Effect of prior β-grain size on the hot deformation behavior of Ti-6Al-4V: coarse vs coarser

Abstract

The hot deformation behavior of extra low interstitial (ELI) grade Ti-6Al-4V with a transformed β-preform microstructure was studied in coarse (0.5 to 1 mm) and coarser (2 to 3 mm) (prior β) grained materials using hot compression testing in the temperature range of 750 to 1100°C and a strain rate range of 0.001 to 100 s⁻¹. Processing maps were developed on the basis of the flow stress data as a function of temperature and strain rate. The maps revealed that the domain of globularization of the lamellar structure and region of large grained superplasticity of β were not influenced by the prior β-grain size. However, the regimes of cracking at the prior β-grain boundaries occurring at lower temperatures and strain rates and the flow instability occurring at lower temperatures and higher strain rates were both wider for the coarse grained material than the coarser grained material. The β-instability regime, however, was more pronounced in the coarser grained material. From the hot workability viewpoint, the present results show that there is no remarkable benefit in refining the prior β-grain size. On the contrary, it will somewhat restrict the workability domain by widening the adjacent regimes, causing microstructural damage.