Study On Deformation Behavior And Hot Treatment For TC21Alloy At High Temperature

TC21titanium alloy has excellent performance in an integrated such as highstrength and high toughness and been widely used in many fields. The aggregationand growth of microstructure has influence on performance under the hightemperature and low strain rate during high temperature deformation. But theseproblems can be solved by heat treatment, Therefore study on deformation behaviorand hot treatment for TC21alloy at high temperature has a great significance.In this study, a series of plastic deformation behaviors of TC21alloy hotcompression experiments on TC21alloy were conducted with Gleeble-3500thermalsimulator at deformation temperature870～990℃and strain rate0.001～10s-1.Expect to receive basketweave structure with much better comprehensiveperformance through the double annealing heat treatment to deformed structure. Theeffect of duplex annealing and the firstly annealing temperature and the secondlyannealing temperature on microstructure of TC21titanium alloy after hightemperature deformation was investigated, The main research content is as follows:(1) According to the curves of true stress-strain, activation energy Q werecalculated and constitutive equation of the maximum flow stress were established, it isfound that Q is greater than self-diffusion activation energy of pure and β titaniumalloy, indicating that dynamic recrystallization was the main softening mechanismwhile deforming in hot deformation compress experiments for TC21alloy. Dynamicrecrystallization kinetics motel was set up, the results calculated by the model areidentical to that of tests by comparison.(2) The microstructures of deformed specimens at different temperatures anddifferent strain rates were compared by optical microscope. Observed, the TC21alloyis very sensitive to the variations of deformation temperature and strain rate duringthe deformation, as deformation temperature varies870℃to990℃, the phenomenonof dynamic recrystallization and dynamic recovery was obviously. Deformationtemperature and strain rate have a significant effect on content and morphology ofprimary phase.(3) The effect of duplex annealing on microstructure of TC21alloy was relatedto deformation temperature. When the strain rate is constant, as the deformationtemperature is increased, the microstructure was turn into a bimodal structure with ahybrid structure. As the deformation temperature is increased to the β phase region, the microstructure was turn into basketweave.(4) The first annealing temperature greatly affects the amount and shape ofprimary phase. With the increase of temperature for first annealing, the content ofprimary phases decreases but secondary phases increase which leads to higherstrength but lower plasticity for TC21alloy. The fine and disperse secondary phasegrows up and coarsens and the strength of the alloy decreases with increase of thesecond annealing temperature.(5) Research comprehensively suggests that the first annealing temperature atT50℃could keep basketweave at maximum extent and the second annealingtemperature near590℃could get fine and compact second precipitating phase,therefore TC21titanium alloy can obtain the optimal mechanical properties.