Influence of interstitial carbon on the formation of monohydride and dihydride of Ti25V35Cr40 alloys

Abstract

The presence of interstitial carbon atoms was found to affect the hydrogenation properties of Ti25V35Cr40Cx (x = 0, 0.1, and 0.5) alloys over the range T = 30–300 °C. Heat treatment at T = 1200 °C was used to homogenize the distribution of carbon atoms throughout the specimens. X-ray diffraction, P–C isotherm curves, and thermodynamic measurements, including van't Hoff plots and in-situ temperature-programmed desorption spectra, were used to study the destabilization of the β-phase monohydride and γ-phase dihydride in annealed Ti25V35Cr40Cx as a result of the presence of interstitial carbon atoms. The experimental results showed that the interstitial carbon atoms introduced both obstacles and carbon-induced microstrain into the structure, which significantly destabilized the γ-phase dihydrides to enhance the corresponding plateau pressures at T = 30–80 °C. On the other hand, destabilization of the β-phase monohydride was less pronounced in the presence of interstitial C atoms at T = 150–300 °C. This effect was ascribed to a lower H content in the saturated β-phase monohydrides as compared with the saturated γ-phase dihydrides, as well as microstrain relaxation at higher temperatures.