Mechanism In Plastic Deformation And Microstructure Evolution Of An ?/? Titanium Alloy TC21

The excellent combination of mechanical and physical properties make titanium and its alloys as an indispensable key structural metals in aerospace industries.However,their plastic deformation mechanisms and microstructures evolution are really complicated,which are still lack of systematic researches.In this paper,we took high-strength TC21 titanium alloy as a raw material to systematically study microstructure evolution and mechanism,accommodation mechanism during plastic deformation process in room and thermal temperatures and annealing recrystallization behavior in dual-phase area by combination of experimental characterization methods including metallographic microscope(OM),scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD),transmission electron microscopy(TEM),et al.The main conclusions are summarized below:(1)The slip activation and strain accommodation mechanism of ? and ? phases were studied by plastic deformation experiment at room temperature.Basal,prismatic and pyramidal <a> slip are mainly observed in ? phase,and the first two are the dominant deformation modes.The lamellar and equiaxed microstructures are mainly governed by basal and prism slip modes,respectively.The main slip modes observed in ? phase are {110} and {112}.The slip activation and transfer phenomenon are perfectly explained by Schmid criterion and strain accommodation factor(m'),respectively.The Burgers orientation relationship have a remarkable effect on the plastic deformation.(2)The evolution laws and accommodation mechanisms of three kinds of microstructures(primary equiaxed ?,secondary lamellar ? and ? matrix)of TC21 titanium alloy were studied by thermal deformation at dual-phase area(820-940 ?).Increasing the deformation temperature and reducing the strain rate can induce the flow stress curve to quickly reach a steady state.Increasing the strain rate and deformation temperature can promote dynamic recrystallization(DRX)and DRX grains' growth.When the deformation temperature reaches 900 ?,? phase grains grow up obviously,and the content of secondary ? phase decreases,and the morphology of granular and acicular ? phase appears.? phase is more prone to DRX than ? phase,and ? and ? phase occur the mutual accommodation during dynamic deformation.The main recrystallisation texture component of ? phase is {001}<100> cube texture.(3)The static recrystallization behavior(SRX)of hot-rolled TC21 alloys were investigated by annealing process.After rolling deformation,the initial lamellar structures formed kink bands,bending,broken and spheroidization phenomenon and primary equiaxed ? phases were mainly elongated.With the increasing of annealing temperature and time,SRX phenomena of rolled microstructures gradually became more and more significant,and microstructures gradually equiaxed.The optimum spheroidizing temperature is about 880 ?.It was found that a rare debris microstructure was formed by the growth and annexation process at 940 ?.In ? phase of the equiaxed structures,a comparably strong hot rolling texture is created,while ? phase contains {001}<110> and {111}<112> fiber texture.