Effect of milling energy on phase transformation of Ti-Ni powders during mechanical alloying

The effect of milling energy on the phase evolution of mechanically alloyed Ti-Ni powders is reported. Alloys were produced by low-energy and high-energy mechanical alloying (LEMA and HEMA, respectively). Powders milled for different times were characterised by X-ray diffraction and scanning electron microscopy. The phase transformations of powders milled by LEMA and HEMA before amorphisation are presented. During LEMA, TiNi, TiNi3, Ti3Ni4, and Ti2Ni were formed at 50 and 100 h. At these times, the results were consistent with the Ti-Ni equilibrium phase diagram. Up to 7.27 wt% of TiNi with a crystallite size of 32.63 +/- 0.01 nm appeared at 50-75 h. During HEMA, iron contamination inhibited the formation of the TiNi phase at short milling times, and up to 47.9% of Fe0.2Ni4.8Ti5 was generated. These results indicate that amorphisation and heat treatment are not the only methods of promoting phase transformation in Ti-Ni alloys.