Phase Evolution by Annealing of Mechanically Activated Ni, Mn, and Sn Elemental Powders Mixture with the Ni2MnSn Heusler Compound Ratio.

A Ni2MnSn Heusler alloy composition of elemental powders was high-energy milled for a short time for powder activation. The milling times were chosen to be 1 and 4 h to study how mechanical mixing triggers the phase formation in the Ni-Mn-Sn system. After milling, the samples were analyzed by differential scanning calorimetry and the thermal events of Ni2MnSn L21 phase formation were investigated. The milled samples were compacted at 700 MPa and annealed in a vacuum for 10 min at different temperatures (230 °C, 330 °C, and 600 °C). The annealing temperatures were chosen to emphasize the activated powders' behavior before and after Sn melting on L21 Structure formation. Using X-ray diffraction and Rietveld analysis, the phase quantity was computed, showing that the largest L21 phase (63%) can be obtained from the elemental powder mixture due to Sn melting during the annealing. For milled samples, a Ni3Sn4 phase was obtained by milling, and by annealing this phase, along with the remaining element, it reacts to form a Ni2MnSn L21 phase and a Ni3Sn2 phase. The microstructural evolution of the phase was illustrated by backscattering electron microscopy for milled and subsequent annealed samples, and, by image analysis, a correlation of the phase's amount was performed. The results of the image analysis were correlated with the X-ray diffraction patterns.