Two types of hydrides formed in gamma phase of Ti-47 mol%Al alloy by electrochemical treatment in sulfuric acid

Metal hydride (MH) formation in a Ti-47 mol% Al (47Al) alloy with the y + a lpha (2) lamellar structure through electrochemical treatment in sulfuric a cid has been studied by X-ray diffractometry (XRD), thermal desorption spec trometry (TDS) combined with quadrupole mass spectrometry (QMS) and SEM. It has been shown for the y phase that cathodic polarization (CP) makes onl y one type of MH having a tetragonal structure (MHTET) Of about 10 Crm thic k at the reaction surface. An addition of anodic polarization (AP) after CP makes another type of MH having a hexagonal structure (MHHEX) of 1-2 mum t hick along the reaction surface. On the other hand, MH with HCP structure ( MHHCP) is formed in the alpha (2) phase by either CP or CP+AP. Each hydride gives an individual peak in TDS and QMS curves. The peaks of MHTET, MHHEX and MHHCP are located at around 200, 400, 600 degreesC, respectively. Heati ng in vacuum to the temperature above each peak decomposes the hydride corr esponding to the peak. The preferential dissolution of Al atom from the y phase of Al-47 alloy by anodic reaction makes compositional change and lattice defects near the rea ction surface, and it is considered that MHHEX is formed by movement of hyd rogen atoms to the defects. The fact that the formation of two types of MH in the gamma phase of 47Al alloy by CP+AP is strongly suggests the possibil ity that two kinds of MH are formed in the gamma single phase alloy.