The Influence of Temporary Alloying of Hydrogen on the Microstructure and Superplasticity of Ti-6Al-4V Alloy

摘要

A fine, equiaxed duplex microstructure, high temperature and low strain rate are essential requirements for superplastic forming (SPF). However, considerable property degeneration is unavoidable when grain growth occurs during high temperature forming. In this study, temporary alloying of the hydrogen treatment was conducted to reduce the forming temperature and, thus, improve the superplastic property at lower temperatures; in addition, the influence of hydrogen on the microstructure was also investigated. The results indicate that two different procedures using hydrogen can be employed to modify microstructure changes: (1) consecutive slow changes in the microstructure and gradual modification in the alpha-beta volume fraction at low temperatures, and (2) at higher hydrogenation temperatures, an abrupt change in the microstructure and a new alpha-beta volume fraction achieved by using a fast re-equilibrium process. For superplastic forming, considerable improvement in the forming height is obtained through a small addition of hydrogen into the as-received material at the same forming temperature using a proper hydrogenation temperature/hydrogen concentration combination.