Ti–10Mo–7Al合金の焼戻し誘起マルテンサイトの形成機構

The formation mechanism of αAA–martensite (αAAMt) induced by tempering at 450–550℃ for a short time was investigated using Ti–10Mo–7Al alloy. The solution treated and quenched (STQ) sample was composed of β phase and a small amount of αAAMq, and a large amount of αAAMt was generated by rapid tempering at 550℃–3 s using a salt bath. However, αAAMt was completely transformed into a single β phase by aging at 200℃ for 3 min. Reversibility was observed between the αAAMt transformation and the β reverse transformation. In–situ high–temperature X–ray diffraction measurements revealed that αAAMq → β reverse transformation occurred at 200℃ and that a thermally activated αAAiso was generated at 450℃ due to the slow heating rate. In–situ optical microscopic observation of STQ sample with rapid lamp heating revealed that αAAMt was formed during heating process. However, αAAMt did not generate under following conditions; that is, a slow heating rate, thin sample plate, and a small temperature difference until tempering by preheating. On the other hand, rapid tempering using thick plate from liquid nitrogen (−196℃) to 250℃ was performed to ensure a sufficient temperature difference, but αAAMt was not generated at all. From the cross–sectional observation of the STQ plate, it was found that αAAMq was hardly formed on the surface of the sample, but was formed abundantly inside the sample. On the other hand, in the rapidly tempered plate, a large amount of αAAMt was distributed in the surface layer than inside sample. These results suggest that the thermal compressive stress induced by rapid heat treatment contributes to the formation of α''M.

出典：竹元 嘉利, 安野 実希子, 池本 雅基, 安藤 寛幸, 清水 一郎, Ti-10Mo-7Al合金の焼戻し誘起マルテンサイトの形成機構, 日本金属学会誌, 2021, 85 巻, 11 号, p. 405-412, https://doi.org/10.2320/jinstmet.J2021027