Effect of weld repair on microstructure and mechanical properties of laser additive manufactured Ti-55511 alloy

Gas tungsten arc welding was used to repair the laser additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy with a subsequent triplex annealing treatment. The tensile properties of heat treated specimens containing of different proportions of weld zone were designed to evaluate the influence of weld zone on tensile properties of the alloy. Microstructures, microhardness and tensile tests were performed to study the mechanical properties and fracture behaviors of the specimens. Results show that dissolved oxygen in the weld zone has a strong influence on increasing the number of α phase nucleation sites that can lead to different α_p morphologies in the base metal and weld zone. These different α_p can lead to distinct microstructures after triplex annealing treatment but with similar α volume fractions. Besides, plasticity deterioration of the repaired tensile specimens is mainly attributed to the formation of columnar grain boundary α phases in the weld zone which are considered to be the earliest nucleation sites of microcracks and confirmed by in situ tensile test. With the increase of WZ proportions in the cross section of tensile specimens, the plasticity of the alloy gradually decreases.