Constitutive and microstructural characteristics of Ti-5Al-2.5Sn alloy during isothermal and non-isothermal multi-stage hot deformation across different phase regions

The flow behaviors and microstructural evolutions during multi-stage hot deformation are essential aspects in the processing of high performance titanium alloys. In the present work, both isothermal multi-stage deformation (IMD) and non-isothermal multi-stage deformation (NMD) over alpha + beta and single beta phase regions were employed to study the constitutive behaviors and microstructural evolutions of a near-alpha Ti-5Al-2.5Sn alloy. The results showed that the flow stress, restoration fraction in alpha + beta phase region of NMD were lower than that of IMD, because that the predominant lamellar microstructures formed during NMD increased alpha/beta boundaries and thereby promoted grain boundaries gliding. In beta phase region, the flow behaviors showed slight differences with temperature and deformation passes during both IMD and NMD processes. Clear transitions were observed from the mean flow stress between different phase regions during NMD. In addition, an obvious alpha + beta ->beta dynamic phase transformation occurred during deformation at 990 degrees C, which was identified to be a displacive nucleation and diffusion-controlled growth process. In addition, numerous FCC-Ti precipitations were observed during IMD at 960 degrees C and strain rate of 1 s(-1) with the orientation relationship of (0 0 0 1)(HCP matrix) //{1 1 1}(FCC). (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The flow behaviors and microstructural evolutions during multi-stage hot deformation of a near-alpha Ti-5Al-2.5Sn alloy were studied. It was observed that the flow stress and restoration fraction in the alpha + beta phase region were lower in the non-isothermal multi-stage deformation compared to isothermal multi-stage deformation. Clear transitions were observed between different phase regions during the non-isothermal multi-stage deformation. Additionally, a dynamic phase transformation and the formation of FCC-Ti precipitations were observed during deformation.