The effect of microstructure on toughness of Ni/Al2O3 composites prepared by spark plasma sintering

Dense Ni/Al2O3 composites with different microstructures were fabricated using the spark plasma sintering technique. The toughness of the composites is improved by 49% when a larger percentage of nickel particles are present within the alumina grains. Microcracks and dislocations caused by nickel were observed by transmission electron microscopy and crack deflection and ductile particle bridging by scanning electron microscopy. The thermal stress and critical grain size of the second phase were calculated, to explain the initiation of microcracks and the toughening mechanisms are discussed.