Research Projects - Hydrides

The formation of a face-centered cubic (FCC) titanium (Ti) phase is still one of the mysteries in this environmentally sensitive alloy family. We show in this project, how hydrides in Ti can be formed during sample preparation, reveal the underlying mechanisms and establish pathways to suppress or even eliminate the unexpected hydride formation. Hydride formation is mostly associated with the high diffusion rate and low solubility of hydrogen within the HCP matrix. Through plasmon loss electron energy loss spectroscopy (EELS) and atomic resolution imaging in combination with atom probe tomography (APT) we establish that predominantly TiH_X (x~50 at.%) forms in commercially pure Ti and show that focused ion beam preparation at cryogenic temperatures can suppress hydride formation. more

In this project, we explore the hydrogen-storage capabilities of quaternary refractory high-entropy alloys (RHEAs) showing transformation-induced plasticity (TRIP) by electro-chemical charging. The initially body-centered cubic (BCC) alloy can be partially transformed into the hexagonal close-packed (HCP) phase upon room temperature straining, allowing to adjust the HCP fraction by the pre-straining conditions. After electro-chemical charging a high fraction of compositionally complex face-centered cubic (FCC) hydrides form in the HCP phase. We employ atomic resolution imaging, electron energy loss spectroscopy (EELS) and in situ heating in the transmission electron microscope (TEM) to determine the hydride formation sequence, their stability and dissolution mechanisms. more