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

Abstract

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 β-transus annealing was conducted at 1050 °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-β grains). Subsequently, the annealed furnace-cooled and water-quenched samples were aged at 540 °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 α+β, the aging treatment improved ductility and strength by inducing microstructural thickening of the α laths and reducing the β 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 α/α’ interfaces resulting from α’ 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 β-transus heat-treated Ti-6Al-4V alloy under different cooling conditions.

Effect of Heat Treatment and Hot Isostatic Pressing on the Corrosion Behavior of Ti6Al4 V Parts Produced by Electron Beam Melting Additive Manufacturing Technology

“…However, the peak belonging to the β phase was not distinctive after aging according to Figure . This removal of the retained β phase and the increase in α phase during the aging process aligns with findings in other studies. − The variation of the β-phase fraction is related to the diffusive transformation that occurs during aging. This process results in the decomposition of the retained β phase into a thermodynamically more stable microstructure, which contains a higher amount of α phase .…”

“…This removal of the retained β phase and the increase in α phase during the aging process aligns with findings in other studies. 42 − 44 The variation of the β-phase fraction is related to the diffusive transformation that occurs during aging. This process results in the decomposition of the retained β phase into a thermodynamically more stable microstructure, which contains a higher amount of α phase.…”

“…This process results in the decomposition of the retained β phase into a thermodynamically more stable microstructure, which contains a higher amount of α phase. 42 To observe the effect of aging on the microstructure, high-resolution SEM images were obtained from both the as-built aged (HT4) and HIP (HIP4) samples. These images are displayed in Figure 6 .…”

On the Degree of Plastic Strain during Laser Shock Peening of Ti-6Al-4V

“…It is also worth noting that the microstructure within the circled area in Figure 3b exhibited what appears to be either a Widmanstatten or a martensitic alpha microstructure. In titanium alloys, such microstructures are usually associated with high cooling rates; e.g., [30,31]. It is also interesting to note that the morphology of the Widmanstatten structure is somewhat similar to microstructural patterns sometimes ascribed to multiple twinning in several previous studies of laser-shock-peened Ti-6Al-4V (Supplementary Figure S2).…”

Experimental Investigation on Machinability of α/β Titanium Alloys with Different Microstructures

“…Solution treatment in the β-phase field followed by WQ at 1070 • C, and finally aging showed apparent martensitic transformation, where an almost complete martensitic α (α ) phase was obtained with some traces of α laths which increased in volume fraction due to martensite after the aging process (Figure 9c). According to Carrozza et al [30], this type of microstructure (martensite) is mainly formed by applying cooling rates greater than 410 • C/S from a temperature sufficiently higher than the martensitic start temperature. It is notable that the acicular α (α ) is much finer in the case of cooling from the β-phase field (Figure 9c,d).…”