Characterisation of hydride formation in as-built and heat treated laser powder bed fused Ti-6Al-4V

Despite the increasing developments in laser powder bed fusion (L-PBF) of titanium, no relationships have been established yet on the hydride formation in the L-PBF titanium alloy Ti-6Al-4V. Nevertheless, insights in the development of titanium hydrides in this particular microstructure are e.g. useful for thermohydrogen processing and to avoid premature failure. Therefore, this work investigated the formation of titanium hydrides in as-built and heat treated L-PBF Ti-6Al-4V. Hydrogen was introduced via electrochemical hydrogen charging until hydrides precipitated. The evolution of titanium hydride formation was observed to be closely related to the microstructure, being associated to the hydrogen solubility and diffusivity in the different crystallographic phases. Investigation by scanning electron microscopy (SEM) and X-ray diffraction (XRD) demonstrated that parallelisms could be drawn to the hydride development in conventionally manufactured pure α and α-β titanium alloys, for as-built and heat treated L-PBF Ti-6Al-4V, respectively. Phase and texture analysis were performed with electron backscatter diffraction (EBSD) to identify the orientation relationships between the original microstructural phases and the formed δ hydrides. It was observed in heat treated L-PBF Ti-6Al-4V that intragranular δ hydrides inside the α grains precipitated according to the 0001α // 11̅1δ orientation relationship. On the other hand, hydrides at grain boundaries developed rather according to the 0001α // 001δ orientation relationship. Furthermore, nuances in hydrogen interaction are highlighted with respect to the conventionally manufactured counterparts.