Tensile Properties of Electrochemically Hydrogenated As-Built, Hot Isostatic Pressed and Heat-Treated Electron Beam Melted Ti–6Al–4V Alloys

Abstract

Only a few studies have reported the effects of electrochemical hydrogenation on the tensile mechanical properties of additively manufactured Ti–6Al–4V alloy, in all of them the alloy was processed by laser powder-bed fusion. Furthermore, the effects of either hot isostatic pressing (HIP) or heat treatment (HT) post-treatments on the mechanical properties were not reported. Here, the Young’s modulus, ultimate tensile stress, and uniform (homogeneous) strain of as-built electron beam melted (EBM) Ti–6Al–4V alloys were studied using small tensile specimens before and after electrochemical hydrogenation, as well as before and after secondary processes of HIP at 920 °C and HT at 1000 °C. The tensile properties of all hydrogenated alloys were significantly degraded compared to their non-hydrogenated counterparts. The yield stress could not be determined for all hydrogenated alloys, as failure occurred at a strain below 0.2% offset. The uniform strain of the hydrogenated alloys was less than 1%, compared to 1%–5% for the non-hydrogenated alloys. The fracture mode of the hydrogenated alloys after HIP and HT revealed cleavage fracture, indicating increased brittleness. In the as-built hydrogenated alloy, the fracture mode varied with location: brittle fracture occurred near the surface due to the formation of a hydride layer, while a more ductile fracture with dimples was observed below this layer.