A simple chemical-etching approach is used to prepare the silicon carbide quantum dots (QDs). The raw materials of silicon carbide (SiC) with homogeneous nanoparticles fabricated via self-propagating combustion synthe...A simple chemical-etching approach is used to prepare the silicon carbide quantum dots (QDs). The raw materials of silicon carbide (SiC) with homogeneous nanoparticles fabricated via self-propagating combustion synthesis are corroded in mixture etchants of nitric and hydrofluoric acid. After sonication and chromatography in the ultra-gravity field for the etched products, aqueous solution with QDs can be obtained. The microstructure evolution of raw particles and optical properties of QDs were measured. Different organophilic groups on the surface like carboxyl, oxygroup, and hyfroxy were produced in the process of etching. Fluorescent labeling and imaging for living cells of Aureobasidium pulluans were investigated. The results indicated that SiC QDs were not cytotoxic and could stably label due to the conjugation between organophilic groups of QDs and specific protein of cells, it can be utilized for fluorescent imaging and tracking cells with in vivo and long-term-distance. Moreover, mechanism and specificity of mark were also analyzed.展开更多
The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic defo...The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic deformation increases as the revolutions increase along the radial direction on the transversal plane of disks. In addition, the hardness and the microstructure distributions verify the trend that the effective strain of the HPT processed disks at the early torsion stage is gradually deformed from the edge to the center with the revolutions increases.展开更多
Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at...Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at room temperature.Electroplasticity of the Al_(0.6) CoCrFeNiMn HEA was studied systematically using electrically assisted uniaxial tension.The results showed that pulse current caused the temperature gradient along the tensile direction and the temperatures of the samples increased with the current den-sity.The flow stress decreased,and the elongation increased with increasing current density during the EAD.When the current density was 30 A mm-2,the total elongation of the samples could be increased by 50%compared to that with no pulse.Pulse current can reduce local stress concentration and post-pone microcracks initiation in the body-centered cubic(BCC)phases,and hence can effectively inhibit cracks and ruptures.The dislocation tangles were opened by pulse current,and the dislocation recovery was enhanced at a high current density.Compared with dilute solid solution alloys,the lattice distortion effect,the high fraction of the BCC phases,and the dislocations in HEAs can lead to the enhancement of the local Joule heating,which accelerated dislocation slip and dislocation annihilation.This study con-firms that EAD can effectively im prove the formability of HEAs and provides theoretical guidance and an experimental basis for forming HEAs components.展开更多
A neural network model is developed to search vast compositional space of high entropy alloys(HEAs).The model predicts the mechanical properties of HEAs better than several other models.It’s because the special struc...A neural network model is developed to search vast compositional space of high entropy alloys(HEAs).The model predicts the mechanical properties of HEAs better than several other models.It’s because the special structure of the model helps the model understand the characteristics of constituent elements of HEAs.In addition,thermodynamics descriptors were utilized as input to the model so that the model predicts better by understanding the thermodynamic properties of HEAs.A conditional random search,which is good at finding local optimal values,was selected as the inverse predictor and designed two HEAs using the model.We experimentally verified that the HEAs have the best combination of strength and ductility and this proves the validity of the model and alloy design method.The strengthening mechanism of the designed HEAs is further discussed based on microstructure and lattice distortion effect.The present alloy design approach,specialized in finding multiple local optima,could help researchers design an infinite number of new alloys with interesting properties.展开更多
The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in orde...The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.展开更多
Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy.One of the possible factors that contribute to twinning origination from grain boundaries is th...Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy.One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation.Nonetheless,the influence of mechanical interaction among grains on twin evolution has not been fully understood.In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior,a clear relation among the large aggregate of grains is still lacking.In this work,we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature.Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building.Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation.Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.展开更多
We present a new class of metastable high-entropy alloys(HEAs),triggering deformation-induced martensitic transformation(DIMT)from face-centered-cubic(FCC)to body-centered-cubic(BCC),i.e.,BCC-DIMT.Through the ab-initi...We present a new class of metastable high-entropy alloys(HEAs),triggering deformation-induced martensitic transformation(DIMT)from face-centered-cubic(FCC)to body-centered-cubic(BCC),i.e.,BCC-DIMT.Through the ab-initio calculation based on 1 st order axial interaction model and combined with the Gibbs free energy calculation,the addition of Si is considered as a critical element which enables to reduce the intrinsic stacking fault energy(ISFE)in Si_xV_((9-x))Cr_(10)Mn_5 Fe_(46)Co_(30)(x=2,4,and 7 at.%)alloy system.The ISFE decreases from-30.4 to-35.5 mJ/m^(2)as the Si content increases from 2 to 7 at.%,which well corresponds to the reduced phase stability of FCC against HCP.The BCC-DIMT occurs in all the alloys via intermediate HCP martensite,and the HCP martensite provides nucleation sites of BCC martensite.Therefore,the transformation rate enhances as the Si content increases in an earlier deformation ra nge.However,the BCC-DIMT is also affected by the phase stability of FCC against BCC,and the stability is the highest at the Si content of 7 at.%.Thus,the 7Si alloy presents the moderate transformation rate in the later deformation range.Due to the well-controlled transformation rate and consequent strain-ha rdening rate,the 7Si alloy possesses the superior combination of strength and ductility beyond 1 GPa of tensile strength at room temperature.Our results suggest that the Si addition can be a favorable candidate in various metastable HEAs for the further property improvement.展开更多
The digitized format of microstructures,or digital microstructures,plays a crucial role in modern-day materials research.Unfortunately,the acquisition of digital microstructures through experimental means can be unsuc...The digitized format of microstructures,or digital microstructures,plays a crucial role in modern-day materials research.Unfortunately,the acquisition of digital microstructures through experimental means can be unsuccessful in delivering sufficient resolution that is necessary to capture all relevant geometric features of the microstructures.The resolution-sensitive microstructural features overlooked due to insufficient resolution may limit one’s ability to conduct a thorough microstructure characterization and material behavior analysis such as mechanical analysis based on numerical modeling.Here,a highly efficient super-resolution imaging based on deep learning is developed using a deep super-resolution residual network to super-resolved low-resolution(LR)microstructure data for microstructure characterization and finite element(FE)mechanical analysis.Microstructure characterization and FE model based mechanical analysis using the super-resolved microstructure data not only proved to be as accurate as those based on high-resolution(HR)data but also provided insights on local microstructural features such as grain boundary normal and local stress distribution,which can be only partially considered or entirely disregarded in LR data-based analysis.展开更多
Fullerene-reinforced A1 matrix nanocomposites were fabricated by high-energy mechanical milling followed by consolidation through hot extrusion or high-pressure torsion(HPT). The results indicate that a relatively hom...Fullerene-reinforced A1 matrix nanocomposites were fabricated by high-energy mechanical milling followed by consolidation through hot extrusion or high-pressure torsion(HPT). The results indicate that a relatively homogeneous microstructure consisting of elongated, micrometer-sized A1 grains is formed in the hot-extruded specimens. However, the microstructure is not uniform along the radius of the HPT disks, which includes coarse grains near the center of the disk and ultrafine grains in the middle and along the edge of the specimen. Microstructural evaluations of the HPT disks indicate that A1 grain refinement occurs due to the addition of fullerene, as grain size is reduced to 60 nm from 118 nm. The formation of the harmful aluminum carbide phase is not detected during the fabrication of Al/C_(60) nanocomposites. The hardness, yield stress, and ultimate tensile strength of the Al-2 vol.% C_(60) nanocomposites are about 27-160% higher than those of the monolithic A1 samples, revealing the effective strengthening of fullerene particles in A1 matrix. Moreover,mechanical properties of the Al/fullerene nanocomposites are significantly enhanced(59-272%) by utilizing HPT in comparison to hot-extruded specimens due to their much finer A1 grain structure. The reduction in the number and the size of the dimples, as well as the formation of smooth regions on the tensile fracture surface of Al/C_(60), results in their overall lower ductility compared to monolithic Al.展开更多
In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations ...In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF) life of this alloy.A thermomechanical process was applied to induce fine-grained(FG) and coarse-grained(CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C(atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.展开更多
文摘A simple chemical-etching approach is used to prepare the silicon carbide quantum dots (QDs). The raw materials of silicon carbide (SiC) with homogeneous nanoparticles fabricated via self-propagating combustion synthesis are corroded in mixture etchants of nitric and hydrofluoric acid. After sonication and chromatography in the ultra-gravity field for the etched products, aqueous solution with QDs can be obtained. The microstructure evolution of raw particles and optical properties of QDs were measured. Different organophilic groups on the surface like carboxyl, oxygroup, and hyfroxy were produced in the process of etching. Fluorescent labeling and imaging for living cells of Aureobasidium pulluans were investigated. The results indicated that SiC QDs were not cytotoxic and could stably label due to the conjugation between organophilic groups of QDs and specific protein of cells, it can be utilized for fluorescent imaging and tracking cells with in vivo and long-term-distance. Moreover, mechanism and specificity of mark were also analyzed.
文摘The effect of revolution on inhomogeneous plastic deformation of HPT processed IF steel was investigated using experimental and simulation approaches. The results indicate that the degree of inhomogeneous plastic deformation increases as the revolutions increase along the radial direction on the transversal plane of disks. In addition, the hardness and the microstructure distributions verify the trend that the effective strain of the HPT processed disks at the early torsion stage is gradually deformed from the edge to the center with the revolutions increases.
基金financially supported by the National Natural Science Foundation of China(No.51635005)the National Re-search Foundation of Korea(NRF)grant funded by the Korea gov-ernment(MSIP)(No.NRF-2021R1A2C3006662)supported by the China Scholarship Council(CSC,No.202106120151).
文摘Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at room temperature.Electroplasticity of the Al_(0.6) CoCrFeNiMn HEA was studied systematically using electrically assisted uniaxial tension.The results showed that pulse current caused the temperature gradient along the tensile direction and the temperatures of the samples increased with the current den-sity.The flow stress decreased,and the elongation increased with increasing current density during the EAD.When the current density was 30 A mm-2,the total elongation of the samples could be increased by 50%compared to that with no pulse.Pulse current can reduce local stress concentration and post-pone microcracks initiation in the body-centered cubic(BCC)phases,and hence can effectively inhibit cracks and ruptures.The dislocation tangles were opened by pulse current,and the dislocation recovery was enhanced at a high current density.Compared with dilute solid solution alloys,the lattice distortion effect,the high fraction of the BCC phases,and the dislocations in HEAs can lead to the enhancement of the local Joule heating,which accelerated dislocation slip and dislocation annihilation.This study con-firms that EAD can effectively im prove the formability of HEAs and provides theoretical guidance and an experimental basis for forming HEAs components.
基金This work has been financially supported by the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT,Korea(2016M3D1A1023383 and NRF-2022R1A5A1030054).Also,special thanks to Dr.Hyun-Seok Do(Department of Materials Science and Engineering,POSTECH,Republic of Korea)for the upgrade of the 2NN MEAM interatomic potentials.
文摘A neural network model is developed to search vast compositional space of high entropy alloys(HEAs).The model predicts the mechanical properties of HEAs better than several other models.It’s because the special structure of the model helps the model understand the characteristics of constituent elements of HEAs.In addition,thermodynamics descriptors were utilized as input to the model so that the model predicts better by understanding the thermodynamic properties of HEAs.A conditional random search,which is good at finding local optimal values,was selected as the inverse predictor and designed two HEAs using the model.We experimentally verified that the HEAs have the best combination of strength and ductility and this proves the validity of the model and alloy design method.The strengthening mechanism of the designed HEAs is further discussed based on microstructure and lattice distortion effect.The present alloy design approach,specialized in finding multiple local optima,could help researchers design an infinite number of new alloys with interesting properties.
基金supported by the Learning & Academic Research Institution for Master’s and Ph.D. Students and Postdocs (LAMP) Program of the National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (No. RS-2023-00285353)supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF-2021R1A2C3006662, NRF-2022R1A5A1030054, and 2021R1A2C1091301)+3 种基金the support from Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Foundation for Innovation (CFI)Atlantic Canada Opportunities Agency (ACOA)the New Brunswick Innovation Foundation (NBIF)
文摘The ex-situ incorporation of the secondary SiC reinforcement,along with the in-situ incorporation of the tertiary and quaternary Mg_(3)N_(2) and Si_(3)N_(4) phases,in the primary matrix of Mg_(2)Si is employed in order to provide ultimate wear resistance based on the laser-irradiation-induced inclusion of N_(2) gas during laser powder bed fusion.This is substantialized based on both the thermal diffusion-and chemical reactionbased metallurgy of the Mg_(2)Si–SiC/nitride hybrid composite.This study also proposes a functional platform for systematically modulating a functionally graded structure and modeling build-direction-dependent architectonics during additive manufacturing.This strategy enables the development of a compositional gradient from the center to the edge of each melt pool of the Mg_(2)Si–SiC/nitride hybrid composite.Consequently,the coefficient of friction of the hybrid composite exhibits a 309.3%decrease to–1.67 compared to–0.54 for the conventional nonreinforced Mg_(2)Si structure,while the tensile strength exhibits a 171.3%increase to 831.5 MPa compared to 485.3 MPa for the conventional structure.This outstanding mechanical behavior is due to the(1)the complementary and synergistic reinforcement effects of the SiC and nitride compounds,each of which possesses an intrinsically high hardness,and(2)the strong adhesion of these compounds to the Mg_(2)Si matrix despite their small sizes and low concentrations.
基金supported by POSCO(2015Y073)Brain Korea 21 PLUS project for Center for Creative Industrial Materials(F16SN25D1706)National Research Foundation of Korea(NRF)grant funded by the Korean government(MISP)(No.2014R1A2A1A10051322).
文摘Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy.One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation.Nonetheless,the influence of mechanical interaction among grains on twin evolution has not been fully understood.In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior,a clear relation among the large aggregate of grains is still lacking.In this work,we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature.Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building.Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation.Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.
基金the Korea University Grant for the eightth authorCreative Materials Discovery Program through the National Research Foundation of Korea(NRF)funded by Ministry of Science and ICT(NRF-2016M3D1A1023383)+1 种基金the Brain Korea 21 PLUS Project for Center for Creative Industrial MaterialsKorea Institute for Advancement of Technology(KIAT)grant funded by the Korea Government(MOTIE)(P0002019,The Competency Development Program for Industry Specialist)。
文摘We present a new class of metastable high-entropy alloys(HEAs),triggering deformation-induced martensitic transformation(DIMT)from face-centered-cubic(FCC)to body-centered-cubic(BCC),i.e.,BCC-DIMT.Through the ab-initio calculation based on 1 st order axial interaction model and combined with the Gibbs free energy calculation,the addition of Si is considered as a critical element which enables to reduce the intrinsic stacking fault energy(ISFE)in Si_xV_((9-x))Cr_(10)Mn_5 Fe_(46)Co_(30)(x=2,4,and 7 at.%)alloy system.The ISFE decreases from-30.4 to-35.5 mJ/m^(2)as the Si content increases from 2 to 7 at.%,which well corresponds to the reduced phase stability of FCC against HCP.The BCC-DIMT occurs in all the alloys via intermediate HCP martensite,and the HCP martensite provides nucleation sites of BCC martensite.Therefore,the transformation rate enhances as the Si content increases in an earlier deformation ra nge.However,the BCC-DIMT is also affected by the phase stability of FCC against BCC,and the stability is the highest at the Si content of 7 at.%.Thus,the 7Si alloy presents the moderate transformation rate in the later deformation range.Due to the well-controlled transformation rate and consequent strain-ha rdening rate,the 7Si alloy possesses the superior combination of strength and ductility beyond 1 GPa of tensile strength at room temperature.Our results suggest that the Si addition can be a favorable candidate in various metastable HEAs for the further property improvement.
基金This study was supported by the Fundamental Research Program(No.PNK7760)of the Korea Institute of Materials Science,Brain Korea 21 PLUS project for Center for Creative Industrial Materials(F16SN25D1706)the Future Material Discovery Project of the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT of Korea(NRF-2016M3D1A1023383)+2 种基金the NRF grant funded by the Korea government(MSIP)(NRF-2021R1A2C3006662)the NRF grant funded by the Korea Government(MSIT)(No.2020R1A2C1009744)Institute for Information communications Technology Promotion(IITP)grant funded by the Korea government(MSIP)(No.2019-0-01906,Artificial Intelligence Graduate School Program(POSTECH)).
文摘The digitized format of microstructures,or digital microstructures,plays a crucial role in modern-day materials research.Unfortunately,the acquisition of digital microstructures through experimental means can be unsuccessful in delivering sufficient resolution that is necessary to capture all relevant geometric features of the microstructures.The resolution-sensitive microstructural features overlooked due to insufficient resolution may limit one’s ability to conduct a thorough microstructure characterization and material behavior analysis such as mechanical analysis based on numerical modeling.Here,a highly efficient super-resolution imaging based on deep learning is developed using a deep super-resolution residual network to super-resolved low-resolution(LR)microstructure data for microstructure characterization and finite element(FE)mechanical analysis.Microstructure characterization and FE model based mechanical analysis using the super-resolved microstructure data not only proved to be as accurate as those based on high-resolution(HR)data but also provided insights on local microstructural features such as grain boundary normal and local stress distribution,which can be only partially considered or entirely disregarded in LR data-based analysis.
基金supported by the Center for International Scientific Studies and Collaboration (CISSC)
文摘Fullerene-reinforced A1 matrix nanocomposites were fabricated by high-energy mechanical milling followed by consolidation through hot extrusion or high-pressure torsion(HPT). The results indicate that a relatively homogeneous microstructure consisting of elongated, micrometer-sized A1 grains is formed in the hot-extruded specimens. However, the microstructure is not uniform along the radius of the HPT disks, which includes coarse grains near the center of the disk and ultrafine grains in the middle and along the edge of the specimen. Microstructural evaluations of the HPT disks indicate that A1 grain refinement occurs due to the addition of fullerene, as grain size is reduced to 60 nm from 118 nm. The formation of the harmful aluminum carbide phase is not detected during the fabrication of Al/C_(60) nanocomposites. The hardness, yield stress, and ultimate tensile strength of the Al-2 vol.% C_(60) nanocomposites are about 27-160% higher than those of the monolithic A1 samples, revealing the effective strengthening of fullerene particles in A1 matrix. Moreover,mechanical properties of the Al/fullerene nanocomposites are significantly enhanced(59-272%) by utilizing HPT in comparison to hot-extruded specimens due to their much finer A1 grain structure. The reduction in the number and the size of the dimples, as well as the formation of smooth regions on the tensile fracture surface of Al/C_(60), results in their overall lower ductility compared to monolithic Al.
基金the National Research Foundation of Korea(NRF)grant(Grant No.2021R1A2C1095139)funded by the the Ministry of Science and ICT(MSIT,Korea)。
文摘In this study, the deformation behaviors and related microstructural evolutions were investigated in either monotonic or cyclic deformation modes in an interstitial metastable high-entropy alloy. These investigations aimed to reveal the mechanisms underlying the superior low-cycle fatigue(LCF) life of this alloy.A thermomechanical process was applied to induce fine-grained(FG) and coarse-grained(CG) microstructures in Fe–30Mn–10Co–10Cr–0.4C(atomic percentage) alloy. Their superior combination of strength and ductility was attributed to the appearance of deformation-induced ε-martensite and the presence of carbon. The CG alloy showed a greater volume fraction of ε-martensite than the FG alloy in the monotonic deformation mode, and vice versa in the cyclic mode. Such a disparity was interpreted in light of the back-stress effect of the relaxed γ-grain boundaries in the latter mode. Meanwhile, the γ-to-ε phase transformation under cyclic loading at low strain amplitudes(0.4%) barely led to an improved fatigue life as compared with that at higher strain amplitudes(≥ 0.55%). The high reversibility of partial dislocation motions under cyclic loading and delaying the formation of dislocation cells through the martensitic transformation could explain why the alloys investigated in this study exhibited a superior LCF life compared with high-entropy alloys reported in previous studies.
