Formation and thermal stability of a nanoscale Ti-Fe-Ni powder produced by mechanical alloying

Abstract

A nanoscale Ti50Fe40Ni10 powder was formed by mechanical alloying, and its formation and thermal properties were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential calorimetry (DSC), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The composition of the alloy was determined by using inductivelycoupled plasma-emission spectrometry (ICP). After 400 h of milling (tm), an XRD peak indicating the body-centered cubic (b.c.c.) form was observed at 2θ = 44.5°. From the broadening of the peak, the crystallite size and the internal strain after 100 h of milling were 52.0 nm and 0.0087, respectively, as determined by using the Williamson-Hall and the Scherrer methods. The entire mechanical alloying process can be divided into three different stages: agglomeration (0 tm ≤ 100 h), disintegration (100 h tm ≤ 400 h), and homogenization (400 h ≤ tm ≤ 600 h). The saturation magnetization, Ms, of the powders before milling was 92.0 emu/g; this decreased to 53.6 emu/g with 600 h of milling. The temperature of the DSC curve peak, Tp, was 457.8 °C. In the isothermal experiments, the signal decayed monotonically, demonstrating unambiguously that the transformation was a grain-growth-type process.