Isothermal kinetics of β↔α transformation in Ti-55531 alloy influenced by phase composition and microstructure

Publication date: 15 September 2017
Source:Materials & Design, Volume 130
Author(s): Fuwen Chen, Guanglong Xu, Xiaoyong Zhang, Kechao Zhou
The different β↔α phase transformation behaviors in Ti-55531 alloys with three types of preset microstructure were studied at isothermal conditions in the temperature range of 450–750°C. The dilatometry was employed to record the length change of the specimen. TTT diagrams for alloys with different microstructure were plotted based on the phase fractions of transformed α at different temperatures. With the help of Johnson–Mehl–Avrami theory, the calculated kinetic curves were in good agreement with experimental results. The β→secondary α transformation in the alloy with preset 'β-quenched' microstructure took place at higher nose temperature with a shorter incubation time in comparison with others, but exhibited lower steady transformation rate than that with preset 'β+αequiaxed' microstructure. With local composition analyses, the high nose temperature was interpreted by the difference in β stability and supersaturation. The alloy with preset 'β+αequiaxed' microstructure showed higher transformation rate than that with preset 'β+αlamellar' microstructure, which might be associated with the richness of defects.

Graphical abstract

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