Solid Phase Transformation Kinetics And Microstructure Evolutions Of Ti-B19 Alloy

Ti-B19 alloy is a kind of metastable β titanium alloy which has been developed by China for a certain key project independently, and it can be strengthen through heat treatment to get a good match of strength, plasticity and toughness. The microstructure evolutions of alloy are mainly depended on the phase transformation during the heat treatment processing with a certain hot deformation processing, and meanwhile, it influences the alloy mechanical properties strongly, so it is very important and valuable to study the phase transformation performance of Ti-B19 not only in theory but also in engineering applications.On the base of analyzing the factors which influence the phase transformation performance of titanium alloys, the phase transformation kinetics and mechanisms of Ti-B19 alloy during the isothermal treatment and continuous cooling conditions have been studied in the present work by the methods of in-situ electric resistivity measurements and synchrotron X-ray diffraction technology etc. systematically. The nucleation and growth mechanism of new formed phase as well as the microstructure evolutions have been investigated, and the TTT and CCT diagram of the Ti-B19 alloy have also been established. The primary coverage of this research works mainly involves the following items:The isothermal phase transformation kinetics and mechanisms of Ti-B19 alloy during isothermal treated at 300℃ to 700 ℃ have been studied systemically, and the results indicated that there is only ω phase transformation occurs at 300℃, and a mixed phase transformation process of ω and a phase can be observed during treated at 350℃. When the isothermal treatment temperature is above 400℃, there are only a phase transformation occurs. The highest isothermal transformation rate appears at range of 500℃ to 550℃, where the phase transformation driving force and the solute element diffusion rate achieves the optimum matching. The JMA kinetics equation of isothermal phase transformation in Ti-B19 alloy between 300℃ and 700℃ has been obtained base on the above research results. The values of Avrami exponent n, temperature constant K and the phase transformation activation energy E of Ti-B19 alloy have also been got based on the above analyzing. The isothermal phase transformation kinetics between 500℃ and 550℃ has been predicted depended on the calculated JMA equation and the result quiet agree with the experimental one. The TTT diagram of Ti-B19 has been established according the experimental and calculated results, and...