Effect of Solution Temperature on Microstructure and Properties of Ti6Al4V by Laser-Directed Energy Deposition

Solution-aging treatment of Ti6Al4V titanium alloy by laser-directed energy deposition (LDED) is an efficient way to enhance their microstructure and properties, as well as to achieve their structural stability. The present work is aimed at investigating the microstructure and mechanical characteristics of the as-deposited and solution-aged LDEDed Ti6Al4V. The solution treatment is carried out within the temperature ranges of the ( α + β ) dual-phase and β single-phase regions. In the first case, the solution-aged LDEDed Ti6Al4V possesses a basketweave structure. With the increase in solution temperature, the coarsening (thickening) of the primary α ( α I ) phases in the basketweave organization is evident. Moreover, the content of ( α + β ) microstructures between the α I phases gradually increases, and the density of secondary reticular and punctate β ( β II ) phases within the α I phases becomes higher, as well. In turn, the α I phases from the initial β phase grain boundaries gradually disappear. In the second case, the structural modifications with increasing solution temperature of LDEDed Ti6Al4V are found to be mainly the same as in the above dual-phase region. The only difference is that Widmanstatten structure is formed, the α I phases of the lamellar structure become more apparent, and the primary α I phases at the grain boundaries of the initial β phases gradually increase. Besides, an increase in the solution temperature causes the tensile strength and the yield strength of Ti6Al4V to increase. On the contrary, the elongation and reduction of the area gradually decrease, but both are plastic fractures. Moreover, under 910 °C/1 h/WQ + 550 °C/4 h/AC and 950 °C/1 h/WQ + 550 °C/4 h/AC solution-aging conditions, the tensile properties of the alloy are found to be basically equivalent to the standard of forgings. However, the sample’s mechanical properties after solution-aging treatment of the β single-phase region did not fully meet the requirements of forging standard.