Mutual effects of hydrogenation and deformation in Ti-Nb alloys

Abstract

Alloying of Ti-based alloys with hydrogen is used to modify the microstructure and improve mechanical properties. In this study, hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte at high fugacities. This research investigated in detail, by means of X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal desorption spectroscopy (TDS), and microhardness tests, the influence of hydrogen at high fugacities on the phase stability, desorption behavior, and microhardness in Ti-Nb (20 to 45 wt pct Nb) alloys before and after deformation. Hydrogenation of Ti-Nb was found to exhibit a significant effect on the phase stability as well as the microhardness of Ti-Nb alloys. Hydrogenation of Ti-20 wt pct Nb led to precipitation of (Ti,Nb)H x in the metastable a" matrix. In Ti-Nb alloys with 40 or 45 wt pct niobium, hydrogen stabilized the bcc β phase, but destabilized the hcp w phase. With increasing hydrogen content, an expansion of the lattice constant of the β phase occurred, followed by the formation of (Ti,Nb)H x . The influence of hydrogen on the microhardness of Ti-40 wt pct Nb and Ti-45 wt pct Nb shows only a minor effect, whereas Ti-20 wt pct Nb exhibits significant softening in response to hydrogen charging up to 3000 ppm. The TDS showed that deuterium desorption strongly depends on the niobium content and the deformation treatment prior to or after charging. The observed results should provide further insight on the mutual effects and the resulting micromechanism of hydrogenation and deformation in Ti-Nb alloys.