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

Abstract

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.