Effect of Aging and Cooling Path on the Super β-Transus Heat-Treated Ti-6Al-4V Alloy Produced via Electron Beam Melting (EBM)

This work focuses on the effect of different heat treatments on the Ti-6Al-4V alloy processed by means of electron beam melting (EBM). Super beta-transus annealing was conducted at 1050 degrees C for 1 h on Ti-6Al-4V samples, considering two different cooling paths (furnace cooling and water quenching). This heat treatment induces microstructural recrystallization, thus reducing the anisotropy generated by the EBM process (columnar prior-beta grains). Subsequently, the annealed furnace-cooled and water-quenched samples were aged at 540 degrees C for 4 h. The results showed the influence of the aging treatment on the microstructure and the mechanical properties of the annealed EBM-produced Ti-6Al-4V. A comparison with the traditional processed heat-treated material was also conducted. In the furnace-cooled specimens consisting of lamellar alpha+beta, the aging treatment improved ductility and strength by inducing microstructural thickening of the alpha laths and reducing the beta fraction. The effect of the aging treatment was also more marked in the water-quenched samples, characterized by high tensile strengths but limited ductility due to the presence of martensite. In fact, the aging treatment was effective in the recovery of the ductility loss, maintaining high tensile strength properties due to the variation in the relative number of alpha/alpha' interfaces resulting from alpha' decomposition. This study, therefore, offers an in-depth investigation of the potential beneficial effects of the aging treatment on the microstructure and mechanical properties of the EBM-processed super beta-transus heat-treated Ti-6Al-4V alloy under different cooling conditions.