Role of intracrystalline hydrogen on the ductility of dilute Ti-based alloys by first-principles calculations

Abstract

Titanium (Ti)-based alloy has been widely used as structural materials in deep-sea exploration with high pressure and reducing HCl environment. However, hydrogen (H) -induced destruction (hydrogen embrittlement) on Ti has been a problem in recent decades. Herein, H tends to occupy the octahedral interstice of Ti attributed to the lower defect formation energy, resulting in poor ductility of Ti. The elastic modulus is slightly enhanced originating from the strong electron localization and non-spherical electron cloud when H is dissolved, while the ductility is generally deteriorated in Ti35XH, especially for the alloying elements of 4th period. However, the ductility of Ti35NiH, Ti35ZrH and Ti35WH are significantly improved, that is, H makes the d orbit shift to the high energy band, increasing antibonding state and weakening bonding, which leads to the higher Poisson’s ratio and lower stacking fault energy (SFE). Therefore, Ni, Zr or W is a potential beneficial element that enhances or maintains the ductility of Ti at low concentration H.