Study On Thermal Deformation Behavior And Superplasticity Of Ti-3.5Al-3.5V-0.6Mo-0.5Fe-0.6Cr Alloy

Superplastic forming technology possesses advantages such as low deformation resistance and high forming precision,and finds extensive application in aerospace and other fields.The SP700 titanium alloy,known for its low superplastic forming temperature,rapid forming rate,and high superplastic elongation,is an exceptional titanium alloy for superplastic forming.However,due to its 2%iron（Fe）content,the alloy is prone to segregation.Therefore,this study proposes a novel low-iron（Fe）titanium alloy with excellent low-temperature superplasticity,designated as Ti-3.5Al-3.5V-0.6Mo-0.5Fe-0.6Cr,using the strength of the SP700 titanium alloy as a benchmark.Employing the plane strain compression simulation test method,the thermal deformation behavior and microstructural evolution of the alloy are systematically investigated.Additionally,the superplastic tensile deformation behavior of thin sheets made from this alloy is explored,aiming to provide theoretical and experimental support for the development of the novel low-temperature superplastic titanium alloy.The main conclusions are as follows:During the plane strain compression process of the Ti-3.5Al-3.5V-0.6Mo-0.5Fe-0.6Cr alloy,temperature and strain rate significantly influence its rheological behavior.The flow stress exhibits both negative temperature sensitivity and positive strain rate sensitivity.The true stress-true strain curve at 800℃ to 840℃ shows typical dynamic recrystallization characteristics,while the curve at 860℃ to 880℃ exhibits typical dynamic recovery features.Single-pass plane strain compression experiments conducted under different deformation levels（30%to 75%）,temperatures（800℃ to 880℃）,and strain rates(1 s^-1 to 10 s^-1)reveal that the alloy has a uniform deformation temperature range of 860℃ to 880℃,with strain rates below 5 s^-1 and deformation levels below 50%.During the deformation process,the β phase undergoes significant dynamic recrystallization,and continuous dynamic recrystallization occurs in the a layer.Higher deformation temperatures,lower strain rates,and larger deformation levels result in higher levels of recrystallization in the αlayer of the microstructure.Dual-pass plane strain compression experiments involving isothermal compression and cooling compression at 860℃ to 880℃ demonstrate that the best recrystallization and spheroidization effects are achieved through cooling compression at 860℃.This process ensures uniformity of the microstructure and yields optimal recrystallization and spheroidization effects.However,it is advisable to avoid processing the alloy near the phase transition point,as the deformation temperature rise during the dual-pass compression at 880℃ can affect the recrystallization behavior of the microstructure.The Ti-3.5Al-3.5V-0.6Mo-0.5Fe-0.6Cr alloy thin sheets exhibit good superplasticity in the temperature range of 770℃ to 850℃ and at strain rates of 5×10^-4 s^-1 to 5×10^-3 s^-1,with superplastic elongation exceeding 820%in all cases.At a temperature of 830℃ and a strain rate of 1×10^-3 s^-1,the alloy achieves a superplastic elongation of 1260%.In the superplastic deformation process,higher temperatures result in lower strain rates and more pronounced grain growth.The phase transformation and grain growth during the deformation process can impact the superplasticity of the alloy.