Nucleation and growth of α phase in a metastable β-Titanium Ti-5Al-5Mo-5V-3Cr alloy: Influence from the nano-scale, ordered-orthorhombic O" phase and α compositional evolution

• Published in: Scripta materialia Vol. 194; no. 15
• Main Authors: Antonov, Stoichko, Shi, Rongpei, Li, Dian, Kloenne, Zachary, Zheng, Yufeng, Fraser, Hamish L., Raabe, Dierk, Gault, Baptiste
• Format: Journal Article
• Language: English
• Published: United States Elsevier 19.12.2020
• Subjects: a precipitation; B-Ti; diffusional-displacive transformation; MATERIALS SCIENCE; nucleation and growth; phase transformations
• ISSN: 1359-6462; 1872-8456

We investigated the nucleation and growth of α precipitates in the presence of nano-scale, titanium-rich, ordered-orthorhombic O" precipitates formed during heating at 5 °C/min to 400 °C in a metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr. The O" precipitates are found to assist α nucleation by serving as preferential nucleation sites. In the very initial stages of its precipitation, the α phase is found to have formed via a coupled diffusional-displacive mode as titanium-rich plates. At this stage, aluminum partitions equally between the β matrix and the growing α precipitates, but slowly diffuses up-hill into the α phase during isothermal aging at 400 °C for 15 h. The interplay between such pre-formed metastable phases and α can be exploited to tailor the microstructure, by refining the α distribution, and consequently improve the mechanical properties of β-Ti alloys. Finally, our work paves the way for exploiting this cascade of metastable phases for further microstructural engineering of β-Ti alloys.