The characteristics of load frequency of corrosion fatigue crack growth rate for Ti–6Al–4V alloys

摘要

Ti–6Al–4V alloys have been developed not only as structural materials for aerospace field but also as biomaterials for orthopedic surgery. As a crack growth mechanism under corrosive condition for Ti–6Al–4V alloys, mechanisms of anodic dissolvent chemical reaction and hydrogen embrittlement (HE) caused by chemical corrosive reaction have been proposed, however, the latter has not yet been clarified. In this study, corrosion fatigue (CF) crack growth tests under ringer and 3.5% NaCl solution were conducted for various type of Ti–6Al–4V alloys such as forging and casting with different values of yield stress. The characteristics of load frequency of corrosion fatigue crack growth rate (CFCGR) were investigated for these materials. It was found that various characteristics of load frequency for CFCGR appear depending on yield stress and concentration of NaCl solution. In some cases, it was found to show different characteristics of load frequency of CFCGR from those dominated by usual time dependent mechanism. In this research, a map of load frequency of CFCGR for these materials were established in terms of concentration of NaCl and yield stress. Finally some considerations were conducted which concerns the mechanisms of CFCGR such as anodic corrosive reaction and hydrogen embrittlement.