Characterization, Formation Mechanism, and Thermodynamics of Nanocrystalline Ni3Si Powder Prepared by Mechanical Alloying

Ni3Si nanocrystalline powder was synthesized by mechanical alloying using a mixture of Ni and Si powders as raw materials. The structure and phase evolution, thermal stability and formation mechanism of Ni3Si powders during mechanical milling were investigated. The results showed that the intermediate phases Ni31Si12 and Ni74Si26 were formed firstly during high energy ball milling. After milling for 30 h, the Ni3Si nanocrystalline powder was finally attained by a series of reactions. Thermal analysis showed that the milled Ni3Si powder was stable during an annealing at 900°C for 2 h. Annealing of the milled powder leads to grain growth, decrease of microhardness, and transformation from disordered structure to ordered structure. Based on Miedema’s semi-empirical theory, the thermodynamic assessment calculation of Ni–Si powder mixtures during mechanical alloying was carried out. The thermodynamic calculation results are in accordance with the experiments.