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

Non-conventional transformation pathways have been exploited to determine the degree of refinement of the microstructure of a metastable beta-Ti alloy. This has involved a set of heat-treatments where samples, initially quenched to room temperature (RT) from above the beta transus are slowly heated to 350 degrees C, then isothermal annealed at 350 degrees C for various times prior to up-quenching to 600 degrees 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 a 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 omega precipitates playing an indirect role in the formation of the refined distribution of the alpha phase via a non-conventional transformation pathway. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.