Effect of post-welding heat treatment on microstructure and properties of electron beam welding joint of new high-strength TB18 titanium alloy

This paper investigates the influence of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of an 80-mm thick TB18 electron beam–welded (EBW) joint. The average tensile strength of TB18 base metal (BM) is 1328 MPa, while the tensile strength of as-welded joints is 736 MPa, which is only 55.3% of the BM. After post-welding heat treatment (PWHT), the tensile strength of the joint is slightly higher than that of the BM, which is 1341 MPa. The fracture morphology of the BM and two kinds of joints are analyzed. There are a lot of dimples in the tensile fracture of the BM and as-welded joint, which are ductile fractures, while the tensile fracture morphology of the PWHT joint is mainly composed of dimples and cleavage planes, which are quasi-cleavage fractures. The microhardness of the weld metal (WM) of the as-welded joint is significantly lower than that of the BM, while the microhardness of the PWHT joint is close to that of the BM. There are obvious differences in the microstructure of the WM between the two kinds of joints. The WM of the as-welded joint is mainly composed of large β columnar crystals, while a large number of fine flaky α′ phases are precipitated in the WM of the PWHT joint.