Study On Microstructure Evolution Of Ti₃Al Based Alloy During Hot Processing

Ti₃Al based alloy is a kind of Ti-Al intermetallic compound,which has many advantages,such as low density,high specific strength,high elastic modulus,oxidation resistance and corrosion resistance at high temperature.Ti₃Al based alloys have wide potential applications in aerospace industry.However,the Ti₃Al based alloy has poor plasticity at room temperature.Its application is limited because of difficult forming and high manufacturing cost.The superplasticity of materials can be used to solve the problem effectively.At present,the research on the hot deformation behavior of Ti₃Al based alloys is not perfect.The coupling relationship of deformation condition,mechanical behavior and microstructure evolution of Ti₃Al based alloy has been studied in this paper.The solution aging heat treatment is carried out to improve the mechanical properties.In this paper,mechanical properties of Ti₃Al based alloy under different deformation conditions were investigated by high temperature tensile experiments.The flow stress and peak stress on different deformation temperature and strain rate were analyzed.The results show that the flow stress of Ti₃Al based alloy increases rapidly with the increase of strain,and then decreases gradually.The strain rate sensitivity index m is 0.384 at 980?.At 980?,2×10^-4 s^-1 the maximum of the elongation is 710.5%.In this paper,based on the true stress true strain curves obtained from high temperature tensile tests,the constitutive equation of Ti₃Al based alloy was established,and the activation energy of thermal deformation Q was 472.7992k J·mol^-1.Based on Arrhenics model and Backofen model,the constitutive equation of Ti₃Al based alloy is established,and the fitting results of Backofen model are more suitable for Ti₃Al based alloy.The numerical relationship between strain softening coefficient r,difference of strain??and ln Z is established,which quantitatively describes the degree of softening of Ti₃Al based alloy.By means of SEM,TEM and XRD,the microstructure evolution law of Ti₃Al based alloy during hot deformation has been obtained.The higher the temperature is,the less the?₂ phase is.The temperature has a promoting effect on the phase transformation process of?₂ phase to B2 phase.The higher the strain rate is,the more the?₂ phase is.The strain rate has a blocking effect on the phase transformation process of?₂ phase to B2 phase.The larger the strain is,the less the?₂ phase is.The deformation has a promoting effect on the phase transformation process of?₂ phase to B2 phase.With the increase of temperature,the equiaxed degree of Ti₃Al based alloy is increases.With the increase of stain rate,the equiaxed degree of Ti₃Al based alloy is decreases.With the increase of the strain,the equiaxed degree of Ti₃Al based alloy increases.The fracture mode of Ti₃Al based alloy at room temperature is brittle fracture,and the fracture mode at the temperature of range 940?to 1020?and strain rate of 2×10^-4s^-1is ductile fracture.In this paper,the solid solution treatment and aging treatment of Ti₃Al based alloy original sheet were studied.The influence of temperature and holding time on the mechanical properties of the alloy were investigated.The higher the solution temperature,the greater the hardness of Ti₃Al based alloy is.The longer the holding time is,the lower the hardness of Ti₃Al based alloy is.The hardness of Ti₃Al based alloy was significantly improved after aging treatment at low temperature?750??,and the hardness decreased after the aging treatment at high temperature?880??.The aging treatment was carried out on Ti₃Al based alloy after solution treatment at 950?.The yield strength decreased and the yield strength ratio became smaller.After the aging treatment at the 815?,the material strength ratio was the smallest.