agreement with individual mixture rule.