In this study,the role of twin-twin interactions on the distributions of local defects(e.g.,dislocations)and stress fields in a magnesium alloy is investigated.A co-zone(1012)-(1012)tensile twin junction in a deformed...In this study,the role of twin-twin interactions on the distributions of local defects(e.g.,dislocations)and stress fields in a magnesium alloy is investigated.A co-zone(1012)-(1012)tensile twin junction in a deformed Mg-3wt.%Y alloy is analyzed using transmission electron microscopy(TEM).The results show that the morphology of the impinging(1012)twin is asymmetric,and the non-interacting boundary of the recipient(1012)twin is irregular.Detailed analysis of TEM images reveals that type-II pyramidal[1213](1212)dislocations concentrate in the vicinity of the twin-twin junction site.The same<c+a>dislocations are also observed inside the interacting twin domains along with a few <a> dislocations.The<c+a>dislocations emanating from the impinging(1012)twin boundary have edge character and are extended with faults parallel to the basal plane.In contrast,the<c+a>dislocations connected to the recipient(1012)twin are predominantly screw orientation and compact.Elasto-viscoplastic fast Fourier transform based crystal plasticity calculations are performed to rationalize the observed twin morphology and local dislocation distribution.The model calculations suggest that the local stress fields generated at the junction site where the two twins meet are responsible for the experimentally observed concentration of<c+a>dislocations.The calculated stress fields are asymmetric with respect to the junction site,explaining the observed asymmetric morphology of the impinging twin.Overall,these findings show strong effects of twin-twin interactions on the distribution of dislocations as well as the evolution of the twinned microstructure and as such,can help advance understanding of twinning in Mg alloys and their effect on mechanical behavior.展开更多
Compositionally complex solid electrolyte(Li_(0.375)Sr_(0.4375))(Ta_(0.375)Nb_(0.375)Zr_(0.125)Hf_(0.125))O_(3)(LSTNZH)samples are synthesized using different sintering temperatures,durations,and cooling conditions(fu...Compositionally complex solid electrolyte(Li_(0.375)Sr_(0.4375))(Ta_(0.375)Nb_(0.375)Zr_(0.125)Hf_(0.125))O_(3)(LSTNZH)samples are synthesized using different sintering temperatures,durations,and cooling conditions(furnace cooling(FC)vs.air quenching(AQ)).The temperature-dependent grain growth has been examined to investigate the microstructural evolution and the origin of exaggerated(abnormal)grain growth.At moderate temperatures,the grain growth of LSTNZH follows a cubic root growth model with an Arrhenius temperature dependence.With increasing temperature,bimodal microstructures develop,and the Arrhenius temperature dependence breaks down.Notably,increasing the temperature induces increased Nb segregation at general grain boundaries(GBs),in contrast to classical GB segregation models but suggesting premelting-like GB disordering,which can explain the observed abnormal grain growth(AGG).In addition,the large grains become faceted with increasing temperature,which occurs concurrently with the temperature-induced transitions in GB segregation and grain growth,thereby further supporting the occurrence of a GB phase-like(complexion)transition.The impacts on the densification,ionic conductivity,and hardness are also examined.This work provides a new insight into the fundamental understanding of the grain growth mechanisms of the emergent class of medium-and high-entropy compositionally complex ceramics(CCCs),which is essential for tailoring microstructures and material properties.展开更多
基金support from the U.S.Dept.of Energy,Office of Basic Energy Sciences Project FWP 06SCPE401support from the National Science Foundation under Grant Number 2051390the financial support from the National Science Foundation CMMI-1723539,the financial support from the National Science Foundation CMMI-1729829。
文摘In this study,the role of twin-twin interactions on the distributions of local defects(e.g.,dislocations)and stress fields in a magnesium alloy is investigated.A co-zone(1012)-(1012)tensile twin junction in a deformed Mg-3wt.%Y alloy is analyzed using transmission electron microscopy(TEM).The results show that the morphology of the impinging(1012)twin is asymmetric,and the non-interacting boundary of the recipient(1012)twin is irregular.Detailed analysis of TEM images reveals that type-II pyramidal[1213](1212)dislocations concentrate in the vicinity of the twin-twin junction site.The same<c+a>dislocations are also observed inside the interacting twin domains along with a few <a> dislocations.The<c+a>dislocations emanating from the impinging(1012)twin boundary have edge character and are extended with faults parallel to the basal plane.In contrast,the<c+a>dislocations connected to the recipient(1012)twin are predominantly screw orientation and compact.Elasto-viscoplastic fast Fourier transform based crystal plasticity calculations are performed to rationalize the observed twin morphology and local dislocation distribution.The model calculations suggest that the local stress fields generated at the junction site where the two twins meet are responsible for the experimentally observed concentration of<c+a>dislocations.The calculated stress fields are asymmetric with respect to the junction site,explaining the observed asymmetric morphology of the impinging twin.Overall,these findings show strong effects of twin-twin interactions on the distribution of dislocations as well as the evolution of the twinned microstructure and as such,can help advance understanding of twinning in Mg alloys and their effect on mechanical behavior.
基金supported by the National Science Foundation(NSF)Materials Research Science and Engineering Center(MRSEC)program through the UC Irvine Center for Complex and Active Materials(CCAM)under No.DMR2011967This work used shared facilities at the Irvine Materials Research Institute(also supported in part by the NSF DMR2011967)+3 种基金the San Diego Nanotechnology Infrastructure(SDNI)of UCSD,a member of the National Nanotechnology Coordinated Infrastructure(NSF ECCS-2025752)the NSF Center for Chemistry at the Space–Time Limit(CHE-0802913)the UC San Diego MRSEC shared instrumentation(NSF Grant DMR2011924)the UC San Diego Nanoengineering Materials Research Center(NE-MRC).
文摘Compositionally complex solid electrolyte(Li_(0.375)Sr_(0.4375))(Ta_(0.375)Nb_(0.375)Zr_(0.125)Hf_(0.125))O_(3)(LSTNZH)samples are synthesized using different sintering temperatures,durations,and cooling conditions(furnace cooling(FC)vs.air quenching(AQ)).The temperature-dependent grain growth has been examined to investigate the microstructural evolution and the origin of exaggerated(abnormal)grain growth.At moderate temperatures,the grain growth of LSTNZH follows a cubic root growth model with an Arrhenius temperature dependence.With increasing temperature,bimodal microstructures develop,and the Arrhenius temperature dependence breaks down.Notably,increasing the temperature induces increased Nb segregation at general grain boundaries(GBs),in contrast to classical GB segregation models but suggesting premelting-like GB disordering,which can explain the observed abnormal grain growth(AGG).In addition,the large grains become faceted with increasing temperature,which occurs concurrently with the temperature-induced transitions in GB segregation and grain growth,thereby further supporting the occurrence of a GB phase-like(complexion)transition.The impacts on the densification,ionic conductivity,and hardness are also examined.This work provides a new insight into the fundamental understanding of the grain growth mechanisms of the emergent class of medium-and high-entropy compositionally complex ceramics(CCCs),which is essential for tailoring microstructures and material properties.
