| Metastable type?TB8 titanium alloy has been widely used in aerospace fasteners and structural parts due to its excellent high temperature strength,creep resistance,excellent formability,good hardenability,high oxidation resistance and good corrosion resistance.The mechanical properties of the alloy structure depend on the microstructure and texture formed during the hot working process,and are affected by the initial microstructure(initial?grain size,initial?-phase morphology)and hot working parameters.In order to obtain aeronautical structural parts of TB8titanium alloy with excellent mechanical properties,it is necessary to further study the effects of different initial microstructure and hot working parameters on hot deformation behavior and microstructure and texture evolution of TB8 titanium alloy,and elaborate the effects of different initial microstructure and hot working parameters on dynamic recrystallization nucleation mechanism of TB8 titanium alloy.Taking TB8 titanium alloy as the research object,the influence of initial microstructure on the hot deformation behavior of TB8 titanium alloy and the evolution law of microstructure and texture during the hot deformation process were systematically studied.The main conclusions are as follows:(1)The initial?grain size has a significant effect on the hot deformation behavior of TB8 titanium alloy.The fine?grains can reduce the flow stress and thermal deformation activation energy of the alloy,and promote the dynamic recrystallization of the alloy.Based on the analysis of thermal processing diagrams,this paper determines that the optimized thermal processing parameters for fine-grained alloys are 900?/10-3s-1,and the optimized thermal processing parameters for coarse-grained alloys are 10-3s-1,indicating that the fine-grained alloys can also reduce the hot working temperature of the alloy.(2)Based on DEFORM-3D finite element simulation,the d DRXand XDRXdynamic models of DRX have been established in this paper.The d DRXand XDRXincrease with the increase of deformation temperature and decrease of strain rate.During the thermal deformation process,the effective strain inside the sample and the distribution of the recrystallized grain volume fraction are not uniform,and the maximum value is distributed in the center of the cross section of the deformed sample along the compression axis.(3)Based on EBSD microstructure analysis,the dynamic recrystallization mechanism of TB8 titanium alloy during hot deformation mainly includes continuous dynamic recrystallization mechanism(CDRX)and discontinuous dynamic recrystallization mechanism(DDRX).In the process of hot deformation,strain has a significant effect on the texture evolution of TB8 titanium alloy.At 0.2 true strain,the deformed sample mainly contains?-fiber texture,?-fiber texture and?-fiber texture.As the true strain increases from 0.2 to 0.8,the volume fraction of{111}<110>,{112}<110>and{111}<112>textures decreases significantly,while the volume fraction of{001}<100>textures The score increased significantly.{011}<100>The volume fraction of the texture increases with the true strain from 0.2 to 0.8,first increases and then decreases.When the true strain is 0.8,the main texture is divided into{001}<100>and{011}<100>textures.(4)When the TB8 titanium alloy with lamellar?-phase structure undergoes thermal deformation in the?+?two-phase zone,when the strain rate is 1 s-1,when the temperature is higher than 650?,the rheological curve shows a stress drop phenomenon.With the decrease of strain rate and increase of temperature,the phenomenon of stress drop disappears.When the strain rate is 0.001 s-1,the rheological curves at 750°C and 800°C show typical dynamic recrystallization characteristics.The relationship model between the values of?,A,n and Q and the true strain has been established.The value of?increases with the increase of the true strain,while the values of A,n and Q gradually decrease with the increase of the strain. |
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