Microstructure and mechanical properties of Al2O3/Ni composites

Ni-coated Al2O3 powders were prepared by the heterogeneous precipitation method. After hot-pressing at 1300–1450 °C and 20 MPa, the density of homogeneous Al2O3/Ni composites ranges from ∼98% (NA4) to ∼94% (NA8.5) of the theoretical density. Examination by transmission electron microscope (TEM) and scanning electron microscopy (SEM) shows micrometer-size Ni grains to be located at the triple junctions, and with increasing Ni content, the fracture mode of Al2O3/Ni composites to change from intergranular mode to transgranular mode due to the thermal stresses. The strength and toughness of composites was much higher than that of the dense monolithic Al2O3. The strengthening and toughening mechanisms of the composites with respect to the microstructure are analyzed.