Effect of Ni content and Al₂O₃ particle size on the thermal and mechanical properties of Al₂O₃/Ni composites prepared by spark plasma sintering

Alumina-nickel composites were prepared by carrying out spark plasma sintering (SPS) of nano-sized and micro-sized Al₂O₃ particles with 15–45 wt% Ni powders. The powder materials were sintered at a temperature of 1400 °C under a constant uniaxial pressure of 50 MPa. FESEM micrographs of the products showed uniformly dispersed nickel inclusions in both matrices at intergranular positions. Presence of Al₂O₃ as the major phase along with Ni as the minor phase was confirmed using XRD analysis. Thermal and mechanical properties of the nano- and micro-sized Al₂O₃/Ni composites were investigated. The thermal conductivity of nano-sized alumina composites was seen to increase with the increase in nickel content, however, an opposite trend was observed for micro-sized alumina-based composites. Moreover, thermal conductivities of all the composites decreased with increase in temperature. The composites also showed high hardness and fracture toughness values of up to 19.6 GPa and 4.71 MPa ∗ m^1/2, respectively, and relative density values, between 79 and 99%, that decreased with increasing Ni content. Furthermore, the nano-sized Al₂O₃/Ni composites showed thermal and mechanical properties superior to those of the micro-sized Al₂O₃/Ni composites.