Microstructure and mechanical properties of Ti-22Al-25Nb alloy fabricated by vacuum hot pressing sintering

A study has been undertaken to verify the feasibility of using a powder metallurgy (P/M) approach to fabricate Ti-22Al-25Nb alloys. Pre-alloyed powders with a nominal composition of Ti-22Al-25Nb (at%) obtained by argon atomization were sieved to the spherical size less than 180 μm and used for the fabrication of P/M Ti-22Al-25Nb alloys via hot pressing in vacuum. Vacuum hot pressing sintering was carried out in a temperature range of 950-1200 °C with a pressure of 35 MPa for 1 h followed by furnace cooling. Microstructure and phase composition examinations of the as-atomized powders and hot pressed (HP׳ed) samples were conducted by applying optical microscopy, back-scatter electron imaging and X-ray diffraction analysis. Tensile tests were studied at room temperature and 650 °C, respectively. The results showed that all HP׳ed samples were composed of coarse equiaxed B2 grains, fine lamellar O phase inside the B2 grains, and some α2 along B2 grain boundaries. The elongations of HP׳ed samples were less than 3.95%, indicating the bad ductility at room temperature. However, the elongations were improved as the tensile temperature increased to 650 °C. The sample sintered at 1050 °C exhibited a better ductility with the elongation of 7.97% at 650 °C than that of other samples.