The formation of aluminides in intermetallic nickel aluminide-based nanocomposites

Metal matrix composites based on the intermetallic alloy Ni3Al 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 Ni3Al in intermetallic nickel aluminide-based composites were observed by measuring the saturation magnetization (Ms) values of the sintered materials. The sample's Ms 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 × 104 J/mol. Addition of 5% alumina increased the hardness of the composite by about a factor of two with respect to that of Ni3Al intermetallic. X-ray diffraction (XRD) measurements showed peaks corresponding to Ni-Al and Ni3Al. 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.