Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys...Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys(HEAs)are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability.Herein,we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure.This is accomplished by introducing high-density coherent L1_(2) nanoprecipitates.Multiscale characterization and molecular dynamics simulation demonstrate that the L1_(2) nanoprecipitates exhibit multiple functions during impact,not only as the dislocation barrier and the dislocation transmission medium,but also as energyabsorbing islands that disperse the stress spikes through order-to-disorder transition,which result in extraordinary impact resistance.These findings shed light on the development of novel impact-resistant metallic materials.展开更多
Based on the actual conditions of laser powder bed fusion(LPBF),a three-dimensional transient thermal-structural coupling single-layer finite element model was established to simulate the LPBF of Al-Cu-Mg-Si alloys.Af...Based on the actual conditions of laser powder bed fusion(LPBF),a three-dimensional transient thermal-structural coupling single-layer finite element model was established to simulate the LPBF of Al-Cu-Mg-Si alloys.After characterizing the thermal behavior and residual stress distribution of the molten pool under different LPBF parameters,the cracking mechanisms of the Al-Cu-Mg-Si alloy were revealed.With an increase in the number of scanning tracks,the maximum cooling rate decreased gradually,whereas the maximum heating rate first increased and then decreased.The residual stress of the printed parts after cooling was primarily tensile stress.The residual stress along the scanning direction was mainly distributed in the center of the printing layer,whereas the residual stress perpendicular to the scanning direction was mainly concentrated in the center of the track.The residual stress along the deposition direction decreased with increasing distance from the substrate,with the highest stress occurring at the contact position with the substrate.Compared with the scanning speed,the laser power had a greater effect on the temperature and residual stress.The reliability of the numerical simulation was verified based on the size of the molten pool and the direction of crack propagation.展开更多
Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be ...Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be attributed to the multiple deformation mechanisms,including dislocation slip,deformation induced stacking fault and mechanical twinning.The shear localization behavior of the FeCrNi MEA was also analyzed by dynamically loading hat-shaped specimens,and the distinct adiabatic shear band cannot be observed until the shear strain reaches~14.5.The microstructures within and outside the shear band exhibit different characteristics:the grains near the shear band are severely elongated and significantly refined by dislocation slip and twinning;inside the shear band,the initial coarse grains completely disappear,and transform into recrystallized ultrafine equiaxed grains by the classical rotational dynamic recrystallization mechanism.Moreover,microvoids preferentially nucleate in the central areas of the shear band where the temperature is very high and the shear stress is highly concentrated.These microvoids will coalesce into microcracks with the increase of strain,which eventually leads to the fracture of the shear band.展开更多
The mechanical properties of refractory high entropy alloys(RHEAs) strongly depend on their phase structures. In this work, the phase stability of a BCC TiNbTa0.5ZrAl0.5 refractory high entropy alloy subjected to ther...The mechanical properties of refractory high entropy alloys(RHEAs) strongly depend on their phase structures. In this work, the phase stability of a BCC TiNbTa0.5ZrAl0.5 refractory high entropy alloy subjected to thermomechanical processing was evaluated, and the effects of phase decomposition on room/high temperature mechanical properties were quantitatively studied. It was found that, the thermomechanical processing at 800℃and 1200℃ leads to phase decomposition in the TiNbTa0.5ZrAl0.5 alloy. The phase decomposition is caused by the rapid rising of free energy of the primary BCC phase. The effect of the precipitates on room temperature strength is determined by the competition between the increasing in precipitation strengthening and the decreasing in solid solution strengthening. But at high temperatures(800-1200℃), the phase decomposition causes significant reduction in strength, mainly due to the grain boundary sliding and the decreasing in solid solution strengthening.展开更多
A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single...A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single face-centered cubic(FCC)matrix,in which highly dispersed oxide nanoparticles,including Y_(2)Ti_(2)O_(7),Y_(2)TiO_(5) and Y_(2)O_(3),are uniformly distributed.Compared with the FeCrNi MEA,the ODS FeCrNi MEA exhibits the improved yield strength(1120 MPa)and ultimate tensile strength(1274 MPa)with adequate ductility retention(12.1%).Theoretical analysis of the strengthening mechanism indicates that the high strength is mainly attributed to the grain-boundary strengthening caused by fine grains and the precipitation strengthening resulted from the oxide nanoparticles.Meanwhile,the matrix that easily activates mechanical twinning during the deformation process is the main reason to ensure moderate ductility.In addition,the introduction of high-density oxide nanoparticles can disperse the defect distri-bution and suppress the defect growth and irradiation-induced segregation,leading to the excellent irra-diation resistance.These findings provide innovative guidance for the development of high-performance structural materials for future nuclear energy applications with balanced strength and ductility.展开更多
Additive manufacturing is believed to open up a new era in precise microfabrication,and the dynamic microstructure evolution during the process as well as the experiment-simulation correlated study is conducted on a p...Additive manufacturing is believed to open up a new era in precise microfabrication,and the dynamic microstructure evolution during the process as well as the experiment-simulation correlated study is conducted on a prototype multi-principal-element alloys FeCrNi fabricated using selective laser melting(SLM).Experimental results reveal that columnar crystals grow across the cladding layers and the dense cellular structures develop in the filled crystal.At the micron scale,all constituent elements are evenly distributed,while at the near-atomic scale,Cr element is obviously segregated.Simulation results at the atomic scale illustrate that i)the solid-liquid interface during the grain growth changes from horizontal to arc due to the radial temperature gradient;ii)the precipitates,microscale voids,and stacking faults also form dynamically as a result of the thermal gradient,leading to the residual stress in the SLMed structure.In addition,we established a microstructure-based physical model based on atomic simulation,which indicates that strong interface strengthening exists in the tensile deformation.The present work provides an atomic-scale understanding of the microstructural evolution in the SLM process through the combination of experiment and simulation.展开更多
Background and Aims:Patients with hepatocellular carci-noma(HCC)surgically resected are at risk of recurrence;however,the risk factors of recurrence remain poorly un-derstood.This study intended to establish a novel m...Background and Aims:Patients with hepatocellular carci-noma(HCC)surgically resected are at risk of recurrence;however,the risk factors of recurrence remain poorly un-derstood.This study intended to establish a novel machine learning model based on clinical data for predicting early re-currence of HCC after resection.Methods:A total of 220 HCC patients who underwent resection were enrolled.Clas-sification machine learning models were developed to predict HCC recurrence.The standard deviation,recall,and preci-sion of the model were used to assess the model’s accura-cy and identify efficiency of the model.Results:Recurrent HCC developed in 89(40.45%)patients at a median time of 14 months from primary resection.In principal compo-nent analysis,tumor size,tumor grade differentiation,por-tal vein tumor thrombus,alpha-fetoprotein,protein induced by vitamin K absence or antagonist-II(PIVKA-II),aspartate aminotransferase,platelet count,white blood cell count,and HBsAg were positive prognostic factors of HCC recurrence and were included in the preoperative model.After compar-ing different machine learning methods,including logistic re-gression,decision tree,naïve Bayes,deep neural networks,and k-nearest neighbor(K-NN),we choose the K-NN model as the optimal prediction model.The accuracy,recall,preci-sion of the K-NN model were 70.6%,51.9%,70.1%,respec-tively.The standard deviation was 0.020.Conclusions:The K-NN classification algorithm model performed better than the other classification models.Estimation of the recurrence rate of early HCC can help to allocate treatment,eventually achieving safe oncological outcomes.展开更多
基金the National Natural Science Foundation of China(Grant No.52020105013 and 52401223)Natural Science Foundation of Hunan Province(Grant No.2022JJ20001)+1 种基金Science and Technology Foundation Strengthening Program(Grant No.6142902210104)T.Y.is grateful for the financial support from the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant No.C1020-21G).
文摘Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys(HEAs)are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability.Herein,we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure.This is accomplished by introducing high-density coherent L1_(2) nanoprecipitates.Multiscale characterization and molecular dynamics simulation demonstrate that the L1_(2) nanoprecipitates exhibit multiple functions during impact,not only as the dislocation barrier and the dislocation transmission medium,but also as energyabsorbing islands that disperse the stress spikes through order-to-disorder transition,which result in extraordinary impact resistance.These findings shed light on the development of novel impact-resistant metallic materials.
基金supported by National Natural Science Foundation of China(Grant Nos.52071299,51804280)Special Fund for Science and Technology Innovation Teams of Shanxi Province,China(Grant No.202304051001029)+3 种基金Major Science and Technology Projects of Shanxi Province,China(Grant Nos.20181101009,20201102009)Scientific and Technological Achievements Transformation Guidance Project of Shanxi Province,China(Grant No.202204021301048)Fundamental Research Program of Shanxi Province,China(Grant No.202203021212117)Young Elite Scientists Sponsorship Program by CAST(Grant No.2023QNRC001)。
文摘Based on the actual conditions of laser powder bed fusion(LPBF),a three-dimensional transient thermal-structural coupling single-layer finite element model was established to simulate the LPBF of Al-Cu-Mg-Si alloys.After characterizing the thermal behavior and residual stress distribution of the molten pool under different LPBF parameters,the cracking mechanisms of the Al-Cu-Mg-Si alloy were revealed.With an increase in the number of scanning tracks,the maximum cooling rate decreased gradually,whereas the maximum heating rate first increased and then decreased.The residual stress of the printed parts after cooling was primarily tensile stress.The residual stress along the scanning direction was mainly distributed in the center of the printing layer,whereas the residual stress perpendicular to the scanning direction was mainly concentrated in the center of the track.The residual stress along the deposition direction decreased with increasing distance from the substrate,with the highest stress occurring at the contact position with the substrate.Compared with the scanning speed,the laser power had a greater effect on the temperature and residual stress.The reliability of the numerical simulation was verified based on the size of the molten pool and the direction of crack propagation.
基金supported by the National Natural Science Foundation of China[Grant numbers 52020105013,51771232]。
文摘Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be attributed to the multiple deformation mechanisms,including dislocation slip,deformation induced stacking fault and mechanical twinning.The shear localization behavior of the FeCrNi MEA was also analyzed by dynamically loading hat-shaped specimens,and the distinct adiabatic shear band cannot be observed until the shear strain reaches~14.5.The microstructures within and outside the shear band exhibit different characteristics:the grains near the shear band are severely elongated and significantly refined by dislocation slip and twinning;inside the shear band,the initial coarse grains completely disappear,and transform into recrystallized ultrafine equiaxed grains by the classical rotational dynamic recrystallization mechanism.Moreover,microvoids preferentially nucleate in the central areas of the shear band where the temperature is very high and the shear stress is highly concentrated.These microvoids will coalesce into microcracks with the increase of strain,which eventually leads to the fracture of the shear band.
基金financially supported by the National Natural Science Funds for Distinguished Young Scholar of China (No. 51625404)the National Natural Science Foundation of China (No. 51671217)。
文摘The mechanical properties of refractory high entropy alloys(RHEAs) strongly depend on their phase structures. In this work, the phase stability of a BCC TiNbTa0.5ZrAl0.5 refractory high entropy alloy subjected to thermomechanical processing was evaluated, and the effects of phase decomposition on room/high temperature mechanical properties were quantitatively studied. It was found that, the thermomechanical processing at 800℃and 1200℃ leads to phase decomposition in the TiNbTa0.5ZrAl0.5 alloy. The phase decomposition is caused by the rapid rising of free energy of the primary BCC phase. The effect of the precipitates on room temperature strength is determined by the competition between the increasing in precipitation strengthening and the decreasing in solid solution strengthening. But at high temperatures(800-1200℃), the phase decomposition causes significant reduction in strength, mainly due to the grain boundary sliding and the decreasing in solid solution strengthening.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52020105013 and 52104365)the US National Science Foundation(Nos.DMR 1611180 and 1809640)with program directors,Drs.J.Yang,G.Shiflet,and D.Farkas.
文摘A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single face-centered cubic(FCC)matrix,in which highly dispersed oxide nanoparticles,including Y_(2)Ti_(2)O_(7),Y_(2)TiO_(5) and Y_(2)O_(3),are uniformly distributed.Compared with the FeCrNi MEA,the ODS FeCrNi MEA exhibits the improved yield strength(1120 MPa)and ultimate tensile strength(1274 MPa)with adequate ductility retention(12.1%).Theoretical analysis of the strengthening mechanism indicates that the high strength is mainly attributed to the grain-boundary strengthening caused by fine grains and the precipitation strengthening resulted from the oxide nanoparticles.Meanwhile,the matrix that easily activates mechanical twinning during the deformation process is the main reason to ensure moderate ductility.In addition,the introduction of high-density oxide nanoparticles can disperse the defect distri-bution and suppress the defect growth and irradiation-induced segregation,leading to the excellent irra-diation resistance.These findings provide innovative guidance for the development of high-performance structural materials for future nuclear energy applications with balanced strength and ductility.
基金supported by the National Natural Science Foundation of China(Nos.52020105013,51871092,and 11902113)the Natural Science Foundation of Hunan Province(Nos.2019JJ50068 and 2021JJ40032)+1 种基金the Changsha Municipal Natu-ral Science Foundation(No.kq2014126)support from the National Science Foundation(Nos.DMR-1611180 and 1809640).
文摘Additive manufacturing is believed to open up a new era in precise microfabrication,and the dynamic microstructure evolution during the process as well as the experiment-simulation correlated study is conducted on a prototype multi-principal-element alloys FeCrNi fabricated using selective laser melting(SLM).Experimental results reveal that columnar crystals grow across the cladding layers and the dense cellular structures develop in the filled crystal.At the micron scale,all constituent elements are evenly distributed,while at the near-atomic scale,Cr element is obviously segregated.Simulation results at the atomic scale illustrate that i)the solid-liquid interface during the grain growth changes from horizontal to arc due to the radial temperature gradient;ii)the precipitates,microscale voids,and stacking faults also form dynamically as a result of the thermal gradient,leading to the residual stress in the SLMed structure.In addition,we established a microstructure-based physical model based on atomic simulation,which indicates that strong interface strengthening exists in the tensile deformation.The present work provides an atomic-scale understanding of the microstructural evolution in the SLM process through the combination of experiment and simulation.
基金National Natural Science Fund(No.8197054582170609)+1 种基金Natural Science Foundation of Shandong Province(Major Project)(No.ZR2020KH006)Ji’nan Science and Technology Development Project(No.2020190790).
文摘Background and Aims:Patients with hepatocellular carci-noma(HCC)surgically resected are at risk of recurrence;however,the risk factors of recurrence remain poorly un-derstood.This study intended to establish a novel machine learning model based on clinical data for predicting early re-currence of HCC after resection.Methods:A total of 220 HCC patients who underwent resection were enrolled.Clas-sification machine learning models were developed to predict HCC recurrence.The standard deviation,recall,and preci-sion of the model were used to assess the model’s accura-cy and identify efficiency of the model.Results:Recurrent HCC developed in 89(40.45%)patients at a median time of 14 months from primary resection.In principal compo-nent analysis,tumor size,tumor grade differentiation,por-tal vein tumor thrombus,alpha-fetoprotein,protein induced by vitamin K absence or antagonist-II(PIVKA-II),aspartate aminotransferase,platelet count,white blood cell count,and HBsAg were positive prognostic factors of HCC recurrence and were included in the preoperative model.After compar-ing different machine learning methods,including logistic re-gression,decision tree,naïve Bayes,deep neural networks,and k-nearest neighbor(K-NN),we choose the K-NN model as the optimal prediction model.The accuracy,recall,preci-sion of the K-NN model were 70.6%,51.9%,70.1%,respec-tively.The standard deviation was 0.020.Conclusions:The K-NN classification algorithm model performed better than the other classification models.Estimation of the recurrence rate of early HCC can help to allocate treatment,eventually achieving safe oncological outcomes.
