Microstructure and elevated-temperature mechanical properties of in situ Ti2AlNb-reinforced TiAl-matrix composite prepared by powder metallurgy

Abstract

An in situ Ti2AlNb-reinforced Ti–45Al–5Nb–0.3 W-based intermetallic composite was prepared using 2 vol. % Nb powder and TiAl pre-alloy powder. The microstructure evolution and elevated-temperature mechanical properties of the Ti2AlNb/TiAl composite were investigated. The results show that during the hot isostatic pressing (HIP) process, Nb diffused into the TiAl matrix, and formed Nb-rich particles in which an Nb-rich-region and the coarse rod-like Ti2AlNb phase existed. After hot extrusion, the Nb-rich particles elongated along the direction of extrusion. Further, the mean diameter of the Ti2AlNb phase regions decreased, and the Ti2AlNb content increased. After heat treatment at 1280 °C for 1 h, the rod-like Ti2AlNb phase regions in the extruded specimen transformed into needle-like and fine lath-like structures, and the proportion of Ti2AlNb in the Nb-rich-regions increased. The extruded Ti2AlNb/TiAl specimen shows a high tensile elongation (TE), and the heat-treated specimen shows a high yield strength (YS) and ultimate tensile strength (UTS) at the test temperatures of 750 °C–900 °C. In particular, the extruded specimen shows excellent strength–ductility product (UTS × TE) values of 38.8 GPa% and 46.9 GPa% at 800 °C and 850 °C, respectively. The high toughness of TiAl intermetallic composites was because of the fibrous tough Nb-rich-regions that contained the fine Ti2AlNb phase.