Isothermal kinetics of β ↔ α transformation in Ti-55531 alloy influenced by phase composition and microstructure. (15th September 2017)

• Record Type: Journal Article
• Authors: Chen, Fuwen; Xu, Guanglong; Zhang, Xiaoyong; Zhou, Kechao
• Is Part Of: Materials & design. Volume 130(2017)
• Page Start: 302
• Page End: 316
• Publication Date: 2017-09-15
• Subjects: Ti-55531 -- Phase transformation -- Microstructure -- Isothermal kinetics -- TTT diagram -- JMA theory; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2017.05.078
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: 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: Highlights: The TTT diagrams of Ti55531 with different preset microstructure show different phase transformation behaviors. The 'β-quenched' alloy has highest nose temperature and shortest incubation time in secondary α precipitation. The sequence of overall transformation rate of α precipitation varies with temperature. The αlamellar → β shows lower starting temperature, shorter incubation time, and faster overall rate than αequiaxed → β.