Enhancing the mechanical properties of electron beam welded TC17 titanium alloy joint by post-weld heat treatment

Supersaturated coarsening beta phase and submicron acicular martensitic alpha' phase originated by the high cooling rate during the welding process resulted in the electron beam welded TC17 titanium weldment to be poor in strength and ductility. Post-weld heat treatment was performed at 630 degrees C for 2 h to improve the mechanical properties of electron beam welded TC17 titanium alloy joint through modifying the microstructures of the weldment. Results showed that undesired alpha' martensites in the fusion zone and heat affected zone, which inhibited the mechanical response of the weldment, were completely eliminated. The supersaturated b phase with martensitic alpha' structure in the as-welded joint was recrystallized into alpha lamella with a width in nanoscale embedded in the beta matrix after the post-weld heat treatment, which conspicuously enhanced the mechanical performances of welded joints. Micro-hardness of the FZ presented to be more stable around HV410. Tensile strength was regained from 868 MPa to 1138 MPa, which was very closed to the raw material. Intrinsic metallic deficiency inducing fatigue failure of the as-welded joint was eliminated after the post-weld heat treatment accompanied with the fatigue strength enhancing from about 140 MPa of the as-welded joint to 240 MPa with an equal fatigue life of 10(7) cycles under the stress ratio of 0.1. (C) 2019 Elsevier B.V. All rights reserved.