Synchrotron X-ray diffraction characterization of phase transformations during thermomechanical processing of a Ti38Nb alloy

• Published in: Rare metals 2021-11, Vol.40 (11), p.3269-3278
• Main Authors: Meng, Qing-Kun, Li, Huan, Zhao, Chong-Hang, Ma, Wen, Wei, Fu-Xiang, Sui, Yan-Wei, Qi, Ji-Qiu
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Beta phase; Biomaterials; Chemistry and Materials Science; Cold rolling; Dislocation density; Energy; Martensitic transformations; Materials Engineering; Materials Science; Mechanical properties; Metallic Materials; Metallurgy & Metallurgical Engineering; Modulus of elasticity; Nanoscale Science and Technology; Original Article; Phase transitions; Physical Chemistry; Room temperature; Synchrotron radiation; Synchrotrons; Temperature; Thermomechanical treatment; Titanium base alloys; X-ray diffraction
• ISSN: 1001-0521; 1867-7185
• DOI: 10.1007/s12598-021-01763-8

The phase transformations during thermomechanical processing can be employed to optimize mechanical properties of β - type Ti alloys. However, such understandings are still lacking for the alloy consisting of dual β + α″ phases in solution-treated and quenched state. In this paper, the phase transformations in a Ti38Nb model alloy subjected to different thermomechanical processing were investigated by using synchrotron X - ray diffraction (SXRD) experiments, and their influence on the Young’s modulus was discussed. The results indicated that high-density dislocations introduced by cold rolling still existed after annealing at temperatures lower than 573 K, which can decrease the martensitic transformation start temperature to below room temperature. With annealing temperatures increasing, the α″ → β, β → ω iso , and β → α phase transformations occurred successively. At annealing temperature of 473 K, the specimen consisted of a trace of α″ and ω phases as well as dominant β phase which was kept to room temperature by the high density of dislocations, rather than by the chemical stabilization. As a result, an ultralow Young’s modulus of 25.9 GPa was realized. Our investigation not only provides in - depth understandings of the phase transformations during thermomechanical processing of β - type Ti alloys, but also sheds light on designing biomedical Ti alloys with ultralow Young’s modulus. Graphic abstract 抽象 β钛合金在热机械处理过程中的相变可以用来优化其机械性能。然而对于固溶态为β + α″的双相合金, 其相变和性能关系的研究尚且缺乏。本文利用同步辐射X射线技术研究了Ti38Nb合金在不同热机械处理状态下的相组成, 并讨论了其对杨氏模量的影响规律。结果表明冷轧引入的高密度位错在低于573 K退火后仍然存在, 这可以将马氏体相变点降至室温以下。随退火温度的升高, α″ → β, β → ω iso 和β → α相变依次发生。当退火温度为473 K时, 样品中主要由β相组成并含有少量α″和ω相。这其中β相是通过高密度位错保留至室温而非化学成分稳定化。因此合金可以实现25.9 GPa的超低杨氏模量。本研究不但对β钛合金在热机械处理过程中的相变行为提供了深入理解, 而且为超低杨氏模量生物医用钛合金的开发提供了新思路.