Effect of microstructural heterogeneity on corrosion fatigue crack growth behavior of 60-mm thick-plate TC4 titanium alloy NG-GTAW welded joint

The microstructure, mechanical properties and corrosion fatigue crack growth behavior of 60-mm thick-plate TC4 titanium alloy narrow gap gas-tungsten arc welding (NG-GTAW) welded joints applied to the shell of the Jiaolong deep submersible were studied, and the effect of microstructural heterogeneity on the corrosion fatigue crack growth behavior was discussed. The results show that significant microstructure evolution occurred in the welded joint with acicular alpha' martensite coarsening and a random orientation distribution. The hardness and tensile strength distribution of the welded joints correspond to the difference in the microstructure, with a smaller size and more randomly oriented alpha' martensite providing superior strengthening effect. The acicular alpha' martensite of the weld metal (WM) has excellent resistance to crack growth compared to the alpha and beta phases of the base metal (BM). The degree of crack serration depends on the size and orientation distribution of the alpha grains and acicular alpha' martensite. As the stress increases, the fatigue resistance of BM may have a more serious deterioration trend compared with WM.