Atomic disorder and phase transformation in L1 2-structure Ni 3Si by ball milling

Abstract

The structural evolution of the L1 2-compound Ni 3Si upon ball milling was followed by X-ray diffraction, high-field magnetization measurement and differential scanning calorimetry (DSC). Anti-site disorder was generated in the early stages of milling and a phase transformation from the disordered L1 2-compound to the nanocrystalline f.c.c. solid solution of silicon in nickel was observed after milling for long periods. The long-range-order parameter decreases monotonously with time in the early stages of milling and reaches zero after long periods of milling. The lattice parameter and unit-cell volume also decrease gradually in the early stages of milling. A discontinuous decrease of the lattice parameter is observed during the phase transformation. The magnetic behaviour at 4.2 K of ball-milled samples differs from that of the starting compound. Exothermic peaks resulting from atomic reordering and phase restoration are evident in the DSC scans of ball-milled samples. The variation of the transition heat and temperature with milling time in the intermediate stages gives more insight into the process of phase transformation.