The indirect influence of the ω phase on the degree of refinement of distributions of the α phase in metastable β-Titanium alloys

• Published in: Acta materialia 2016-01, Vol.103, p.165-173
• Main Authors: Zheng, Yufeng, Williams, Robert E.A., Sosa, John M., Alam, Talukder, Wang, Yunzhi, Banerjee, Rajarshi, Fraser, Hamish L.
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Heat treatment; Heterogeneous nucleation; Microstructure; Pathways; Phase transformations; Precipitates; Quenching; Titanium alloys; Transformations
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2015.09.053

Non-conventional transformation pathways have been exploited to determine the degree of refinement of the microstructure of a metastable β-Ti alloy. This has involved a set of heat-treatments where samples, initially quenched to room temperature (RT) from above the β transus are slowly heated to 350 °C, then isothermal annealed at 350 °C for various times prior to up-quenching to 600 °C and again isothermally annealed at that temperature, followed by quenching to RT. Interrupted treatments have also been performed so that the factors influencing the development of the final microstructure could be determined. Microstructures have been characterized by scanning and transmission electron microscopy, and atom probe tomography. It has been found that a distribution of the α phase may be formed whose scale is intermediate between the “super-refined” and “refined” versions observed in previous research. The results are consistent with precursory isothermal ω precipitates playing an indirect role in the formation of the refined distribution of the α phase via a non-conventional transformation pathway. [Display omitted]