Microstructural evolution and mechanical properties of a high yttrium containing TiAl based alloy densified by spark plasma sintering

This study deals with the densification of a pre-alloyed TiAl powder with excessive yttrium addition by spark plasma sintering (SPS) technique. The gas-atomized Ti–43Al–5Nb–2V–1Y (at. %) powders were sintered at various temperatures between 1100 and 1250 °C, applying a uniaxial pressure of 40 MPa. The microstructures of pre-alloyed powders and SPSed TiAl alloy samples were analyzed by scanning and transmission electron microscopies. In addition, the compression tests of SPSed alloys was carried out at room temperature (RT). Attention is focused on the existing form and distribution of excess yttrium in the initial powders and the SPSed samples. The initial powder exhibits a dendrite structure, and yttrium-rich phases (YAl₂) are segregated along the interdendritic zone. After sintering, duplex, nearly lamellar (NL) and fully lamellar (FL) microstructures were obtained as a function of the sintering temperature. For duplex and NL microstructures, the YAl₂ phases are fine granular precipitates in homogeneous dispersion state. Conversely, stripe-like YAl₂ precipitates, which surround the α₂/γ lamellar colonies, emerged in the FL microstructures. Excessive sintering temperature leads to grain growth and serious segregation of the YAl₂ phases, and it deteriorates the mechanical properties of this alloy eventually.