An Investigation of Phase Transformation in (Ti‐6Al‐4V)‐H Using in Situ High‐Energy Synchrotron XRD

Abstract

Hydrogen has been investigated for decades as a temporary alloying element to refine the microstructure of Ti-6Al-4V in thermohydrogen process (THP), and is now being used in a novel powder metallurgy method, hydrogen sintering and phase transformations (HSPT). The phase transformations and the phase diagram of (Ti-6Al-4V)-H are, however, still not fully understood or well established, to date. In the present work, a pseudo-binary phase diagram of (Ti-6Al-4V)-H was determined by using in situ synchrotron XRD, combined with TGA/DSC techniques. Aided by this phase diagram, the series of phase transformations exhibited during the entire HSPT process were investigated. The microstructural refinement was found to be the result of the precipitation of ultra-fine / 2 within coarse grains, as well as from a eutectoid transformation of + at approximately 200 ºC. These results provide evidence of the mechanism of microstructural refinement of not only HSPT, but also during THP, and may have relevance to hydrogenation-dehydrogenation (HDH) powder production technologies.