Study On Hot Deformation Behavior Of Forged Ti-6Al-7Nb Alloy

Ti-6Al-7Nb titanium alloy is a new type of titanium alloy engineering material after Ti-6Al-4V titanium alloy material.The titanium alloy has excellent comprehensive mechanical properties.It is one of the hot spots in the field of titanium alloy at home and abroad.It can be widely used in aerospace,aviation,military equipment,civil equipment and bioengineering equipment key components.The thermoplastic molding process of metal materials is an important link in the preparation of Ti-6Al-7Nb titanium alloy components,which determines the comprehensive mechanical properties,equipment reliability and service life of the key components of Ti-6Al-7Nb titanium alloy.To obtain a Ti-6Al-7Nb titanium alloy plastic forming member with excellent comprehensive properties,it is necessary to analyze and study the deformation ability of the material,combined with the basic material test and process simulation technology.The thermoplastic forming process of Ti-6Al-7Nb titanium alloy is studied from macro and micro angles to provide technical support for obtaining high quality titanium alloy components.On the basis of isothermal compression test,the four constitutive equations of Ti-6Al-7Nb alloy are studied by combining experimental research,theoretical calculation and finite element numerical simulation,and the accuracy and applicability of different constitutive relations and hot working diagrams are compared and evaluated to reveal the macroscopic and microscopic changes of hot-pressing deformation of Ti-6Al-7Nb alloy.The microstructure evolution of Ti-6Al-7Nb alloy under different deformation conditions is studied,the rheological and deformation strengthening characteristics of the titanium alloy are analyzed,and the dynamic recrystallization behavior of the titanium alloy is studied.The critical information of dynamic recrystallization of Ti-6Al-7Nb alloy is obtained.Moreover,the plastic forming simulation Ti-6Al-7Nb typical alloy disc parts is carried out with finite element simulation,and the influence of deformation process parameters on is analyzed.Finally,the isothermal forging process parameters of Ti-6Al-7Nb alloy disc parts with stable,high efficiency and high-quality filling are obtained.The main results are as follows:Based on the flow stress-strain data of Ti-6Al-7Nb titanium alloys,A constitutive equation model for thermal deformation of Arrhenius?Zerilli-Armstrong?Johnson-Cook and artificial neural networks was established,It is found that there are significant differences in the prediction ability of the four constitutive equation models,Hereby,The prediction accuracy of constitutive model is quantitatively evaluated by introducing correlation coefficient R and relative error absolute average ARRE.BP artificial neural network model has excellent accuracy in prediction accuracy and linear correlation.Different constitutive models are applicable to the prediction of rheological stress of Ti-6Al-7Nb titanium alloys,Arrhenius constitutive equation model is suitable for high strain rate,low temperature and high temperature deformation conditions;Zerilli-Armstrong constitutive equation model is suitable for high strain rate and low deformation temperature condition;Johnson-Cook constitutive equation model is suitable for high strain rate or lower and higher deformation temperature conditions.Through the establishment of Ti-6Al-7Nb Murty and Prasad energy dissipation diagram of thermoplastic deformation of titanium alloy,And draw the instability map under different instability criteria,The hot working drawing of Prasad?Murty and Malas theory is finally determined.Through the study and analysis of different hot working charts,it is found that strain rate and deformation temperature have a significant effect on the distribution of unstable regions,And the instability region of hot working map obtained by different instability criteria is quite different.According to the comprehensive analysis,the accuracy order of the three hot working drawings is:Murty>Malas>Prasad.Using strain rate sensitivity index m?temperature sensitivity index s and strain hardening index n₁,the plastic rheology and deformation strengthening of Ti-6Al-7Nb titanium alloy were quantitatively characterized.The influence of deformation temperature and strain rate on microstructure is studied,and the evolution law of microstructure and phase state of Ti-6Al-7Nb titanium alloy after thermal deformation are expounded.The critical strain of dynamic recrystallization of Ti-6Al-7Nb titanium alloy is analyzed,and the critical strain information of dynamic recrystallization of titanium alloy during thermoplastic deformation is determined.Through comparison of simulation results with test samples,it is found that finite element simulation can accurately predict the hot working process of Ti-6Al-7Nb alloys.In addition,the finite element simulation modeling of typical Ti-6Al-7Nb alloy disc parts is carried out,The influence of deformation process parameters on the stress condition,material volume and shape change ability of the titanium alloy is discussed.The stability,high efficiency and high quality filling can be realized when the ratio of height to diameter is 1.754,the temperature is 1073K,the deformation speed is 1.0 mm/s and the friction factor is 0.4.