Research On Hot Deformation Microstructure Evolution Of Titanium Alloy TB6

TB6 is one of the nearβtitanium alloys, which is especially attractive for aerospace forging because it presents the properties of high strength, good toughness and deep hardenability. At present, few investigators make their studies focus on the hot deformation behavior and microstructure evolution of titanium alloy TB6 in theβsingle phase field. In this paper, the hot deformation behavior and microstructure evolution of titanium alloy TB6 with two different kinds of original microstructures, namely as-casted and as-forged state, had been studied by hot compression tests in theβsingle phase field. Some predictive models of dynamic recrystallization (DRX) were established for titanium alloy TB6. This work is of important for theoretical and practical application to high temperature forging production of titanium alloy TB6 and enriching the dynamic recrystallization theory of high fault energy metals. The results show that:The true stress-strain curves of the as-casted and as-forged state titanium alloys TB6 mainly show two different characteristices, namely flow oscillation and flow softening. The effect of strain rate on flow stress is obvious, while the effect extent of deformation temperature on flow stress is more obvious at high strain rate than that at low strain rate.When the strain rate exceed 0.001s-1,the DRX develops incompletely for as-casted titanium alloy TB6, but the DRX develops more completely at strain rate of 0.001s-1 and deformation temperature exceed 1050℃.Although the grains of DRX are very fine, the volume fraction of DRX is small at the deformation temperature range of 800℃~950℃for as-forged titanium alloy TB6. The DRX develops more completely and the uniformity of microstructure has been improved at the deformation temperature range of 950℃~1150℃. When the temperature is over 1050℃, there are many over-grown grains formed in the alloy, the microstructure of the alloy is coarsened seriously. With the strain rate increases, the grains of DRX are refined, at the same time, the volume fraction of DRX is reduced, which would cause heterogeneity of grain size. When the strain rate is too low, the grains of the alloy would over grown up that might lead microstructure to coarsen.On the basis of hot compression tests data and quantitative measurements data of DRX, the average activation energy of as-casted and as-forged state titanium alloys TB6 were calculated respectively: Q1=217.5 kJ/mol, Q2=194.2 kJ/mol. The critical strain model of DRX was eastablished for as-casted titanium alloy TB6. The predictive models of the critical strain, volume fraction and grain size were modelled for as-forged titanium alloy TB6.According to the analysis on the effect of grain refinement and uniformity on the DRX microstructure which deformed under various conditions, the deformation temperature range of 950~1050℃and the strain rate of 0.01s-1 are preferable for hot deformation of the as-forged titanium alloy TB6; the deformation temperature range of 1050~1150℃and the strain rate is smaller than 0.001s-1 are preferable for hot deformation of the as-casted titanium alloy TB6.