Effects of cathodic charging and subsequent solution treating parameters on the hydrogen redistribution and surface hardening of Ti-6Al-4V alloy

Sheet specimens of Ti-6Al-4V alloy (Ti-64) were processed according to the designed cyclic hydrogenating-solution treating parameters to see the effect of various treatments on microstructural change, hydrogen redistribution and surface hardening. The variation of microstructure, hydrogen distribution and surface hardness was analyzed by employing X-ray diffractometry (XRD), glow discharge optical spectrometry (GDOS) and microhardness tester. Cathodic charging combined the subsequent solution heat treating to cause significant microstructural changes of Ti-64. Hydrogen and oxygen absorbed during cathodic charging were outgassed spontaneously in the light of thermodynamic equilibrium to bring about the redistribution. The main hardening effect found in this study was derived from hydrogen uptake. The fluctuation in surface hardness of hydrogenated Ti-64 was the competitive result between hydrogenation hardening and thermal annealing softening.