Microstructures and deformation mechanisms of a G4 TiAl alloy produced by spark plasma sintering

TiAl alloys are prepared by spark plasma sintering (SPS) using a pre-alloyed powder with the so-called G4 composition (Ti51Al47Re1W1Si0.2). SPS densifications are conducted using short and classical cycles, with various dwell temperatures. The microstructure of the products is studied by scanning and transmission electron microscopy. In particular, constituent phases, grain size, precipitates and local chemical composition are determined. A double phase γ+α2 microstructure containing B2 precipitates is found in a large range of sintering temperatures. Mechanical properties at RT and creep strength at 700°C/300MPa are measured. No significant improvement of the mechanical properties is obtained with respect to those of SPS-TiAl alloys previously sintered. A study of the deformation mechanisms and the effect of the microstructure on these mechanisms is performed. Hence, the strong effect of microstructural heterogeneities from the initial powder is demonstrated.