Experiment and Numerical Simulation of Ti-22Al-25Nb Alloy Sheet by Gas Bulging

Abstract:

The hot formability of Ti-22Al-25Nb alloy sheet at elevated temperatures was studied through the gas bulging experiments and numerical simulation. The distributions of bulging shell shape and wall thickness at 930 and 970 °C were analyzed. The microstructure and mechanical properties of the bulging part were discussed. Results show that the bulging shell is close to the spherical surface in the initial bulging stage, and it gradually becomes ellipsoid with increasing the bulging height. At 930 and 970 °C, the final bulging height reaches 46.25 and 49.85 mm, and the curvature radius of shell top reaches 49.33 and 49.19 mm, respectively. The wall thickness of bulging part is inhomogeneous: it gradually decreases from the bottom region to the top region. The deformation temperature strongly affects the shape of bulging part: the partial bulging shape is more inhomogeneous at low temperature of 930 °C. Under the same bulging height, the curvature radius of bulging is lower and the thinning ratio is higher at 930 °C. In addition, the O phase is precipitated and spheroidized during bulging at 930 °C, which causes the generation of O type and V type cavities and the reduction in microhardness. However, the microstructure is uniformly distributed after bulging at 970 °C. O phase is precipitated during the cooling process in lamellar morphology, which strengthens the bulging part.

Key words:Ti₂AlNb;gas bulging;hot formability;microstructure