Effects of the heterogeneity in the electron beam welded joint on fatigue crack growth in Ti–6Al–4V alloy

The heterogeneity of electron beam (EB)-welded joints in thick Ti–6Al–4V alloy plates is defined and described. The microstructure, hardness, and fatigue crack growth rate (FCGR) in the fuse zone (FZ) and the heat-affected zone (HAZ) of thick Ti–6Al–4V alloy EB-welded joint are studied using a new testing and interception method. The fatigue fractographs, crack growth paths and the microscopic deformation are observed through scanning and transmission electron microscopy. The effect mechanism of heterogeneity in the electron beam weld joint to FCGRs is discussed. The results reveal that FCGR is higher in the HAZ than in the FZ, mainly because of the effect of heterogeneity I of the welded joint. Heterogeneity II increases from the top to the root of the welding seam while the size of the α′ phase decreases. Consequently, FCGR is higher at the root of the welding seam. Heterogeneity in the joint is found to greatly influence the FCGR.