Accelerating globularization in additively manufactured Ti-6Al-4V by exploiting martensitic laths

Abstract

Ti-6Al-4V alloy has limitations in terms of globularization when using additive manufacturing (AM), which requires a final forging step. To optimize this approach, this study investigated the effect of processing variables on the dynamic/static globularization of AM-processed Ti-6Al-4V alloy. Eight double-cone specimens were prepared with different processing variables such as effective strain, solution treatment, hot-forging temperature, and subsequent annealing. Microstructural evolutions were quantitatively characterized to interpret the kinetics of globularization based on the aforementioned variables. In particular, the combination of solution treatment, low-temperature (1073 K) forging, and subsequent annealing significantly accelerated the overall globularization. Such an accelerating effect stemmed from the reduced path for boundary splitting in fine α′ martensitic laths, which was induced via solution treatment. This accelerating effect disappeared at a high temperature (1223 K), which implies the necessity of optimizing the thermomechanical route to exploit martensitic laths.

Keywords

• Additive manufacturing
• Ti-6Al-4V
• Martensite
• Dynamic globularization
• Static recrystallization