Effects of milling temperature and time on phase evolution of Ti-based alloy

Abstract

Ti50Cu25Ni20Sn5 (at.%) powder was subjected to high-energy ball milling at room temperature and -78?C. As a function of the milling time, evaluation of phases, morphology and the refinement of grain size were investigated by scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and laser-diffraction particle size analysis (PSA). The transformation of the crystalline structure into an amorphous structure and then the transformation into a nanocrystalline structure during further milling was detected. The stress-induced martensitic transformation has taken place after 30 min milling time at both temperatures, the cubic Cu(Ni,Cu)Ti2 phase transforms into the orthogonal structure. The hardness value of powders after 150 min milling time increases from 506 to 780 HV0.01. The milling temperature does not significantly influence the amount of amorphous fraction (33-36 wt.%) but the composition of amorphous content is more influenced by temperature. The interval of crystallite size was between 1.2 and 11.7 nm after 180 min of milling. The amount and the cell parameters of the Sn-containing phases are different between the two milling experiments, owing to the diffusion coefficients of the Sn atom differ to a large extent.