Mechanical Behavior of Hot-Rolled and Direct Metal Laser-Sintered Ti6Al4V Alloy in the Presence of Hydrogen

Abstract

The dual-phase titanium alloys like Ti6Al4V show a high susceptibility toward hydrogen embrittlement (HE) due to the formation of bulk hydrides caused by the rapid diffusion of hydrogen through the BCC β-phase. The present study aims to understand the role of hydrogen in the underlying deformation micromechanisms and susceptibility toward HE for different microstructures of Ti6Al4V. To this end, three different microstructures─hot-rolled (HR), direct metal laser-sintered (DMLS), and annealed–direct metal laser-sintered samples at 850 °C for 2 h (HT DMLS)─were electrochemically hydrogen-charged. X-ray diffraction results indicate the formation of titanium hydride after hydrogen charging. Tensile tests were performed on the uncharged and hydrogen-charged samples at room temperature with a nominal strain rate of 10–3s–1. The tensile results exhibit an increase in yield strength, ultimate tensile strength, and reduced ductility in hydrogen-charged HR Ti6Al4V samples, whereas yield strength, ultimate tensile strength, and ductility were reduced for hydrogen-charged DMLS and HT DMLS samples. A localized hydrogen-affected zone in HR Ti6Al4V and a uniform hydrogen-affected zone in DMLS and HT DMLS were observed in fractography. The intragranular kernel average misorientation (KAM) parameter from electron backscatter diffraction (EBSD) showed the strain localization near the interphase boundaries due to restricted slip transfer between two phases, which reduces the ductility in the presence of hydrogen for all three microstructures.