Study On Mechanical Behavior And Deformation Mechanism Of Metastable β Titanium Alloy At Wide Strain Rate

With the increasing demand of the aerospace industry,metastable superalloys in development have attracted increasing attention due to their low elastic modulus,high strength-weight ratio and shape memory properties.For the bi-phase metastable titanium base alloys,the deformation mechanism is mainly dislocation slip,which has high yield strength,low work hardening rate and uniform elongation.As the stability of the β phase decreases,the main deformation mechanism changes from dislocation slip to mechanical twins,and eventually stress-induced martensitic transformation(SIMT),or a combination of the two.The transformation of BCC crystal phase into martensite can simultaneously improve the work hardening rate and ductility,namely,the transformation induced plastic TRIP effect,and contribute to grain refinement under severe plastic deformation,resulting in better mechanical properties.For ti-1023,a typical metastable titanium alloy,titanium alloys with different α contents have different stability,and there are few studies on their mechanical properties under high strain rates.Therefore,studying the mechanical properties of Ti1023 titanium alloy with different α contents at wide strain rates is helpful to solve the problem of high strength and high plasticity of titanium alloy at high strain rates.In this paper,the content of α phase in Ti-1023 titanium alloy was controlled by heat treatment to obtain five kinds of microstructure with different content of αphase.Then,the quasi-static compression experiment was carried out by the material experimental machine(Instron-3382)and the quasi-static tensile experiment was carried out by the material testing machine(Instron-2580).At the same time,Split Hopkinson tension bar(SHTB)was used for dynamic tensile experiments at high strain rates.SEM,electron back-scatter diffraction(EBSD)and Transmission electron Microscope(TEM)were used to characterize the microstructure of titanium alloy after deformation.At the same time,synchrotron radiation technology was used to study the phase transition behavior of titanium alloy in situ.It is found that with the increase of solution temperature from 650℃ to 770℃,α phase volume fraction,β phase stability and Moeq decrease.After solution treatment at 820℃,the microstructure consisted of a single β phase.In the compression test,the triggering stress and yield strength of βsolution treatment Ti-10V-2Fe-3Al are significantly positively correlated with the strain rate,while the increase of work hardening rate is significantly negatively correlated with the strain rate.The multistage work hardening behavior of ti-1023 alloy in single β phase or double(α+β)phase during quasi-static tensile is caused by stress-induced martensitic transformation and multiple twins in β phase and α"martensite,including {332}<113>βtwins,{111}α" {112}α"and {130}<310>α"twins.When there is single β phase or double(α+β)phase containing 0-25.9% α phase in Ti-1023 alloy,the stress induced martensitic transformation and the double-yield is obvious.When the volume fraction of α phase increases to 43.8%,the double-yield phenomenon disappears.In the process of tensile deformation and compression deformation,SIMT shows asymmetry.Compared with tensile deformation,compression deformation has lower trigger stress.In addition,at high strain rates,the coordination deformation of α "martensite,α phase and βphase in ti-1023 duplex alloy leads to the formation of {111}α" internal twin,kking,netted and banded α "martensite,which makes it have a high work hardening ability.With the increase of α phase fraction and strain rate,the dynamic yield strength and ultimate tensile strength increase,while the uniform elongation and the product of uniform elongation and ultimate tensile strength show opposite trends at high strain rate.