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 Fe_0.2Ni_4.8Ti₅ was generated. These results indicate that amorphisation and heat treatment are not the only methods of promoting phase transformation in Ti–Ni alloys.