Fatigue crack growth behavior for gas tungsten arc welded joint of TC2 titanium alloys sheets

Abstract

Gas tungsten arc welding (GTAW) is a most preferred welding method for titanium alloys. Due to severe inhomogeneity of welded joints resulting from welding heat input and stress concentration, the joints are prone to fatigue crack initiation, and the fatigue crack growth rate (FCGR) and direction have great variability. Thus, it is of great significance to master the fatigue crack growth (FCG) behavior for the evaluation of remaining life. The FCGR tests were performed in different zones of the TC2 titanium alloy joints welded by the GTAW, and the acceleration behavior of the FCG was investigated. The results show that the crack growth is accelerated prematurely at stable crack growth stage (stage II). The precracks in the weld zone (WZ) and heat affected zone (HAZ) present cross-regional growth during the acceleration process. The regions before and after the critical acceleration point correspond to stage IIa and stage IIb, respectively. The FCG life at the stage IIa accounts for 90% of the total life, and the stress intensity factor range at the critical acceleration point is much lower than that at the instability point. It is proposed that the critical acceleration point is taken as the remaining life evaluation point of the TC2 titanium alloy gas tungsten arc welded joint, and the crack should be limited to the stage IIa, where the FCGR decreases according to the base metal, WZ and HAZ. In addition, the control parameters and the critical criterion of the accelerated growth were proposed, which laid a foundation for the remaining life prediction of the TC2 titanium alloy structures welded by the GTAW.