Dynamic spheroidization kinetics behavior of Ti-6.5Al-2Zr-1Mo-1V alloy with lamellar microstructure
(1. Aeronautical Science and Technology Key Laboratory of Aeronautical Materials Hot Processing Technology,
Nanchang Hangkong University, Nanchang 330063, China;
2. Institute of Aeronautic and Manufacturing Engineering, Nanchang Hangkong University, Nanchang 330063, China;
3. Institute of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China)
Nanchang Hangkong University, Nanchang 330063, China;
2. Institute of Aeronautic and Manufacturing Engineering, Nanchang Hangkong University, Nanchang 330063, China;
3. Institute of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China)
Abstract: The dynamic spheroidization kinetics behavior of Ti-6.5Al-2Zr-1Mo-1V alloy with a lamellar initial microstructure was studied by isothermal hot compression tests in the temperature range of 750-950 °C and strain rates of 0.001-10 s-1. The results show that the spheroidized fraction of alpha lamellae increases with the increase of temperature and the decrease of strain rate. The spheroidization kinetics curves predicted by JMAK equation agree well with experimental ones. The corresponding SEM and TEM observations indicate that the dynamic spheroidization process can be divided into two stages. The primary stage is boundary splitting formed by two competing mechanisms which are dynamic recrystallization and mechanical twin. In the second stage, the penetration of beta phase into the alpha/alpha grain boundaries is dominant, which is controlled in nature by diffusion of the chemical elements such as Al, Mo and V.
Key words: titanium alloy; lamellar microstructure; spheroidization; kinetics equation