Research On The Superplastic Deformation Behavior And Plastic Evaluation Mechanism Of TC4Alloy

In recent years, with the extensive using of titanium alloys, Superplastic isothermal forging technology shows great advantage and application prospect in the field of aerospace manufacturing, especially in the producting of Engine’s compressor blade and large aviation’s complex forging. Superplastic isothermal forging technology to solve the traditional titanium alloy forging technology, such as resistance to deformation, easy to crack and higher equipment tonnage required etc. But, the different grades of titanium alloy in superplastic performance there is a huge difference, this greatly limits the redundancy of mould and forging design, is not conducive to the play of Superplasticity of titanium alloys’s the great advantage in increasing the material utilization rate and precision forming. So the study on titanium alloy’s plastic evaluation mechanism has practical significance for guiding its application in engineering.Firstly, this paper take the TC4titanium alloy as the example, High temperature compression tensile test has been did by using the Gleeble-3500thermal simulation machine andCMT4104electronic tensile testing machine. Research on the superplastic flow characteristics of TC4titanium alloy in tension and compression, and established the superplastic constitutive equation of TC4.The results show that, TC4alloy during plastic deformation at high temperature, the flow stress with strain rate’s increasing, but decrease with the rise of temperature. At the temperature>850℃and strain rate<10-2S-1, the rheological behavior show an characteristics of superplastic deformation, Seek the superplastic constitutive model conform to the following function: ε=3.79×1012[sinh(0.011914σ)]4.83exp[-313.124×103/(RT)]Secondly, analyses and determines the titanium alloy’s breakage mechanism of drum area during superplastic upsetting extrusion condition. Through the experiment measures threshold C of toughness damage and critical hole expansion ratio VGC. then, determine the superplastic upsetting test’s maximum reduction and obtain the upsetting extrusion rate’s function.The following conclusions are reached:(1) TC4alloys’s fracture mechanism is mixed mode fracture at room temperature, ductile fracture at Superplastic State. Using the hole expansion ratio theory and Cockcroft&Latham criterion,(2) During superplastic deformation, TC4alloy’s hole expansion ratio VGC0.88, Under tensile stress damage threshold C=3.15, under multiaxial stress state C=0.932. The maximum reduction is95%, And the corresponding maximum elongation rate σ=700%. superplastic isothermal forging’s plasticity index of TC4aolly:upsetting extrusion rate λ and device parameter(d,D,H,h) conform to the following function: λ=Kh/Hn2.02...