| Usually,5–10%of overall deformation work is absorbed by a plastically deformed metal or alloy material and absorbed work mainly associates with formation of a dislocation structure during deformation.So the different deformation mechanisms of plastic deformation can lead to the accumulation of various amounts of energy via the occurrence of slip-slip and dislocation-twin interactions.The amount of deformation stored energy has a significant influence on the nucleation and growth of new grains during recrystallization,which can further affect microstructure evolution and grain texture.Serveral studies pointed out that the deformation mode of zirconium and the contribution of slip and twinning depend on crystallographic texture,so that the magnitude of stored energy is orientation-dependent.In addition,the desirable specific properties of zirconium alloys are usually determined by the microstructure evolution during hot deformation,which is closely related to the dynamic recrystallization?DRX?process.Therefore,systematical investigation on the microstructure evolution and the DRX mechanism for the new designed alloy under different deformation conditions is quite essential.In this work,a Zr-1Sn-0.3Nb alloy plate with a typical bimodal basal texture and two Zr 702 plates with a fiber basal texture and different grain sizes were used.Compression experiments were performed by using a Gleeble-3500 thermal simulator.Electron back-scattered diffraction?EBSD?,transmission Kikuchi transmission diffraction?TKD?and electron microscopy?TEM?techniques were used to characterize microstructure and texture evolution during deformation.Moreover,slip systems activity calculated by visco-plastic self-consistent?VPSC?model was performed.The effects of the slip systems and twins on the DRX mechanisms,microstructure and texture of zirconium alloys deformed at different temperatures,strain rates and strains were discussed.The main conclusions are summarized below:?1?At the early deformation stage of Zr-1Sn-0.3Nb alloy deformed at 700 oC and at two strain rates,0.001 s-1 and 1 s-1,VPSC modeling indicated that basal slip,prismatic slip,pyramidal<a>slip and pyramidal<c+a>slip simultaneously accommodated the plastic deformation in the 0o sample,but that the primary operation slip in the 90o sample were prismatic slip,pyramidal<a>slip and basal slip.At 1 s-1 and10 s-1,the DRX process was mainly governed by nucleation,which was caused by the combined effects of high stored energy and short deformation time for grain boundary migration,and the onset of DDRX was enhanced by the operation of all four slip modes,especially pyramidal<c+a>slip.At 10 s-1,a high dislocation density in the vicinity of the{101?1}twins and the distortion and subdivision of the{101?1}twins provided more sites for DRX nucleation,thus,the{101?1}twins accelerated the DRX process.At 0.001 s-1,the DRX process was governed by both bulging of original grain boundaries and subgrain growth,in this case,the DRX process was less affected by the activity of pyramidal<c+a>slip,and the grain rotation at the first deformation stage promoted the DRX process.?2?During the deformation of Zr-1Sn-0.3Nb at 700 oC and at three strain rates,0.001 s-1,1 s-1 and 10 s-1,the development of the recrystallized grain's orientation was dominated by the macroscopic plastic strain imposed,in other words,the rotations of the recrystallized grains followed these of the parent grains.Finally,the textures of the two samples were mainly controlled by the operation of the slip modes but not the DRX process.In the 0o sample,the texture was steady,and the activity of all four slip modes did not significantly change the texture.In the 90o sample,the activity of basal slip generated a<c>axis rotation toward the compression direction,and the operation of prismatic slip oriented a{101?0}prismatic plane toward the plate rolling direction?RD?.Finally,a bimadol basal texture and a{101?0}//RD texture component formed in the 90o sample.?3?During the deformation of Zr-1Sn-0.3Nb at 300-650 oC and at a strain rate of0.001 s-1,the DRX mechanisms changed with increasing deformation temperature.At300 oC,the DRX process was associated with the activity of pyramidal<c+a>slip,since cross-slip and climb took place more readily than for other slip systems,and thus the formation of high angle boundaries was easier.At 400-550 oC,increasing the deformation temperature enhanced the grain boundary mobility,the DRX mechanisms transformed from dynamic recovery?DRV?to bulging of original grain boundary.At550-650 oC,the DRX process was governed by both bulging of original grain boundary and subgrain growth,and the critical dislocation density for the occurrence of DRX decreased with increasing deformation temperature.At 500-650 oC,the operation of all four slip modes?especially pyramidal<c+a>slip?promoted the DRX process.?4?In order to reduce the impact of the second phases on the grain boundary mobility,two Zr 702 plates with different initial grain sizes were used.During the deformation of Zr 702 at 700 oC and at a strain rate of 0.001 s-1,the DRX process was governed by both bulging of original grain boundary and subgrain growth,and the DRX process was less affected by the initial grain sizes,indicating that the subgrain growth was the main operating DRX mechanism.And the subgrain growth mechanism was less affected by the activity of pyramidal<c+a>slip and the fraction of the initial grain boundaries.With the initial grain size increasing,the critical strain for the onset of DRX decreased due to the lower fraction of grain boundary,on the other hand,the higher dislocation density at the interior of the grain promoted CDRX. |
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