Atomic disorder and phase transformation in L12-Ni3Al by mechanical milling

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Abstract
Mechanical milling of the ordered L12‐Ni3Al was performed in a high‐energy ball mill. The milling process was monitored by x‐ray diffraction, high‐field magnetization, acmagnetic susceptibility, and differential scanning calorimetry(DSC). It was found that antisite disorder is generated in the early stages of milling and a phase transformation from the disordered L12 compound to the disordered fcc solid solution of Al in Ni was observed after milling for long periods. Partial amorphization occurs after prolonged periods of milling. The long‐range‐order parameter decreases monotonously with time in the early stages of milling and attains a zero value after relatively short periods of milling. The lattice parameter and the relative strain increase with milling time. Magnetic properties of ball‐milled Ni3Al at 4.2 K differ markedly from those of the ordered state. Based on the magnetic data, it is concluded that short‐range disordering could be the third source of energy storage during milling of Ni3Al. Exothermic heat effects resulting from atomic reordering and phase restoration and/or crystallization are evident in the DSC scans of ball‐milled Ni3Al.