Effect of electrochemical hydrogen charging on defect structure in titanium

Abstract

The influence of hydrogen on defect structure in pure titanium was systemically investigated using X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS). The results showed that hydrogen damage was related to hydrogen concentration, and PAS provided a new idea for the study in the formation of hydride and open volume defects. XRD results showed that two types of titanium hydrides were observed in hydrogen-charged samples, i.e., δ-TiHx and ε-TiH2, and the degree of lattice expansion and the content of hydride increased with hydrogen content. The variation of the S parameter and W parameter indicated that a great deal of vacancy-type defects formed during electrochemical hydrogen charging, and hydrogen atoms could combine with vacancy to form a certain amount of hydrogen-vacancy complexes (HnVm), meanwhile, the hydrogen damage varied significantly with depth. The effective open volume of vacancy-type defect increased with hydrogen charging concentration, and hydrogen-vacancy cluster transformed into HnVm (n < m) cluster, vacancy defects were gradually dominated. In addition, According to the different annihilation environment of positron in titanium hydrides and hydrogen-vacancy complexes, the existence of titanium hydrides and the existing form of hydrogen in defect could be identified in Doppler broadening spectroscopy (CDB). This provided a new way to identify the formation of hydrides and to detect the existing form of low concentration hydrogen in samples.