Nanograined(NG)materials often suffer from low thermal stability owing to the high volume fraction of grain boundaries(GBs).Herein,we investigate the possibility of utilizing local chemical ordering(LCO)for improving ...Nanograined(NG)materials often suffer from low thermal stability owing to the high volume fraction of grain boundaries(GBs).Herein,we investigate the possibility of utilizing local chemical ordering(LCO)for improving the thermal stability of NG FeCoNiCrMn highentropy alloys(HE As).NG HE As with two different grain sizes were considered.Tensile tests and creep test simulations were then performed to reveal the influence of LCO on the mechanical properties and thermal stability of NG HE As.After performing hybrid molecular dynamics and Monte Carlo simulations,Cr atoms were found to accumulate at GBs.By analyzing the atomic structure evolution during the deformation process,we found that the formation of LCO effectively stabilized the GBs and inhibited GB movement.In addition,dislocation nucleation from GBs and dislocation movement was also hindered.The inhibiting effect of LCO on GB movement and dislocation activity is more prominent than in the NG model with smaller grain sizes.The current simulation results suggest a possible strategy for enhancing the thermal stability of NG HEAs for service in a high-temperature environment.展开更多
Multi-principal element alloys(MPEAs)have attracted much attention as future nuclear materials due to their extraordinary radiation resistances.In this work,we have elucidated the development of local chemical orderin...Multi-principal element alloys(MPEAs)have attracted much attention as future nuclear materials due to their extraordinary radiation resistances.In this work,we have elucidated the development of local chemical orderings(LCOs)and their influences on radiation damage behavior in the typical CrFeNi MPEA by hybrid-molecular dynamics and Monte Carlo simulations.It was found that considerable LCOs consist-ing of the Cr-Cr and Ni-Fe short-range orders existed in the ordered configuration with optimized system energy.Through modeling the accumulation cascades up to 1000 recoils,we revealed that the size of de-fect clusters and dislocation loops is smaller in the ordered configuration than those in the random one,although the former formed more Frenkel pairs(i.e.,self-interstitials and vacancies).In addition,the dis-tribution of dislocation loops is relatively more dispersed in the ordered configuration,and the stair-rod dislocations related to irradiation swelling are also smaller,implying that the existence of LCOs is con-ducive to enhancing radiation damage tolerance.To understand the underlying mechanism,the effects of LCOs on the formation and evolution of defects and radiation resistance were discussed from the aspects of atomic bonding,migration path,and energy of defect diffusion,which provides theoretical guidance for the design of MPEAs with enhanced radiation resistance.展开更多
In this paper, we give further discussions about our new method of bond spherical har-monics with equal number of near neighborst, and study the molten salt LiCl and itsquenching process by means of molecular dynamics...In this paper, we give further discussions about our new method of bond spherical har-monics with equal number of near neighborst, and study the molten salt LiCl and itsquenching process by means of molecular dynamics simulation. The bond order parametersQ_l at different temperatures are calculated by averaging the Q_l values of the computer-generated instantaneous configurations at each time-step. By consulting the Q_l histogramsof the linear combination models with a parameter of square deviation σ we find that theQ_l Listograms from the simulation and those from the combination model with 90% localtetrahedron structure are very similar. The results indicate that the local bond orientationin the quenched LiCl system tends strongly to be tetrahedron. The local bond-orientationalorders in the quenching process can be described by the same linear combination, but thesquare deviation varies with the temperature. The square deviation decreases with thelowering of temperature and drops rapidly when the glass transition takes place. The bondangle distributions are also calculated and it is found that the angles gather about 109°(the=bond angle of tetrahedron) and the peaks of the distributions Lave a wider spread as temper-iature increases, in accordance with the results from Q_l.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.52101019,52071023,51901013,52122408)the financial support from the Fundamental Research Funds for theCentral Universities(University of Science and Technology Beijing,Nos.FRF-TP-2021-04C1,06500135)supported by USTB MatCom of Beijing Advanced Innovation Center for Materials Genome Engineering。
文摘Nanograined(NG)materials often suffer from low thermal stability owing to the high volume fraction of grain boundaries(GBs).Herein,we investigate the possibility of utilizing local chemical ordering(LCO)for improving the thermal stability of NG FeCoNiCrMn highentropy alloys(HE As).NG HE As with two different grain sizes were considered.Tensile tests and creep test simulations were then performed to reveal the influence of LCO on the mechanical properties and thermal stability of NG HE As.After performing hybrid molecular dynamics and Monte Carlo simulations,Cr atoms were found to accumulate at GBs.By analyzing the atomic structure evolution during the deformation process,we found that the formation of LCO effectively stabilized the GBs and inhibited GB movement.In addition,dislocation nucleation from GBs and dislocation movement was also hindered.The inhibiting effect of LCO on GB movement and dislocation activity is more prominent than in the NG model with smaller grain sizes.The current simulation results suggest a possible strategy for enhancing the thermal stability of NG HEAs for service in a high-temperature environment.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51671021,11790293,51871016,52071024,and 51961160729)the Funds for Creative Research Groups of China(No.51921001)+1 种基金the 111 Project(No.B07003)the Fundamental Research Funds for the Central Universities.
文摘Multi-principal element alloys(MPEAs)have attracted much attention as future nuclear materials due to their extraordinary radiation resistances.In this work,we have elucidated the development of local chemical orderings(LCOs)and their influences on radiation damage behavior in the typical CrFeNi MPEA by hybrid-molecular dynamics and Monte Carlo simulations.It was found that considerable LCOs consist-ing of the Cr-Cr and Ni-Fe short-range orders existed in the ordered configuration with optimized system energy.Through modeling the accumulation cascades up to 1000 recoils,we revealed that the size of de-fect clusters and dislocation loops is smaller in the ordered configuration than those in the random one,although the former formed more Frenkel pairs(i.e.,self-interstitials and vacancies).In addition,the dis-tribution of dislocation loops is relatively more dispersed in the ordered configuration,and the stair-rod dislocations related to irradiation swelling are also smaller,implying that the existence of LCOs is con-ducive to enhancing radiation damage tolerance.To understand the underlying mechanism,the effects of LCOs on the formation and evolution of defects and radiation resistance were discussed from the aspects of atomic bonding,migration path,and energy of defect diffusion,which provides theoretical guidance for the design of MPEAs with enhanced radiation resistance.
基金Project supported by the National Natural Science Foundation of China.
文摘In this paper, we give further discussions about our new method of bond spherical har-monics with equal number of near neighborst, and study the molten salt LiCl and itsquenching process by means of molecular dynamics simulation. The bond order parametersQ_l at different temperatures are calculated by averaging the Q_l values of the computer-generated instantaneous configurations at each time-step. By consulting the Q_l histogramsof the linear combination models with a parameter of square deviation σ we find that theQ_l Listograms from the simulation and those from the combination model with 90% localtetrahedron structure are very similar. The results indicate that the local bond orientationin the quenched LiCl system tends strongly to be tetrahedron. The local bond-orientationalorders in the quenching process can be described by the same linear combination, but thesquare deviation varies with the temperature. The square deviation decreases with thelowering of temperature and drops rapidly when the glass transition takes place. The bondangle distributions are also calculated and it is found that the angles gather about 109°(the=bond angle of tetrahedron) and the peaks of the distributions Lave a wider spread as temper-iature increases, in accordance with the results from Q_l.
