Study On Mechanical Properties And Deformation Mechanism Of Duplex Ti-1023 Alloy

Near-βtitanium alloys are commonly used in industries such as aerospace and biomedicine because of their ultra-high specific strength,good toughness,and excellent biocompatibility.To accomplish the necessary comprehensive mechanical properties,different microstructures can be obtained through thermal deformation and heat treatment processes with various process parameters.The deformation mechanism of near-βtitanium alloys changes from stress-inducedβ→α’martensite transformation to stress-inducedβ→α"martensite transformation with the increase ofαphase,then twins,and finally dislocation slip,and with the increase ofα.As the phase increases,the yield strength increases gradually and the elongation decreases gradually.In this paper,aiming at the influence of the volume fraction and morphology of the primaryαphase on the mechanical behavior and deformation mechanism of the alloy,the deformation behavior of alloy solution aging and high temperature,medium temperature and low temperature isothermal compression is studied,and the microstructure evolution under different conditions is analyzed,explored the influence of the primaryαon the deformation mechanism and mechanical properties of the alloy,and built the relationship model of alloy thermal processing technology-microstructure-mechanical properties.The microstructure of the alloy is regulated by solution and aging treatment at different temperatures.The research shows that with the increase of the solution temperature,the content of the primaryαphase in the alloy gradually decreases.When the solution temperature is 550°C,theα-phase content in the alloy is 67.4%,and when the solution temperature is 630°C,theα-phase content is 56.7%,and as the solution temperature increases to 780°C,theα-phase content decreases to 12.6%.The yield strength and plasticity of the alloy tend to decline during tensile deformation at room temperature as theα-phase content decreases,from 918MPa to 780MPa,and due to the decrease ofα-phase content in the deformation process,the alloy appeared"double yield"Phenomenon,the elongation of the alloy is the highest after"double yielding".When the content ofαphase in the alloy is high,the main body of deformation isαphase,andβphase only participates in coordinated deformation.After deformation,αphase is broken andαphase twins are formed,and part ofαphase undergoes martensitic transformation.Acicularαphases precipitated in theβmatrix after aging,and the acicularαphases gradually became wider with the prolongation of aging time and the increase of aging temperature.When the aging temperature is 550°C and the aging time is 40min,the microhardness of the alloy is the highest,about 460HV;when the aging process is 650°C-20min-550°C-20min,the alloy has higher strength and good plasticity.The thermal deformation behavior of Ti-1023 alloy under different temperatures and different strain rates was studied.The analysis results showed that when deformed at high temperature（750°C）,only a small amount ofβphase recrystallized in the alloy with fullβstructure after high temperature deformation,mainlyαphase precipitation.When the strain rate is 0.01 s^-1,the volume fraction of the precipitatedαphase is about 16.9%,and the grain size is small.With the increase of the strain rate,theαvolume fraction increases to 23.2%,and theαphase also grows.When the primaryαphase exists in the alloy at the initial stage of deformation,the deformation mechanism of the alloy is obviously different,and a large number of recrystallized grains are formed at the grain boundaries of theβphase after deformation.As the strain rate decreases,the recrystallization volume fraction increases gradually,the recrystallization grains grow,and the primaryαphase gradually disappears during the deformation process.When the deformation of the alloy occurs at medium temperature（550°C）,a large amount of equiaxedαphases are precipitated,and theβgrains are significantly refined,with an average grain size of about 200nm.Equiaxedβphases and equiaxedαphases exist alternately.Under low temperature（350°C）thermal deformation conditions,the deformation mechanism of the Ti-1023 alloy is mainly dislocation slip and stress-induced martensiticα"phase transformation.The deformation mechanism gradually alters as the temperature rises during the isothermal compression of Ti-1023.It is mainly dislocation slip and stress-induced martensiticα"phase transformation.Medium-temperature isothermal compression promotes the precipitation ofα-phase and forms ultra-fine grains.High-temperature isothermal compression is mainly dynamic recovery（DRV）/dynamic recrystallization（DRX）.Different deformation temperatures lead to different deformation mechanisms,which eventually lead to the formation of different microstructures of the alloys,thereby exhibiting different mechanical properties.