Causes of abnormal double shear fracture of TC4 titanium alloy high-lock bolt

A TC4 titanium alloy high-lock bolt was abnormally fractured during the double shear test.Through macroscopic observation,microstructure observation,fracture analysis and double shear test,the reasons for the abnormal double shear fracture of high-lock bolt were analyzed.The results showed that during the heat treatment process of high-lock bolt,they were not taken out in time in the vacuum furnace,so that the bolt were kept warm in the furnace for a long time,resulting in a thicker surface contamination layer and micro cracks.It could be seen from the processing technology of high-lock bolt that in the finishing process after heat treatment,the small machining allowance led to incomplete removal of the bolt surface contamination layer.During double shear test,the micro cracks spreaded rapidly along the brittle and hard,surface contamination layer under the action of bending moment until the bolt fractured.