Study On Hot Temperature Deformation Behavior And Processing Maps Of TNTZ Alloy

TNTZ alloy,a new type of medical ?-type titanium alloy of Ti-Nb-Zr-Ta series,having low elastic modulus,good wear resistance,biocompatibility and non-toxicity is widely used in artificial joints,bone transplantations,limb fixations and other biomedical materials of extremely important medical value.This paper takes TNTZ alloy with better biocompatibility as the study object,systematically studies its high-temperature deformation behavior and constitutive model and builds processing maps based on different criteria.The study results have guiding significance to TNTZ alloy process parameter optimization and performance improvement.The isothermal compression experiment with constant strain rate of TNTZ alloy were conducted by Gleeble-3500 hot simulater with a deformation temperature of 700?900? and a strain rate of 0.001?is-1.By analyzing the influence of different deformation conditions on the flow stress curve,it was found that with the increase of the deformation temperature and the decrease of the strain rate,the flow stress decreased significantly,indicating that the alloy is a more sensitive material of temperature and strain rate.Most of the curves show dynamic recovery softening and the softening is most obvious when the strain rate is 0.001s-1 and the deformation temperature is 700?750?.Based on Zener-Hollomon parameter modified Arrhenius constitutive model as:(?)=e27.26 sinh(0.00884?)5.974 exp(-286075.168/3.14T)and using PSO-BP network to establish different constitutive models for TNTZ alloy.The results show that the constitutive model established by the PSO-BP network is more suitable for the alloy.The correlation coefficient R and the average relative error E of the model are 0.9962 and 2.61%,and the deviation of the predicted value within 10%accounts for 98.93%,so the model have the better of accuracy.In addition,the thermal deformation activation energy of TNTZ alloy Q ? 286.075kJ/mol.Based on the Prasad,Murty and Malas criteria,the processing maps of the TNTZ alloy was constructed.Combined with the microstructure analysis and comparison,it was found that the processing map based on the Malas stability criterion was not applicable to the prediction of the TNTZ alloy and the Murty instability criterion was better than Prasad.The processing map constructed by the instability criterion predicts the stable deformation zone and the rheological instability zone more accurately.The results show that:based on the processing diagram of the Murty instability criterion,the rheological instability zone of the TNTZ alloy is:deformation temperature 700?720?,strain rate 0.2?1s-1,deformation temperature 720?800?,strain rate 0.018?1s-1,deformation temperature 800?900?,strain rate 0.158?1s-1,mainly showing local plastic flow;stable deformation zone range:deformation temperature 740?775?,strain rate 0.001?0.0562s-1;deformation temperature 890?900?,strain rate 0.001?0.0316s-1,dynamic recovery mainly occurs.Through the observation and analysis of the microstructure,the optimal processing parameters range is:deformation temperature 890?900?,strain rate 0.001?0.0316s-1.