Titanium (Ti) and Ti-based alloys possess superior combined physical and mechanical properties in addition to strong corrosion resistance, which make them outstanding materials for a variety of structural and functional applications. There is a major concern associated with hydrogen or hydride phases residing in the Ti alloy matrix, as their existence has led to issues with environmentally assisted cracking, including hydrogen embrittlement (HE) and hydride-induced cracking (HIC). A major local microstructural feature that is sensitive to embrittlement and cracking is grain boundary due to low activation barrier for hydrogen/hydride uptake relative to grain interior. The grain size, which determines the total surface and volume fractions of grain boundary on the surface or in the bulk material, plays a critical role in hydrogen/hydride uptake, accumulation, and strain distribution that can potentially crack the materials. In this work, we investigated the grain size effect on hydrogen trapping, hydrogen/hydride distribution, and associated strain distribution in ultra-pure alpha Ti metal via multiscale characterization and computer simulations. Specifically, we made a suite of samples that have varying grain sizes spanning ~3 orders of magnitude from micrometer to millimeter in dimensions in ultra-pure alpha Ti (99.999%) from thermal post processing treatment and H-charged them under elevated temperature and pressure environment to induce hydrogen pickup and hdyrides formation. The H-charged samples are assessed using a suite of characterization tools including SEM/TEM-EBSD, SIMS, and in particular non-destructive neutron diffraction to assess site-specific microstructural features, hydrogen/hydride content and crystal lattice strain changes. Through the integration of experimental and simulation results, the grain size effect on hydrogen/hydride and strain distribution will be revealed.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.