The Effect Of Stress On The Phase Transformation And Microstructure Of Ti-1300 Alloy

Stress aging heat treatment is a new processing of combination elastic stress field with the traditional heat treatment. The study showed that elastic stress has a great influence on phase transformation behavior and microstructure of the alloy. However, research in this area, mainly concentrated on the steel and aluminum alloy, and the influence of stress on phase transformation of titanium alloy few had been studied. Therefore, the influence of stress on phase transformation and microstructure of the Ti-1300 alloy have been studied in this paper by the high-resolution B?hr DIL-805A/D phase change instrument,combined with OM, SEM, TEM etc systematically. The main work and conclusions are as follow:The ? phase transformation of Ti-1300 alloy under 20 MPa compressive stress during continuous heating was investigated by thermal expansion method. It is found that the ? phase transformation of Ti-1300 alloy could be inhibited by 20 MPa compressive stress during continuous heating. The local activation energy of ? phase transformation for Ti-1300 alloy was determined on the basis of Kissinger–Akahira–Sunose(KAS) method. The average activation energy of ? phase transformation is about 73 KJ/mol under 20 MPa compressive stress, which is higher comparing with no stress condition(55KJ/mol). However, the activation energy decresed with increase of transformed volume fraction f?.The influence of the compressive stress on microstructure of the solid solution Ti-1300 alloy during continuous heating have been studied, The results showed that: at continuous heating rate of 3?/min, with the increase of stress,in ? phase matrix precipitated ? phase decreased and morphology of ? phase did not change significantly; precipitated ? phase gradually changed from the particles into the short needle, and orientation effect of the needle-like ? phase has become increasingly clear.The influence of compressive stress on the precipitation behavior of ? phase in the solid solution Ti-1300 alloy at 700? and 600? has been studied, The results showed: With the increase of stress, orientation effect of the needle-like ? phase has become incearingly clear; and it can be seen that the external stress has a stronger effect on the early state of ageing independent of ageing temperature.The influence of compressive stress on microstucture of the solid solution Ti-1300 alloy during double aging process was investigated, the results showed that: in double stress-aged specimens, compared with the double stress-free-aged specimens,the needle-like ? phase appeared orientation effect and the aspect ratio of needle-like ?-phase significantly increased; compared with specimens stress-aged under higher temperature after stress-free-aged under lower temperature, Ti-1300 alloy owned more fine and average microstructure by stress-free-aged treatment under higher temperature after stress-aged treatment under lower temperature.