Physical properties of hydrogen in TiVMnCr bcc alloys as deduced from hydrogen absorption/desorption and mechanical spectroscopy experiments

The hydrogen absorption/desorption properties of the Ti40VxMn(50-x)Cr10 alloys (x = 32 and 36) have been investigated between 78 and 201 degrees C. The partial molar enthalpy Delta H of the di-hydride formation has been found to be -52 +/- 7 kJ/mol and the desorption plateau pressure turned out to be rather low (<= 2 bar) even at a temperature as high as 183 degrees C. Internal friction and Young's modulus measurements between the ambient and liquid nitrogen temperatures revealed the existence of the H-Snoek effect, whose relaxation strength and width at half peak height were found to increase not linearly with hydrogen content. This behaviour is due to the occupancy by hydrogen of different types of tetrahedral interstitial sites. The experimental results suggest that the various transformation sequences observed on hydrogen charging in these bcc solid solution alloys is primarily determined by hydrogen-hydrogen repulsive interactions. A qualitative model is proposed to account for these transformation sequences. (C) 2007 Elsevier B.V. All rights reserved.