Microstructure and mechanical properties of Ti2AlNb cup-shaped part prepared by hot gas forming: determining forming temperature, strain rate, and heat treatment

Abstract

In aerospace industry, Ti2AlNb-alloy has attracted considerable attentions as a potential material to long-time service at 650–750 °C. In order to study the deformation of the Ti2AlNb component, the cup-shaped specimens were bulged by hot gas forming tests at 985, 950, 930 °C with strain rate of 0.001 s−1 and 970 °C with strain rate of 0.1, 0.01, and 0.001 s−1, respectively. The effects of forming temperature, strain rate, and heat treatment on strain distribution, microstructure, and mechanical property of the Ti2AlNb parts were investigated by thickness measurement, BSE image, EBSD and TEM, and hot tensile tests. With a low forming temperature (930 and 950 °C) or a high strain rate (0.1 and 0.01s-1), the strength of the deformed part is relatively low because of the damage and dislocation. Meanwhile, the mechanical properties of the deformed parts were affected by the heat treatment schemes because of the different O-phase organization. The uniform microstructure with fine lath O-phase grains, equiaxed α2, and matrix B2 phase were obtained by hot gas forming at 970 °C with strain rate of 0.001 s−1 and 2-h heat treatment at 820 °C, presenting enhanced ductility and strengthening behavior, i.e., elongation is 3.2% and yield strength is 787.3 MPa.