HYDROGEN EMBRITTLEMENT AND FRACTURE-TOUGHNESS OF A TITANIUM-ALLOY WITH SURFACE MODIFICATION BY HARD COATINGS

The effect of hydrogen embrittlement on the fracture toughness of a ti tanium alloy with different surface modifications was investigated. Di sk-shaped compact-tension specimens were first coated with different h ard films and then hydrogen charged by an electrochemical method. Glow discharge optical spectrometry (GDOS), scanning electron microscopy ( SEM), and x-ray diffractometry (XRD) were applied to analyze the surfa ce characteristics. The results revealed that fracture toughness of th e as-received titanium alloy decreased with the increase of hydrogen c harging time. Fracture toughness of the alloy after plasma nitriding o r ion implantation, which produced a TiNx layer, decreased as well, bu t to a lesser extent after cathodic charging. The best result obtained was for the alloy coated with a CrN film where fracture toughness was sustained even after hydrogen charging for 144 h. Obviously, the CrN film acted as a better barrier to retard hydrogen permeation, but it w as at the sacrifice of the CrN film itself.