Microstructure and mechanical properties of Ti-22Al-25Nb alloy fabricated by elemental powder metallurgy

In order to better understand the relationship of processing-structure-mechanical properties of Ti-22Al-25Nb alloy fabricated by elemental powder metallurgy (EPM), the effects of sintering parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy were investigated. The blended powders with a nominal composition of Ti-22Al-25Nb (at%) obtained by 190 rpm/4.0 h milling under a protective argon atmosphere were used for the fabrication of Ti-22Al-25Nb alloy via hot-press sintering. The step sintering process was carried out at 630 °C/20 MPa/1.0 h preliminary, and then 950-1300 °C/35 MPa/1.0-2.5 h followed by furnace cooling. Microstructure were characterized using the scanning electron microscope (SEM) and transmission electron microscopy (TEM). Tensile tests were performed at room temperature and 650 °C, respectively. Results showed that the typical lamellar microstructure consisting of α2, O and B2 phases were observed in the Ti-22Al-25Nb alloys sintered at 1250 °C/35 MPa/1.5 h. Moreover, the forming mechanism of O (orthorhombic Ti2AlNb) phase and reactive mechanism were analyzed. The elongations of the sintered Ti-22Al-25Nb alloys were less than 5.09%, indicating the bad ductility at room temperature. However, The Ti-22Al-25Nb alloy sintered at 1250 °C for 1.5 h exhibited a good combination property with the tensile strength and elongation of 620.53 MPa, 7.44% at 650 °C, respectively.