Effect of Si, Al₂O₃, and aluminum dross on sinterability and properties of Ni–Ti metal matrix composites prepared by powder metallurgy

In the present work, composites containing Ni–Ti as a matrix and Si, Al₂O₃ and alumium dross (mix of Al and Al₂O₃) as reinforcements were prepared by powder metallurgy technique. The designed mixes were sintered in a low rate argon atmosphere (i.e. with the possiblity for the presence of air) at 1050, 1100 and 1200 °C. The phase indentification of sintered composites was conducted by x-ray diffraction technique. Bulk density and apparent porosity were determined by liquid displacement method according to Archimedes principle. Microstructure of solidified composites was examined by scanning electron microscopy. The hardness of sintered composites was also tested by Vicker indentor. The results revealed that new in situ formed phase as TiO₂ was detected in the sintered composites due to the oxidation of Ti. Generally, the sintered composites composed mainly of metal, alloy and oxides as the main components. Furthermore, the apperent porosity was decreased with increasing sintering temperture and with the addition of reinforcments. The composite that contains 20% aluminum dross showed the minimum porosity. The hardness was also improved with increasing the sintering temperture and after addition of reinforcements (Si, Al₂O₃ and aluminum dross). The composites containing 10 and 20 wt% aluimum dross exhibited the maximum hardness values i.e. 4881 and 4928 MPa, respectively. (paper)