Synthesis of metastable NiGe2 by mechanical alloying

Mechanical alloying of Ni-Ge elemental powder blends was carried out in a high-energy SPEX shaker mill to study phase evolution as a function of milling time. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy techniques were employed to characterize the phases present in the milled powders. It was noted that a supersaturated solid solution formed in the early stages of milling containing up to about 12 at.% Ge. On continued milling, the equilibrium NiGe phase started to form at 5 h, ancrits amount in the powder increased with increasing milling time. On milling for about 60 h, the equilibrium intermetallic NiGe and Ge powder particles reacted to form the metastable NiGe2 phase. Reasons for the formation of this metastable phase at room temperature and at atmospheric pressure, which is normally present at high temperatures and under high pressures, have been discussed. (C) 2015 Elsevier Ltd. All rights reserved.