Effects of hydrogen exposure on the mechanical and tribological properties of α-titanium surfaces

Abstract The influence of electrolytic hydrogenation on the mechanical properties of the near-surface microstructures of titanium and the resulting tribological behavior (scratch tests and reciprocating ball-on-plane tests) was investigated. Hardening effects of hydrogenation were revealed by nano-indentation methods. Additional quantitative characteristics, such as micro-indentation hardness, Young's modulus, and the work of elastic and plastic deformation, have also been determined. Plastic deformation of surface micro-asperities dominated during the sliding friction of non-hydrogenated titanium. By contrast, brittle fracture and crack formation were observed on hydrogenated surfaces. In a limited number of experiments, the coefficient of friction was reduced by as much as a factor of three after hydrogenation. A mechanism by which hydrogen affects the tribological behavior of titanium has been proposed. Hydrogen, localized in the dislocation cores, blocks their movement, which leads to hardening of titanium and a reduction in its ductility. During sliding, the periodic external and internal stresses overlap at the contact points, and that leads to micro-cracking and brittle fracture. Evidence for this mechanism remains to be demonstrated in future work.