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Thermal deformation mechanism of Ti-5Al-5V-5Mo-3Cr alloy with single phase metastable beta
May 20, 2016

Ti-5Al-5V-5Mo-3Cr alloy is a kind of high strength near beta titanium alloy, the alloy has good processing performance and mechanical properties, and has been used in the manufacture of large aircraft components. 

The thermal deformation mechanism of Ti-5Al-5V-5Mo-3Cr alloy was studied based on microstructure evolution and processing technology. The experimental temperatures were 600, 700, 800, 1000, 1100 and 900, respectively, and the strain rate was 0.001, 0.01, 0.1, 1, 10 s-1. 

The experimental results show that in the stress-strain curve, the low temperature region and the high strain rate region can be observed in the continuous flow softening phenomenon after the peak stress. However, with the increase of the deformation temperature or the decrease of strain rate, the stress-strain curve becomes more and more smooth. This is a typical behavior of beta titanium alloy during hot deformation. With the increase of temperature or the decrease of strain rate, the dynamic response is the main deformation. The rheological behavior of the alloy at 700 C was observed, and it was found that the rheological curves of the strain rate was 1 S-1 and 0.1 s-1, which were almost the same. Calculated from the stress-strain curves of hot deformation activation energy were 296 kJ mol-1 (600 to 800 DEG C, 0.001 to 0.1 s-1) and 188 kJ mol-1 (900-1 to 100 DEG C, 0.001 to 0.1 s-1), show above the beta transus temperature deformation and low strain rate deformation and stress is mainly to dynamic recovery as a guide. Small and other axial grains can be observed in the deformed microstructure at 700 degrees C, and it is found that there is a phase. The deformation modes of the beta phase are: high strain rate region, the dominant position of the sub grain deformation, the lower strain rate region, the dominant effect of superplastic deformation and grain boundary sliding.

 At 800 C and above all experimental conditions, the deformation of the microstructure of the organization are coarse. When the strain rate is 0.001 and 0.01 s-1, deformation organization has the thick of subgrains and with high angle grain boundaries of new fine grains, which suggests that continuous dynamic recrystallization plays a leading role in the vicinity of the original beta grain boundaries. On the other hand, the dynamic response of the original beta grain is frequently activated, with the increase of the strain rate, the leading role of dynamic recovery is more significant. According to the results of the processing graph, it is found that there are three regions with optimal power dissipation rate (from 40% to 50%). These three regions are related to grain boundary sliding, dynamic recovery and dynamic recovery. It is shown that the stable region appears in the low strain rate and high strain rate region, that is, when the strain rate is in the range of S-1 0.05~1, the rheological behavior is not stable.