Nanocrystalline(NC)metals and alloys are prone to mechanical and thermal instability under force and thermal fields due to their high Gibbs free energy,which limits their industrial applications.In this work,by employ...Nanocrystalline(NC)metals and alloys are prone to mechanical and thermal instability under force and thermal fields due to their high Gibbs free energy,which limits their industrial applications.In this work,by employing rotary swaging(RS),bulk NC Cu–15 at.%Al alloys with both high strength and high thermal stability were prepared.Quasi-static tensile test results show that the yield strength is 1016 MPa.Moreover,the grain growth temperature was retarded up to 0.4 Tm,higher than the literature values.Microstructural characterizations revealed that after RS deformation,coarse-grained Cu–Al was refined into fibrous NC grains with a diameter of 45 nm and a length of 190 nm,and the contents of high-angle grain boundaries(GBs),low-angle GBs,and twin boundaries are 17%,45%,and 38%,respectively.Moreover,there is a significant multiscale chemical fluctuation within the grains,at the GBs,and between the grains through extreme defect accumulation.The atomistic simulation suggests that the segregation behavior of Al solute is essentially driven by the atomic size and local stress state.Besides,Al segregation greatly reduces the grain boundary energy,which further improves the thermal stability of the material.The main strengthening mechanism is Hall–Petch strengthening and the strengthening brought by the chemical fluctuations.Our work provides ideas for designing strong and thermally stable bulk NC alloys.展开更多
The excellent dislocation storage ability of bulk multi-principal element alloys(MPEAs)has been widely reported.To date,however,the underlying mechanisms of dislocation escape behavior in small-size facecentered cubic...The excellent dislocation storage ability of bulk multi-principal element alloys(MPEAs)has been widely reported.To date,however,the underlying mechanisms of dislocation escape behavior in small-size facecentered cubic(FCC)MPEAs have rarely been studied.Here,we quantitatively control the initial dislocation densities(-10^(15) m^(-2) and -10^(16) m^(-2))by large-scale molecular dynamics(MD)simulations and perform uniaxial compression simulations to compare the dislocation starvation behavior of CrCoNi with pure Cu single crystal pillars(SCPs).The analysis reveals that the CrCoNi SCPs with low initial dislocation density(-10^(15) m^(-2))can continuously accommodate mobile dislocations,and the critical dimension for dislocation starvation is about 30 nm.In particular,the CrCoNi SCPs with chemical short-range ordering(SRO)exhibit better dislocation storage and multiplication abilities than the random solid solution(RSS)samples even when the initial dislocation density is low.However,the presence of a large number of pre-existing dislocation locks governs the strong dislocation multiplication ability of the small-size RSS CrCoNi SCPs,in obvious contrast to the deformation of all pure Cu SCPs which is completely dominated by intermittent mobile dislocation starvation.Most importantly,we reveal the fundamental physics for the good dislocation storage of CrCoNi SCPs at small sizes from the perspective of chemical heterogeneity.The new phenomena reported in this work provide a unique atomic-scale perspective for understanding the microscopic physical origin of the mechanical behavior of MPEAs and the discovery of extremely slow dislocation escape behavior in small-scaled pillars,providing a reliable basis for the development of the dislocation starvation model.展开更多
基金financial supports from National Key R&D Program of China(No.2021YFA1200203)National Natural Science Foundation of China(Nos.51971112,51225102,and 52171119)+3 种基金Jiangsu Province Leading Edge Technology Basic Research Major Project(No.BK20222014)Fundamental Research Funds for the Central Universities(No.2023201001)Jiangsu Funding Program for Excellent Postdoctoral Talent(No.2023ZB091)China Postdoctoral Science Foundation(No.2023M741699)。
文摘Nanocrystalline(NC)metals and alloys are prone to mechanical and thermal instability under force and thermal fields due to their high Gibbs free energy,which limits their industrial applications.In this work,by employing rotary swaging(RS),bulk NC Cu–15 at.%Al alloys with both high strength and high thermal stability were prepared.Quasi-static tensile test results show that the yield strength is 1016 MPa.Moreover,the grain growth temperature was retarded up to 0.4 Tm,higher than the literature values.Microstructural characterizations revealed that after RS deformation,coarse-grained Cu–Al was refined into fibrous NC grains with a diameter of 45 nm and a length of 190 nm,and the contents of high-angle grain boundaries(GBs),low-angle GBs,and twin boundaries are 17%,45%,and 38%,respectively.Moreover,there is a significant multiscale chemical fluctuation within the grains,at the GBs,and between the grains through extreme defect accumulation.The atomistic simulation suggests that the segregation behavior of Al solute is essentially driven by the atomic size and local stress state.Besides,Al segregation greatly reduces the grain boundary energy,which further improves the thermal stability of the material.The main strengthening mechanism is Hall–Petch strengthening and the strengthening brought by the chemical fluctuations.Our work provides ideas for designing strong and thermally stable bulk NC alloys.
基金financially supported by the Key University Science Research Project of Jiangsu Province(No.17KJA130002)the Natural Science Foundation of Jiangsu Province(No.BK20201031)+1 种基金the National Key R&D Program of China(Grant No.2021YFA1200203)the National Natural Science Foundation of China(Grant Nos.51971112 and 52071181).
文摘The excellent dislocation storage ability of bulk multi-principal element alloys(MPEAs)has been widely reported.To date,however,the underlying mechanisms of dislocation escape behavior in small-size facecentered cubic(FCC)MPEAs have rarely been studied.Here,we quantitatively control the initial dislocation densities(-10^(15) m^(-2) and -10^(16) m^(-2))by large-scale molecular dynamics(MD)simulations and perform uniaxial compression simulations to compare the dislocation starvation behavior of CrCoNi with pure Cu single crystal pillars(SCPs).The analysis reveals that the CrCoNi SCPs with low initial dislocation density(-10^(15) m^(-2))can continuously accommodate mobile dislocations,and the critical dimension for dislocation starvation is about 30 nm.In particular,the CrCoNi SCPs with chemical short-range ordering(SRO)exhibit better dislocation storage and multiplication abilities than the random solid solution(RSS)samples even when the initial dislocation density is low.However,the presence of a large number of pre-existing dislocation locks governs the strong dislocation multiplication ability of the small-size RSS CrCoNi SCPs,in obvious contrast to the deformation of all pure Cu SCPs which is completely dominated by intermittent mobile dislocation starvation.Most importantly,we reveal the fundamental physics for the good dislocation storage of CrCoNi SCPs at small sizes from the perspective of chemical heterogeneity.The new phenomena reported in this work provide a unique atomic-scale perspective for understanding the microscopic physical origin of the mechanical behavior of MPEAs and the discovery of extremely slow dislocation escape behavior in small-scaled pillars,providing a reliable basis for the development of the dislocation starvation model.
