Effect of hydrogen on phase and microstructure of Ti600 alloy

Effects of hydrogen on microstructure characteristics and precipitation behavior have been investigated in Ti600 alloy hydrogenated at 750 degrees C. Due to the precipitation of delta hydride and alpha '' martensite, X-ray diffraction (XRD) peaks of alpha phase shifted to lower angles and became broadened. XRD data showed that the addition of hydrogen expanded crystal lattice of alpha phase and lattice volume increased linearly in the range of 0 < C-H < 0.792 wt%. XRD, scanning electron microscopy, and transmission electron microscopy analysis revealed precipitation behavior of secondary alpha lamellar, alpha '' martensite and delta hydride. Compared to as-received one, microstructure of hydrogenated Ti600 alloy changed obviously. Equiaxed alpha phase decreased and even vanished with hydrogen contents increasing. Parallel fine lamellar structure appeared and the colonies were constructed by different orientation. Micro-hardness of hydrogenated Ti600 alloy increased with the increase of hydrogen concentration, and it was considered that interstitial solution strengthening, precipitation of delta hydride, and generation of defects were the major factors.