Characterization and Formation Mechanism of Ni3Si–Al2O3 Nanocomposite Prepared by Mechanochemical Reduction Method

In this present work, Ni 3 Si–Al 2 O 3 nanocomposite powders were synthesized by mechanical milling using NiO, Si and Al as raw materials. The phase transformation, formation mechanism and microstructure evolution of the powders during mechanical milling were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), transition electron microscopy (TEM) and microhardness measurements. Results showed that the Ni 3 Si, Al 2 O 3 and Ni 31 Si 12 phases formed after 5 h of milling with a rapid mechanically induced self-propagating synthesis mode. The average grain size and internal strain of Ni 3 Si and Al 2 O 3 after 30 h of milling were (16.8 nm, 1.27%) and (19.6 nm, 0.94%), respectively. The maximum microhardness value of 813 HV was obtained in the 30 h milled powder. The relationship between the hardness and grain size of the powders satisfies the Hall–Petch relationship. Ni 3 Si–Al 2 O 3 nanocomposite powders are very stable during heating at 950 °C. By annealing of the milled powders leads to grain growth, internal strain and microhardness of Ni 3 Si powder decrease and transformation of disordered structure to an ordered state. A long-range ordering parameter (LRO) of 0.97 for the ordered Ni 3 Si can be achieved after annealing at 950 °C for 2 h.