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 190rpm/4.0h 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/20MPa/1.0h preliminary, and then 950-1300°C/35MPa/1.0-2.5h 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/35MPa/1.5h. 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 1.5h exhibited a good combination property with the tensile strength and elongation of 620.53MPa, 7.44% at 650°C, respectively.