Twinning Deformation Behavior And Microstructural Evolution Of High-purity Titanium Sheet During Cold Rolling And Annealing

Thanks to high strength to density ratio,excellent corrosion resistance and biocompatibility,titanium(Ti)and its alloys have been widely used in aerospace,biomedicine,marine engineering and other fields.During rolling,pure Ti sheets are prone to twinning and the twins will markedly change microstructures and textures of materials.In this work,electron backscatter diffraction(EBSD),X-ray diffraction(XRD)and electron channel contrast(ECC)techniques are jointly employed to study microstructural and textural characteristics of a high purity Ti((HP-Ti))sheet subjected to cold rolling and annealing at various temperatures.Results show that:(1)During the 10%-30% rolling,the imposed strain was accommodated by both slip and twinning.As rolling reduction increases to 50%,slip overrode twinning and became the main deformation mechanism.(2)During the 10%-30% rolling,both {11-22}<11-2-3> compressive and {10-12}<10-1-1> tensile twins were activated.Multiple twinning was observed,i.e.,secondary {10-12} twins formed inside primary {11-22} twins.As a result of the formation of a number of twins,grains are considerably re-orientated,leading to significant textural changes.Particularly,an unusual basal texture was formed in the 30%-rolled sheet.With increasing the rolling reduction,twinning activity is gradually suppressed.(3)For 50%-rolled HP-Ti sheet,primary recrystallization was completed after annealing at 550°C for 1 h with a mode of discontinuous recrystallization.For annealing at 450°C,the primary recrystallization could not be completed even for 100 h,with residual deformation structures still visible.After annealing,the bimodal basal texture formed in the 50%-rolled sheet is slightly changed to have a ring-like shape around the normal direction of the sheet.