Effect of Hydrogen Precharging on Mechanical and Electrochemical Properties of Pure Titanium

Abstract

The electrolytic hydrogen precharging process is used to analyze the influence of hydrogen on the microstructure, corrosion resistance, and mechanical properties of pure titanium. The results demonstrate that two types of titanium hydrides (δ‐TiHx and ϵ‐TiH2) are detected by electron backscatter diffraction (EBSD), and the volume fraction of titanium hydrides, the local strain caused by hydrogen precipitation, and the thickness of hydrides layer increase with the increase in precharging time. It is noteworthy that the formation of hydrides layer has a protective effect on general corrosion, but the local strain caused by hydrides precipitation leads to the destruction of corrosion resistance, as a result the corrosion resistance of pure titanium increases first and then decreases with the increase in hydrogen precharging time. Moreover, with the precipitation of hydrides, the fracture mode changes from ductile failure to duplex‐ and multimode failure, resulting in the decrease in ultimate tensile strength (UTS) and elongation. Therefore, the mechanical and electrochemical properties of the precharged samples first increase and then decrease with the increase in precharging time, reaching their optimum values at 10 h, and the critical precharging time is determined to be 75 h when comparing those properties with pure titanium.

Deciphering Hydrogen Embrittlement Mechanisms in Ti6Al4V Alloy: Role of Solute Hydrogen and Hydride Phase

“…The XRD patterns reveal that both hydrogen-charged and uncharged samples contain a majority of α phase with a small amount of β phase; however, small peaks of the HP (TiH 2 ) are only observed in the HP sample ( Figure 1 a). The TiH 2 has been demonstrated to be inducible through hydrogen charging and remains stable at RT [ 18 , 19 , 20 , 21 , 22 , 23 ]. Notably, the TiH 2 exhibits a body-centered tetragonal (BCT) crystal structure with lattice parameters of a = 0.312 nm and c = 0.418 nm (JCPDS-PDF 9-371) [ 24 ].…”

“…As a result, the precipitation of HP primarily occurs either at the α–β interface or GBs. The presence of a zero solution (observed in the EBSD maps in Figure 1 c) around the HP may be attributed to local strains within the HP, associated with volume expansion from the α phase-to-HP transformation [ 19 , 30 ]. Indeed, this transformation is reported to result in approximately an 18% volume expansion [ 11 ].…”