Probing into the Yield Plateau Phenomenon in Commercially Pure Titanium During Tensile Tests
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Probing into the Yield Plateau Phenomenon in Commercially Pure Titanium During Tensile Tests Xiaohui Shi1 · Zuhan Cao1 · Zhiyuan Fan1 · Ruipeng Guo1 · Junwei Qiao1 Received: 29 June 2020 / Revised: 13 September 2020 / Accepted: 20 September 2020 © The Chinese Society for Metals (CSM) and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract To explain the intrinsic mechanism of the yield plateau phenomenon in commercially pure titanium, the tensile behaviors of commercially pure titanium specimens after 91.6% cryorolling and subsequent annealing at 280 °C, 335 °C, 450 °C and 600 °C have been studied. The results show that the yield plateau phenomenon is a result of dislocation behaviors controlled by grain size and thus only exists within a given range of mean grain size. α grain boundaries are the main dislocation multiplication sources of commercially pure titanium. Fine-grained microstructure could offer numerous dislocation multiplication locations during deformation. Once the applied stress is above the yielding strength, dislocations multiply rapidly and the mobile dislocation density is high. To retrieve the imposed strain rate, the mean dislocation velocity is bound to be low. Therefore, it takes time for them to interact with each other. As a result, the movement of dislocations is hardly blocked and the deformation could continue at a nearly constant applied stress. Consequently, the so-called yield plateau behavior presents in the tensile curves. The disappearance of yield plateau phenomenon in coarse-grained and ultrafine-grained microstructures is attributed to the quick realization of the mutual interactions among dislocations at the initial stage of tensile test. Keywords Yield plateau · Commercially pure titanium · Tensile test · Grain size · Dislocation
1 Introduction The yield plateau (YP) phenomenon, which is also named yield point elongation, is a special yielding behavior during mechanical tests of many kinds of metals and alloys [1–18]. It is characterized by a region of approximately constant stress in the stress–strain curve following the yield point. The mechanisms of YP for different composition systems can be totally different. YP was early found in low-carbon steel by W. Lüders. The dynamic strain aging effect caused by the interaction between dislocations and interstitial atoms (typically C, N) is deemed as the reason [2]. Inagaki et al. [3] studied the YP phenomenon in Al–Mg alloys and found that the pinning effect of Mg atoms on dislocations is the intrinsic reason. Cheng et al. [5] studied the tensile behavior of γ-TiAl-based alloys containing boron. The work Available online at http://link.springer.com/journal/40195. * Xiaohui Shi [email protected] 1
College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China
suggested that boron can act to produce solute locking of glide dislocations and cause YP phenomena. Eipert et al. [6] discussed the YP behavior of a low-alloy Ti-0.5Si alloy and thought that the crystallographic
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