Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(...Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.展开更多
The dynamic tensile deformation and fracture behavior of the Zr-based metallic glass/porous W phase composite were investigated at room temperature by means of the Split Hopkinson Tension Bar （SHTB）.It was found tha...The dynamic tensile deformation and fracture behavior of the Zr-based metallic glass/porous W phase composite were investigated at room temperature by means of the Split Hopkinson Tension Bar （SHTB）.It was found that the composite exhibited no appreciable macroscopic plastic deformation prior to catastrophic fracture and the fracture surface was perpendicular to the axial direction.Substantive micro cracks were observed along the interface between W grains or the interface between the metallic glass phase and the W phase.Scanning electron microscopy （SEM） observations revealed that vein-like patterns,dimple-like patterns and substantive ridge-like structures were the typical fracture morphologies on the fracture surface for the metallic glass phase and the morphology of the W phase is a mixture of intergranular and transgranular fracture.Based on those results referred above,the dynamic tensile deformation and fracture mechanism of the Zr-based metallic glass/porous W phase composite were discussed in detail.展开更多
Thermal residual stresses in W fibers/Zr-based metallic glass composites were measured by in situ high energy synchrotron X-ray diffraction(HEXRD). The W fibers for the composites were 300,500,and 700 m m in diameter,...Thermal residual stresses in W fibers/Zr-based metallic glass composites were measured by in situ high energy synchrotron X-ray diffraction(HEXRD). The W fibers for the composites were 300,500,and 700 m m in diameter,respectively. Coaxial cylinder model(CCM) and finite element model(FEM) were employed to simulate the distribution of thermal residual stress,respectively. HEXRD results showed that the selected diameters of W fiber had little influence on the value of thermal residual stresses in the present composites. Thermal residual stresses simulated by CCM and FEM were in good agreement with HEXRD measured results. In addition,FEM results exhibited that thermal residual stress concentrated on interface between the two phases and area where the two W fibers were the closest ones to each other.展开更多
Liquid phase sintering(LPS)is a proven technique for preparing large-size tungsten heavy alloys(WHAs).However,for densification,this processing requires that the matrix of WHAs keeps melting for a long time,which simu...Liquid phase sintering(LPS)is a proven technique for preparing large-size tungsten heavy alloys(WHAs).However,for densification,this processing requires that the matrix of WHAs keeps melting for a long time,which simultaneously causes W grain coarsening that degenerates the performance.This work develops a novel ultrashort-time LPS method to form bulk high-performance fine-grain WHAs based on the principle of laser additive manufacturing(LAM).During LAM,the high-entropy alloy matrix(Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2))and W powders were fed simultaneously but only the matrix was melted by laser and most W particles remained solid,and the melted matrix rapidly solidified with laser moving away,producing an ultrashort-time LPS processing in the melt pool,i.e.,laser ultrashort-time liquid phase sintering(LULPS).The extreme short dwell time in liquid(-1/10,000 of conventional LPS)can effectively suppress W grain growth,obtaining a small size of 1/3 of the size in LPS WHAs.Meanwhile,strong convection in the melt pool of LULPS enables a nearly full densification in such a short sintering time.Compared with LPS WHAs,the LULPS fine-grain WHAs present a 42%higher yield strength,as well as an enhanced susceptibility to adiabatic shear banding(ASB)that is important for strong armor-piercing capability,indicating that LULPS can be a promising pathway for forming high-performance WHAs that surpass those prepared by conventional LPS.展开更多
Hot isostatic pressing(HIP)is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion(LPBF).In the present research,in order to improve the relative densit...Hot isostatic pressing(HIP)is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion(LPBF).In the present research,in order to improve the relative density and mechanical property,HIP was employed on the LPBF-processed Al-Cr-Fe-Ni-V high-entropy alloy(HEA)with microcracks and pores.The microstructure evolution and property improvement induced by HIP were investigated.In the LPBF-processed HEA,the microcracks were caused by residual stress and element segregation,and these microcracks as well as the pores reduced significantly after HIP treatments.Remarkably,HIP temperature has a more critical effect on the microcrack closure than the holding time,thus,microcracks and pores still existed after HIP-1 treatment(1273 K,8 h),while HIP-2 treatment(1473 K,4 h)could close the microcracks significantly.The crack closure was attributed to the interfacial diffusion of the alloying element under high temperature accompanied by high pressure,and the degree of element diffusion at both interfaces of the cracks determined the bonding strength after crack closure.Higher temperatures at high pressure induced more adequate element diffusion and higher bonding strength.The above high temperature and high pressure also induced the growth of the L1_(2) phase and the precipitation of the B2 phase in HEA.Consequently,the tensile strength and elonga-tion of the LPBF-processed HEA after HIP-2 treatment were simultaneously enhanced(80.7%and 222.5%higher than that of LPBF-processed HEA,respectively).This could be attributed to the combined effect of microcrack/pore closure and precipitation strengthening.The strengthening effect of the B2 phase and L1_(2) phase accounted for 53%(dislocation by-pass mechanism)and 47%(dislocation shearing mechanism)of the total precipitation strengthening,respectively.展开更多
Recently,high-entropy alloys(HEAs)designed by the concepts of unique entropy-stabilized mechanisms,started to attract widespread interests for their hydrogen storage properties.HEAs with body-centered cubic(BCC)struct...Recently,high-entropy alloys(HEAs)designed by the concepts of unique entropy-stabilized mechanisms,started to attract widespread interests for their hydrogen storage properties.HEAs with body-centered cubic(BCC)structures present a high potential for hydrogen storage due to the high hydrogen-to-metal ratio(up to H/M=2)and vastness of compositions.Although many studies reported rapid absorption kinetics,the investigation of hydrogen desorption is missing,especially in BCC HEAs.We have investigated the crystal structure,microstructure and hydrogen storage performance of a series of HEAs in the Ti-V-Nb-Cr system.Three types of TiVCrNb HEAs(Ti_(4)V_(3)NbCr_(2),Ti_(3)V_(3)Nb2Cr_(2),Ti_(2)V_(3)Nb_(3)Cr_(2))with close atomic radii and different valence electron concentrations(VECs)were designed with single BCC phase by CALPHAD method.The three alloys with fast hydrogen absorption kinetics reach the H/M ratio up to 2.Particularly,Ti_(4)V_(3)NbCr_(2)alloy shows the hydrogen storage capacity of 3.7 wt%,higher than other HEAs ever reported.The dehydrogenation activation energy of HEAs’hydride has been proved to decrease with decreasing VEC,which may be due to the weakening of alloy atom and H atom.Moreover,Ti_(4)V_(3)NbCr_(2)M(M=Mn,Fe,Ni)alloys were also synthesized to destabilize hydrides.The addition of Mn,Fe and Ni lead to precipitation of Laves phase,however,the kinetics did not improve further because of their own excellent hydrogen absorption.With increasing the content of Laves phase,there appear more pathways for hydrogen desorption so that the hydrides are more easily dissociated,which may provide new insights into how to achieve hydrogen desorption in BCC HEAs at room temperature.展开更多
To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature（T...To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature（Tx） not only induced nanoscale intermetallics to precipitate in the amorphous powder,but also increased Cu atomic percentage within the residual amorphous phase.Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase.Thus,a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling（the APMed powder）.The phase constituent in the APMed powder did not change during the post annealing,which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.展开更多
Acute Kidney Injury (AKI) is one of the most common acute and critical illnesses in general wards and intensive care units. Its high morbidity and high fatality rate have become a major global public health problem. T...Acute Kidney Injury (AKI) is one of the most common acute and critical illnesses in general wards and intensive care units. Its high morbidity and high fatality rate have become a major global public health problem. There are often serious lags in clinical diagnosis of AKI. Early diagnosis and timely intervention and effective care become critical. The use of electronic medical record data to build an AKI risk prediction model has been proven to help prevent the occurrence of AKI. However, in actual clinical applications, the distribution of historical data and new data will continue to vary over time, resulting in a significant decrease in the performance of the model. How to solve the problem of model performance degradation over time will be a core challenge for the long-term use of predictive models in clinical applications. Aiming at the above problems, this paper studies the classic Transfer-Stacking model migration algorithm. Aiming at the lack of this algorithm, such as the loss of a large amount of feature information of the target domain and poor fit when integrating the model of the target domain, the Accumulate-Transfer-Stacking algorithm is proposed to improve it. Improvements include: 1) Optimize the input vector and model integration algorithm of Transfer-Stacking’s target domain model. 2) Optimize Transfer-Stacking from a single-source domain model to a multi-source domain model. The experimental results show that for the improved algorithm proposed in this paper when the data is sufficient and insufficient, the average AUC value of the model on the data of subsequent years is 0.89 and 0.87, and the average F1 Score value is 0.45 and 0.36. Moreover, this method is significantly better than the unimproved Transfer-Stacking algorithm and baseline method, and can effectively overcome the problem of data distribution heterogeneity caused by time factors.展开更多
High-density coherent nanoprecipitates have been widely introduced into the design of new structural materials to achieve a superior strength-ductility balance.However,the thermal instability of nanostructures limits ...High-density coherent nanoprecipitates have been widely introduced into the design of new structural materials to achieve a superior strength-ductility balance.However,the thermal instability of nanostructures limits their fabrication and application.In this study,we investigated the temporal evolution of nanoprecipitates in coherent nanoprecipitation-strengthened Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2)high-entropy alloy during isothermal aging.When annealed at 600℃for more than 100 h,we found that its nanoprecipitates were invariably stable,with no obvious changes occurring in terms of morphology and distribution.The excellent stability was mainly attributed to the restricted state of interface migration and diffusion owing to the hierarchical nanostructure.The Cr-enriched nano-lamellar BCC phase divided the Cr-depleted FCC(L1_(2))matrix,forming barriers to long-range diffusion and resulting in a kinetically slow coarsening rate.As the nano-lamellar BCC phase spheroidized as the aging temperature increased to 700℃,the diffusion barriers were destroyed.Remarkable coarsening occurred after that,which further verified the significant effect of the nano-lamellar BCC phase on the microstructural stability.These results provide a paradigm for designing alloys stabilized via hierarchical nanostructure,achieving good strength-ductility synergy while excellent thermal stability.展开更多
Refractory high entropy alloys(RHEAs)have drawn much attention for their potential applications in ad-vanced reactors.While improved irradiation resistance to void swelling and helium bubble formation has been frequen...Refractory high entropy alloys(RHEAs)have drawn much attention for their potential applications in ad-vanced reactors.While improved irradiation resistance to void swelling and helium bubble formation has been frequently reported,experimental investigation regarding their early-stage irradiation damage re-mains insufficient,which hinders the understanding of the behavior of point defects and small clusters.Here we select two typical RHEAs with desired mechanical properties,VTaTi and HfNbZrTi,as well as a conventional V-4Cr-4Ti alloy,and compare their irradiation-induced defect production and hardening under a low-dose irradiation to~0.1 dpa.Significant hardening is observed in V-4Cr-4Ti due to the pin-ning of deformation-induced dislocations by the high density of irradiation-induced loops.In contrast,the hardening in VTaTi is much weaker,corresponding well to the greatly reduced defect density.Strikingly,in HfNbZrTi,visible defect clusters are not observed with a Cs-corrected transmission electron microscope in the whole irradiation range,and no hardening effect is detected.Such strong suppression of irradia-tion damage is attributed to the large lattice distortion based on the ab initio calculations and the local chemical fluctuations based on the atomic-scale elemental mappings,which together hinder the mobility of interstitials.Furthermore,minor irradiation softening is evidenced by cross-sectional nanoindentation tests in HfNbZrTi,which is considered to be related to the evolution of short-range orders and interstitial impurities after irradiation.展开更多
基金supported by the YEQISUN Joint Funds of the National Natural Science Foundation of China(Grant No.U2241234)the National Natural Science Foundation of China(Grant No.52301127).
文摘Premature adiabatic shear localization caused by strain softening is a roadblock for the application of body-centered cubic(BCC)structured high-entropy alloy(HEAs)in the impact field.A micron-scale orthorhombic-phase(O-phase)strengthened TiZrVNbAl alloy was developed to delay adiabatic shear failure and enhance dynamic ductility.The O-phase can not only reduce the slip length,but also promote the pinning and tangling of the dislocations near the phase boundaries.The introduction of the O-phase transformed the strain hardening rate from negative to positive,resulting in a significantly improved dynamic shear resistance.Meanwhile,slip transfer across the O-phase via dislocation cutting mechanisms and a reduction of slip band spacing guaranteed dynamic deformation uniformity.Benefiting from the introduction of the O-phase,the alloy exhibits an excellent stored energy density(∼446 J/cm^(3),surpass the reported BCC-HEAs and typical titanium alloys),a large dynamic fracture strain(∼42%)and a considerable dynamic specific yield strength(∼241 MPa cm^(3)g^(-1)).The present study presents an effective approach for developing BCC-HEAs with excellent dynamic shear resistance and plasticity.
基金support of the National Natural Science Foundation of China(Grant No.10872032)
文摘The dynamic tensile deformation and fracture behavior of the Zr-based metallic glass/porous W phase composite were investigated at room temperature by means of the Split Hopkinson Tension Bar （SHTB）.It was found that the composite exhibited no appreciable macroscopic plastic deformation prior to catastrophic fracture and the fracture surface was perpendicular to the axial direction.Substantive micro cracks were observed along the interface between W grains or the interface between the metallic glass phase and the W phase.Scanning electron microscopy （SEM） observations revealed that vein-like patterns,dimple-like patterns and substantive ridge-like structures were the typical fracture morphologies on the fracture surface for the metallic glass phase and the morphology of the W phase is a mixture of intergranular and transgranular fracture.Based on those results referred above,the dynamic tensile deformation and fracture mechanism of the Zr-based metallic glass/porous W phase composite were discussed in detail.
基金supported by the National Natural Science Foundation of China,China(Nos.51101018 and 51271036)
文摘Thermal residual stresses in W fibers/Zr-based metallic glass composites were measured by in situ high energy synchrotron X-ray diffraction(HEXRD). The W fibers for the composites were 300,500,and 700 m m in diameter,respectively. Coaxial cylinder model(CCM) and finite element model(FEM) were employed to simulate the distribution of thermal residual stress,respectively. HEXRD results showed that the selected diameters of W fiber had little influence on the value of thermal residual stresses in the present composites. Thermal residual stresses simulated by CCM and FEM were in good agreement with HEXRD measured results. In addition,FEM results exhibited that thermal residual stress concentrated on interface between the two phases and area where the two W fibers were the closest ones to each other.
基金financially supported by the National Natural Science Foundation of China(No.51901023)the National Key Research and Development Program of China(No.2018YFB0703400)。
文摘Liquid phase sintering(LPS)is a proven technique for preparing large-size tungsten heavy alloys(WHAs).However,for densification,this processing requires that the matrix of WHAs keeps melting for a long time,which simultaneously causes W grain coarsening that degenerates the performance.This work develops a novel ultrashort-time LPS method to form bulk high-performance fine-grain WHAs based on the principle of laser additive manufacturing(LAM).During LAM,the high-entropy alloy matrix(Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2))and W powders were fed simultaneously but only the matrix was melted by laser and most W particles remained solid,and the melted matrix rapidly solidified with laser moving away,producing an ultrashort-time LPS processing in the melt pool,i.e.,laser ultrashort-time liquid phase sintering(LULPS).The extreme short dwell time in liquid(-1/10,000 of conventional LPS)can effectively suppress W grain growth,obtaining a small size of 1/3 of the size in LPS WHAs.Meanwhile,strong convection in the melt pool of LULPS enables a nearly full densification in such a short sintering time.Compared with LPS WHAs,the LULPS fine-grain WHAs present a 42%higher yield strength,as well as an enhanced susceptibility to adiabatic shear banding(ASB)that is important for strong armor-piercing capability,indicating that LULPS can be a promising pathway for forming high-performance WHAs that surpass those prepared by conventional LPS.
基金National Natural Science Foundation of China(Grant Nos.51901004,52001025,and 52171060)State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China.
文摘Hot isostatic pressing(HIP)is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion(LPBF).In the present research,in order to improve the relative density and mechanical property,HIP was employed on the LPBF-processed Al-Cr-Fe-Ni-V high-entropy alloy(HEA)with microcracks and pores.The microstructure evolution and property improvement induced by HIP were investigated.In the LPBF-processed HEA,the microcracks were caused by residual stress and element segregation,and these microcracks as well as the pores reduced significantly after HIP treatments.Remarkably,HIP temperature has a more critical effect on the microcrack closure than the holding time,thus,microcracks and pores still existed after HIP-1 treatment(1273 K,8 h),while HIP-2 treatment(1473 K,4 h)could close the microcracks significantly.The crack closure was attributed to the interfacial diffusion of the alloying element under high temperature accompanied by high pressure,and the degree of element diffusion at both interfaces of the cracks determined the bonding strength after crack closure.Higher temperatures at high pressure induced more adequate element diffusion and higher bonding strength.The above high temperature and high pressure also induced the growth of the L1_(2) phase and the precipitation of the B2 phase in HEA.Consequently,the tensile strength and elonga-tion of the LPBF-processed HEA after HIP-2 treatment were simultaneously enhanced(80.7%and 222.5%higher than that of LPBF-processed HEA,respectively).This could be attributed to the combined effect of microcrack/pore closure and precipitation strengthening.The strengthening effect of the B2 phase and L1_(2) phase accounted for 53%(dislocation by-pass mechanism)and 47%(dislocation shearing mechanism)of the total precipitation strengthening,respectively.
基金This work was financially supported by the National Natural Science Foundation of China(No.51701018)the National Key Research and Development Program of China(No.2018YFB0703400).
文摘Recently,high-entropy alloys(HEAs)designed by the concepts of unique entropy-stabilized mechanisms,started to attract widespread interests for their hydrogen storage properties.HEAs with body-centered cubic(BCC)structures present a high potential for hydrogen storage due to the high hydrogen-to-metal ratio(up to H/M=2)and vastness of compositions.Although many studies reported rapid absorption kinetics,the investigation of hydrogen desorption is missing,especially in BCC HEAs.We have investigated the crystal structure,microstructure and hydrogen storage performance of a series of HEAs in the Ti-V-Nb-Cr system.Three types of TiVCrNb HEAs(Ti_(4)V_(3)NbCr_(2),Ti_(3)V_(3)Nb2Cr_(2),Ti_(2)V_(3)Nb_(3)Cr_(2))with close atomic radii and different valence electron concentrations(VECs)were designed with single BCC phase by CALPHAD method.The three alloys with fast hydrogen absorption kinetics reach the H/M ratio up to 2.Particularly,Ti_(4)V_(3)NbCr_(2)alloy shows the hydrogen storage capacity of 3.7 wt%,higher than other HEAs ever reported.The dehydrogenation activation energy of HEAs’hydride has been proved to decrease with decreasing VEC,which may be due to the weakening of alloy atom and H atom.Moreover,Ti_(4)V_(3)NbCr_(2)M(M=Mn,Fe,Ni)alloys were also synthesized to destabilize hydrides.The addition of Mn,Fe and Ni lead to precipitation of Laves phase,however,the kinetics did not improve further because of their own excellent hydrogen absorption.With increasing the content of Laves phase,there appear more pathways for hydrogen desorption so that the hydrides are more easily dissociated,which may provide new insights into how to achieve hydrogen desorption in BCC HEAs at room temperature.
基金supported by the National Natural Science Foundation of China(Grant Nos.51271036 and 51471035)
文摘To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder,structural modification of the amorphous powder was performed through annealing and post milling.Annealing above the crystallization temperature（Tx） not only induced nanoscale intermetallics to precipitate in the amorphous powder,but also increased Cu atomic percentage within the residual amorphous phase.Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase.Thus,a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling（the APMed powder）.The phase constituent in the APMed powder did not change during the post annealing,which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.
文摘Acute Kidney Injury (AKI) is one of the most common acute and critical illnesses in general wards and intensive care units. Its high morbidity and high fatality rate have become a major global public health problem. There are often serious lags in clinical diagnosis of AKI. Early diagnosis and timely intervention and effective care become critical. The use of electronic medical record data to build an AKI risk prediction model has been proven to help prevent the occurrence of AKI. However, in actual clinical applications, the distribution of historical data and new data will continue to vary over time, resulting in a significant decrease in the performance of the model. How to solve the problem of model performance degradation over time will be a core challenge for the long-term use of predictive models in clinical applications. Aiming at the above problems, this paper studies the classic Transfer-Stacking model migration algorithm. Aiming at the lack of this algorithm, such as the loss of a large amount of feature information of the target domain and poor fit when integrating the model of the target domain, the Accumulate-Transfer-Stacking algorithm is proposed to improve it. Improvements include: 1) Optimize the input vector and model integration algorithm of Transfer-Stacking’s target domain model. 2) Optimize Transfer-Stacking from a single-source domain model to a multi-source domain model. The experimental results show that for the improved algorithm proposed in this paper when the data is sufficient and insufficient, the average AUC value of the model on the data of subsequent years is 0.89 and 0.87, and the average F1 Score value is 0.45 and 0.36. Moreover, this method is significantly better than the unimproved Transfer-Stacking algorithm and baseline method, and can effectively overcome the problem of data distribution heterogeneity caused by time factors.
基金supported by the National Na-ture Science Foundation of China(Nos.U2241234,52201152,and 52301127)the China Postdoctoral Science Foundation(No.2022M720150)the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of En-ergy(No.DE-AC02-06CH11357).
文摘High-density coherent nanoprecipitates have been widely introduced into the design of new structural materials to achieve a superior strength-ductility balance.However,the thermal instability of nanostructures limits their fabrication and application.In this study,we investigated the temporal evolution of nanoprecipitates in coherent nanoprecipitation-strengthened Al_(0.5)Cr_(0.9)FeNi_(2.5)V_(0.2)high-entropy alloy during isothermal aging.When annealed at 600℃for more than 100 h,we found that its nanoprecipitates were invariably stable,with no obvious changes occurring in terms of morphology and distribution.The excellent stability was mainly attributed to the restricted state of interface migration and diffusion owing to the hierarchical nanostructure.The Cr-enriched nano-lamellar BCC phase divided the Cr-depleted FCC(L1_(2))matrix,forming barriers to long-range diffusion and resulting in a kinetically slow coarsening rate.As the nano-lamellar BCC phase spheroidized as the aging temperature increased to 700℃,the diffusion barriers were destroyed.Remarkable coarsening occurred after that,which further verified the significant effect of the nano-lamellar BCC phase on the microstructural stability.These results provide a paradigm for designing alloys stabilized via hierarchical nanostructure,achieving good strength-ductility synergy while excellent thermal stability.
基金supported by the National MCF En-ergy R&D Program of China(No.2022YFE03120000)the Na-tional Natural Science Foundation of China(Nos.12375266 and 12435016).
文摘Refractory high entropy alloys(RHEAs)have drawn much attention for their potential applications in ad-vanced reactors.While improved irradiation resistance to void swelling and helium bubble formation has been frequently reported,experimental investigation regarding their early-stage irradiation damage re-mains insufficient,which hinders the understanding of the behavior of point defects and small clusters.Here we select two typical RHEAs with desired mechanical properties,VTaTi and HfNbZrTi,as well as a conventional V-4Cr-4Ti alloy,and compare their irradiation-induced defect production and hardening under a low-dose irradiation to~0.1 dpa.Significant hardening is observed in V-4Cr-4Ti due to the pin-ning of deformation-induced dislocations by the high density of irradiation-induced loops.In contrast,the hardening in VTaTi is much weaker,corresponding well to the greatly reduced defect density.Strikingly,in HfNbZrTi,visible defect clusters are not observed with a Cs-corrected transmission electron microscope in the whole irradiation range,and no hardening effect is detected.Such strong suppression of irradia-tion damage is attributed to the large lattice distortion based on the ab initio calculations and the local chemical fluctuations based on the atomic-scale elemental mappings,which together hinder the mobility of interstitials.Furthermore,minor irradiation softening is evidenced by cross-sectional nanoindentation tests in HfNbZrTi,which is considered to be related to the evolution of short-range orders and interstitial impurities after irradiation.
