The formation of aluminides in intermetallic nickel aluminide-based nanocomposites

Abstract Metal matrix composites based on the intermetallic alloy Ni 3 Al and alumina were fabricated using powder metallurgy technique. Nanosize alumina as dispersed phase was mixed with Ni and Al powder in a planetary ball mill for 4 h at 350 rpm to achieve a small mechanical alloying effect. The mixture was then compacted using a hydraulic press at 400 MPa for 15 min. Sintering was performed under an inert condition in a tube furnace at 660 °C with 5 h soaking time. The formation of aluminides, Ni–Al and Ni 3 Al in intermetallic nickel aluminide-based composites were observed by measuring the saturation magnetization ( M s ) values of the sintered materials. The sample's M s value was very low at 0.9222 emu/g indicating the presence of a small amount of elemental Ni. The occurrence of reaction synthesis during sintering was detected by the presence of a ‘large’ exothermic peak of the differential thermal analysis curve, which occurred at below 600 °C. The heat released during reaction synthesis was probed by differential scanning calorimetry. The heat of reaction was found to be 4.53 × 10 4 J/mol. Addition of 5% alumina increased the hardness of the composite by about a factor of two with respect to that of Ni 3 Al intermetallic. X-ray diffraction (XRD) measurements showed peaks corresponding to Ni–Al and Ni 3 Al. Optical and SEM investigations revealed growth of lath-like microstructure in the fabricated composite due to a high lattice mismatch between γ and γ′ phase.