Atomic-scale observation of non-classical nucleation-mediated phase transformation in a titanium alloy

• Published in: Nature materials Vol. 21; no. 3; pp. 290 - 296
• Main Authors: Fu, Xiaoqian, Wang, Xu-Dong, Zhao, Beikai, Zhang, Qinghua, Sun, Suyang, Wang, Jiang-Jing, Zhang, Wei, Gu, Lin, Zhang, Yangsheng, Zhang, Wen-Zheng, Wen, Wen, Zhang, Ze, Chen, Long-qing, Yu, Qian, Ma, En
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2022
• Subjects: 119/118; 639/301/1023/1026; 639/925/930/12; Alloys - chemistry; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Hot Temperature; Materials Science; Molybdenum - chemistry; Nanotechnology; Optical and Electronic Materials; Phase Transition; Titanium - chemistry
• ISSN: 1476-1122; 1476-4660; 1476-4660
• DOI: 10.1038/s41563-021-01144-7

Two-phase titanium-based alloys are widely used in aerospace and biomedical applications, and they are obtained through phase transformations between a low-temperature hexagonal closed-packed α-phase and a high-temperature body-centred cubic β-phase. Understanding how a new phase evolves from its parent phase is critical to controlling the transforming microstructures and thus material properties. Here, we report time-resolved experimental evidence, at sub-ångström resolution, of a non-classically nucleated metastable phase that bridges the α-phase and the β-phase, in a technologically important titanium–molybdenum alloy. We observed a nanosized and chemically ordered superstructure in the α-phase matrix; its composition, chemical order and crystal structure are all found to be different from both the parent and the product phases, but instigating a vanishingly low energy barrier for the transformation into the β-phase. This latter phase transition can proceed instantly via vibrational switching when the molybdenum concentration in the superstructure exceeds a critical value. We expect that such a non-classical phase evolution mechanism is much more common than previously believed for solid-state transformations. A full kinetic pathway of a non-classical nucleation-induced phase transformation through metastable states is elucidated at sub-ångström resolution in a technologically important titanium alloy.