THERMAL HYDROGEN DESORPTION SPECTROSCOPY OF HYDRIDES FORMED IN THE SURFACE-LAYER OF AN ELECTROCHEMICALLY TREATED TIAL BASED ALLOY

Decomposition of hydrides formed in the surface layer of a TiAl-based alloy by an electrochemical treatment in sulfuric acid solution was st udied by thermal desorption spectroscopy (TDS) combined with quadrupol e mass spectroscopy (QMS), and X-ray diffractometry (XRD). Two peaks i n the TDS curve and the results of QMS supported the presence of two h ydrides in the alloy which was suggested by a previous study. XRD show ed that the tetragonal hydride decomposed at 400 K corresponds to the first peak in TDS curve and the hexagonal hydride decomposed at 500 K corresponds to the second peak. The lattice parameters of the tetragon al hydride are a=0.455 nm and c=0.463 nm and these of the hexagonal hy dride are a=0.523 nm and c=0.448 nm. The reason why two hydrides were formed is discussed.