Exploring the Phase Transformation in β-Quenched Ti-55531 Alloy During Continuous Heating via Dilatometric Measurement, Microstructure Characterization, and Diffusion Analysis

Abstract

Phase transformations of the β-quenched Ti-55531 alloy during continuous heating were studied by combining dilatometric measurement with phase analysis, microstructure observation, and local composition mapping. The corresponding transformation sequence can be verified as β → ω, β + ω → β + α, β → α, and α → β. By revisiting the individual phase transformations in the aforementioned transformation sequence, the variations of macro volume discovered in dilatometer test were reinterpreted based on three mechanisms, i.e., modification of crystallographic symmetry, thermodynamically partitioning, and diffusion kinetics. The interplay of different mechanisms was discussed for individual transformations, especially for the combinative partitioning and diffusion kinetic mechanisms of governed α ↔ β transformation. The pileups of Al atoms behind the growing α/β interface during β → α and of Mo atoms in the β side of α/β interface during α → β were observed and explained by incorporating the diffusion kinetic mechanism. All of these discoveries and discussions provided a deeper understanding of the phase transformations in Ti-55531 alloy.