High-temperature deformation behavior and microstructural evolution of as-cast and hot rolled-21S alloy during hot deformation

Abstract

In this study, the hot deformation behavior of an as-cast and hot rolled 21S alloy(Ti-15Mo-3Al-3Nb-0.2Si) was investigated. Based on the hot compression tests, which wereconducted at high temperatures (800-1200?C) using different strain rates (10-2-10 s-1), aprocessing map and energy efficiency value were obtained for the alloy. Furthermore, thedeformation activation energy of the alloy was calculated and the tensile properties of thealloy after the thermal treatment were analyzed. The processing map results revealed thatplastic instability occurred at a temperature of 900?C and a strain rate of 10 s-1. Over theentire temperature range the hot deformation mechanisms indicated an activation energy of269 kJ/mol and the ln Z values, calculated by the Zener-Holloman parameter, varied between17 and 32 s-1, in which the stable flow was associated with dynamic recovery and dynamicrecrystallization. Likewise, this study revealed that dynamic recovery is the dominant defor-mation mechanism in the-21S alloy at temperatures lower than 1000?C, while dynamicrecrystallization is prevalent at higher temperatures. Finally, the tensile properties of the-21S alloy depend significantly on the post-processing heat treatment. The rapid grain-growth phenomenon observed at 1200?C suggests that the practical alloy rolling conditionsmay differ from that used for hot compression tests performed in the laboratory. Theseresults demonstrate that the process optimization is significantly dependent on samplesize which affects soaking time. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under theCC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).