Microstructure and properties of a TiAl alloy prepared by mechanical milling and subsequent reactive sintering

A TiAl-based alloy with nominal composition of Ti-36 wt.% Al was prepared by a mechanical milling and reactive sintering route consisting of three basic steps: (1) mechanical milling of blended elemental Ti and Al powder mixture, (2) densification and consolidation of as-milled Ti/Al composite powder compact via warm extrusion, and (3) subsequent reactive sintering of as-extruded powder billet. The microstructure of the as-sintered TiAl alloy samples was observed by optical microscopy (OM) and transmission electron microscopy (TEM), respectively. The mechanical properties were measured by compression tests performed at room and elevated temperatures up to 800 °C. The results show that mechanical milling before reactive sintering is very effective in microstructure refining of reactively synthesized TiAl alloy. The TiAl alloy sintered from 1 h milled Ti/Al composite powders presented a homogeneous γ/(α₂ + γ) duplex microstructure with very fine grains of 5-10 μm and good mechanical properties. On the basis of microstructure observation and compressive stress-strain relationship, the deformation mechanism at different temperature was discussed.