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<p>Strain-induced <i>α</i><sup>”</sup> martensitic phase transformation (SIMT) critically affects the mechanical properties of metastable <i>β</i> titanium alloys. In this study, the effects of <i>β</i> grain size and oxygen content on SIMT in a Ti-12wt.%Mo alloy were systematically investigated. It is found that SIMT is promoted by a decrease in grain size and in oxygen content. The mechanistic origins of the anomalous grain size dependency and the acute oxygen content dependency of SIMT are discussed based on multi-scale microstructural characterization and state-of-the-art simulations. In the Ti-12wt.%Mo alloy, in-situ synchrotron X-ray diffraction analysis reveals that SIMT occurs before macroscopic yielding and only leads to elastic deformation of the surrounding <i>β</i> matrix due to the small transformation strain. Therefore, grain refinement does not raise the energy barrier for SIMT but rather provides more nucleation sites for strain-induced <i>α</i><sup>”</sup> martensite, thereby promoting SIMT in fine-grained Ti-12wt.%Mo alloy. In contrast, for the Ti-12wt.%Mo-0.3 wt.%O alloy, oxygen atoms substantially increase the energy barrier for SIMT, due to a change in the local configuration of oxygen atoms during the phase transformation. In addition, atom probe tomography reveals for the first time that oxygen atoms segregate at <i>α</i><sup>”</sup>/<i>β</i> phase boundaries, thereby further restricting the growth of <i>α</i><sup>”</sup> martensite.</p>

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Mechanistic origin of grain size and oxygen interstitial effects on strain-induced α” martensitic transformation in Ti-12Mo alloy

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年3月20日

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  • Yan Chong,
  • Tomohito Tsuru,
  • Masatoshi Mitsuhara,
  • Baoqi Guo,
  • Reza Gholizadeh,
  • Koji Inoue,
  • Andrew Godfrey,
  • Nobuhiro Tsuji

摘要

Strain-induced α” martensitic phase transformation (SIMT) critically affects the mechanical properties of metastable β titanium alloys. In this study, the effects of β grain size and oxygen content on SIMT in a Ti-12wt.%Mo alloy were systematically investigated. It is found that SIMT is promoted by a decrease in grain size and in oxygen content. The mechanistic origins of the anomalous grain size dependency and the acute oxygen content dependency of SIMT are discussed based on multi-scale microstructural characterization and state-of-the-art simulations. In the Ti-12wt.%Mo alloy, in-situ synchrotron X-ray diffraction analysis reveals that SIMT occurs before macroscopic yielding and only leads to elastic deformation of the surrounding β matrix due to the small transformation strain. Therefore, grain refinement does not raise the energy barrier for SIMT but rather provides more nucleation sites for strain-induced α” martensite, thereby promoting SIMT in fine-grained Ti-12wt.%Mo alloy. In contrast, for the Ti-12wt.%Mo-0.3 wt.%O alloy, oxygen atoms substantially increase the energy barrier for SIMT, due to a change in the local configuration of oxygen atoms during the phase transformation. In addition, atom probe tomography reveals for the first time that oxygen atoms segregate at α”/β phase boundaries, thereby further restricting the growth of α” martensite.