Fabrication and mechanical properties of Al2O3–Ni composite from two different powder mixtures

Al2O3–4vol.%Ni composites were prepared by hydrogen reduction and hot pressing of powder mixtures of NiO and Al2O3 obtained by two processes, namely, the ball-milled mixing process (process A) and the coating process (process B). The microstructural features and sintering behavior of the powder mixtures, and mechanical properties of composites were investigated. The samples obtained by hot pressing powder mixtures synthesized through process A and B at 1450 and 1400 °C reached >98% theoretical densities. The microstructural homogeneity of the samples was in agreement with characteristics of two different powder mixtures. Compared with that by process A, the samples fabricated by process B exhibited an increase in toughness and a decrease in strength. The toughening was mainly attributed to crack deflection and crack branching. The difference of strength was discussed through the observed microstructure and fracture model of the composites. The standard deviations (S.D.) of the strength and toughness indicated the samples prepared by process B had better reliability and stability.