The influence of gaseous hydrogen charging on the microstructural and mechanical behavior of electron beam melted and wrought Ti–6Al–4V alloys using the small punch test

Abstract

The influence of gaseous hydrogen charging at 600 °C on the microstructure and mechanical behavior of wrought and Electron Beam Melted (EBM) Ti–6Al–4V alloys was investigated for hydrogen contents between 0.14 and 1.0 wt%. The small punch test (SPT) technique was used to characterize the mechanical behavior of all specimens. Both EBM and wrought alloys containing ∼6 wt% β and similar impurity levels showed similar phase content and mechanical property changes at all hydrogen contents, regardless of their original microstructural differences. This similarity can be explained by the high hydrogen diffusivity at the high temperature at which gaseous charging was carried out, and is in contrast to previous reports where EBM Ti–6Al–4V was found to be more sensitive to hydrogen embrittlement due to low-temperature electrochemical charging. After hydrogenation, αH and βH solid solutions were formed. The quantity of the αH phase reduced gradually with hydrogen content, while forming βH, α2, and hydrides. It was found that βH saturated at 0.27 wt% hydrogen content. Both alloys demonstrated relatively high strength and ductility up to hydrogen content of 0.2 wt%, i.e. below the βH saturation concentration. Above the βH saturation concentration, the mechanical properties of the maximum load (Pmax), deflection at maximum load (δmax), and absorbed energy (E), degraded significantly due to hydride formation.