Study On Control Of Basket-weave Microstructure Of TC21 Titanium Alloy And Its Quantitative Relationship With Tensile Properties At Room Temperature

TC21 titanium alloy is a kind of high strength and high toughness damage tolerance titanium alloy researched independently after TC4-DT in our country.The alloy has been widely used in the aerospace industry due to its excellent comprehensive properties.Because of its high strength and good anti-crack ability,TC21 titanium alloy with basket-weave microstructure is used on the plane as load-bearing material.Therefore,in order to provide a theoretical basis for regulating the microstructure parameters of TC21 titanium alloy,making its plasticity,strength and toughness match well.The microstructure evolution rules of TC21 titanium alloy during the high-temperature deformation was be studied in the paper.Also,the quantitative relationship between the microstructure parameters and mechanical properties was also explored..In this project,the thermal compression simulation experiment of TC21 titanium alloy was firstly carried out by Gleeble3500 thermal simulation machine,analyzed the change of rheological stress and microstructure of the alloy in different condition of temperature(890??990?),the strain rate(0.01?10s^-1)and deformation(40%,60%)and then based on the Arrhenius experience formula by using multiple linear regression method to establish the model of the constitutive equation of the alloy.Based on the results of the heat compression experiment,different forging and heat treatment schemes were designed,the original billet was subjected to quasi-forging,and the billet was treated by double annealing,the effects of different cooling methods and heat treatment processes on the microstructure of alloy nets was studied.And then studied the influence of basket-weave microstructure parameters on tensile mechanical properties,determined the main parameters affecting the tensile properties of the alloy and established their quantitative relationship with the tensile properties.The specific research contents of this paper are as follows:(1)TC21 titanium alloy has obvious rheological softening during high temperature deformation,the flow stress increases with decrease of temperature and increase of strain rate,The change of deformation degree has no significant effect on it,and discontinuous yielding occurs.Based on the Arrhenius empirical formula and the stress-strain data,the constitutive equation of TC21 titanium alloy was established by the multiple linear regression method.(2)The results show that the microstructure of TC21 titanium alloy is sensitive to temperature and strain rate during high temperature deformation was analyzing.When the deformation temperature of(?+?)two-phase region increases,the microstructure gradually coarsens.When the temperature is close to the phase transformation point,the phase transformation of?-?occurs and the dynamic recrystallization of?-grains occurs.The dynamic recrystallization and dynamic recovery of microstructure were carried out simultaneously during the deformation of single phase zone.With the increase of temperature and strain rate,the degree of dynamic recrystallization is enhanced,and the effect of dynamic recovery is also increased.(3)Analysis of TC21 titanium alloy quasi-beta?forging micro-tissue found that the forging cooling method has a greater impact on the shape of the post-forging tissue.When the water is cold after forging,the cooling speed is too fast,and only?grains are observed after the alloy forging micro-tissue,and no change???phase tissue is observed.When the air is cold after forging,the cooling speed is slow,and the needle-shaped alpha phase is extracted from the crystal boundary to the crystal in the alloy microstructure.Double heat treatment of the forged alloy specimen found that the first heavy annealing temperature had a great influence on the length,width and content of the lamellar?phase of the basket tissue,and the second heavy annealing temperature mainly affected the secondary?phase size.After deformation,the sample is optimal lysing in the shape of the net basket when the double annealing is at900?,1h/AC and 590?,4h/AC conditions.(4)The effect of the basket-weave microstructure on the mechanical properties of TC21 alloy was studied.The results show that the strength and plasticity of TC21titanium alloy decrease with the increase of?phase content and thickness.The effect of aspect ratio of the lamellar?phase is opposite,with the increase of aspect ratio,the strength of alloy increases and the plasticity decreases.Based on the analysis of the influence of the structure parameters on the mechanical properties,the quantitative relationship between the main characteristic parameters(lamellar?phase content,thickness,aspect ratio)and the tensile properties of titanium alloy basket-weave microstructure was established by using the quadratic polynomial functions.