Microstructure and mechanical properties of Ti–45Al–5.5(Cr,Nb,B,Ta) alloy sintered at different SPS temperatures

Abstract

TiAl alloy bulk samples with the composition of Ti–45Al–5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti–45Al–5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti–45Al–5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.