Study of the effect of mechanical alloying on the structure of Ni-Mn-Sn Heusler alloy

Abstract

The formation process of nanocrystalline Ni-Mn-Sn Heusler alloy was investigated using mechanical alloying route. Powder samples of this alloy were fabricated using high milling energy technology of planetary ball mill in an argon atmosphere. The effects of selected milling time (0 hr, 5 hr, 10 hr and 15 hr) on the crystallite size, lattice strain, morphology and chemical composition of as-milled powder samples were studied using X-ray diffraction (XRD) and scanning electron microscope (SEM) attached with energy-dispersive Xray spectroscopy (EDX). Thermal behavior of the samples was analyzed by differential scanning caloorimetry (DSC). Results indicated that the formation of single phase Ni2MnSn Heusler alloy was obtained after 15 hr of milling through the balance between particle coalescence and fracture accompanied by uniform grain refinement. The optimum milling time resulted from the proper selection of milling parameters. Compositional analysis of 15 hr asmilled sample revealed stoichiometric Heusler composition (X2YZ) of Ni-Mn-Sn alloy with no impurities. The subsequent heating of the powder particles in DSC showed crystallization of Ni-Mn-Sn alloy. The obtained results provide an understanding of the fabrication of Ni-Mn based Heusler alloy powders by mechanical alloying technique by using laboratory scale ball mill with the aim to bring out structural and thermal aspects of the alloy.