Hot deformation behavior and dynamic recrystallization of melt hydrogenated Ti-6Al-4V alloy

Abstract

The effect of hydrogen on hot deformation behavior of Ti-6Al-4V alloy was investigated. Ti-6Al-4V alloy was hydrogenated by melting alloy in gas mixture of hydrogen and argon (melt hydrogenation). Experimental results of hot compression at same strain rate showed hydrogen decreased flow stress at higher deforming temperature, which was attributed to hydrogen induced dislocation movement and dynamic recrystallization (DRX). At lower temperature, peak stress firstly decreased and then increased with increasing hydrogen content. Hydrogen decreased the peak stress and improved the hot workability of alloy deformed at same temperature and different strain rates. Microstructure observation of as deformed alloy indicated hydrogen promoted DRX on both α and β phase, and encouraged the decomposition of residual lamella. Electron back-scattered diffraction results indicated that hydrogen mainly encouraged discontinues DRX and decreased the dislocation density in α phase. Compared to unhydrogenated alloy, when hydrogen content was 5.31 × 10−2 wt.%, volume fraction of DRX increased from 42% to 53% and 41.8%–72.1% at strain rate of 0.01 and 0.001 s−1, respectively.