Reactive extrusion synthesis of mechanically activated Ti–50Ni powders

In the present study, an alternative approach to the synthesis of TiNi alloys through powder metallurgy was successfully conducted by mechanically activated reactive extrusion synthesis (MARES) using elemental powders. The production of dense bodies was essentially dependent on the amount of intermetallic phases formed prior to reactive extrusion and on the densification temperature. The mechanically activated powders yielded a well controlled synthetic reaction during heating up to 900 °C with formation of multiphase products. This was possible due to the powder structure developed during mechanical activation. The best densified products were obtained at 700 °C although without a complete conversion into NiTi phase. More homogeneous microstructures and an effective reduction in the amount of secondary intermetallic phases were achieved after heat treatment at 950 °C/24 h followed by water quenching, yielding TiNi as the predominant phase, a relative density of 97%, and a Vickers micro-hardness of 682 H_V.