Body-centered cubic Ti-Zr-Nb-Ta-Mo multi-principal element alloys(MPEAs),boasting a yield strength ex-ceeding one gigapascal,emerge as promising candidates for demanding structural applications.However,their limited t...Body-centered cubic Ti-Zr-Nb-Ta-Mo multi-principal element alloys(MPEAs),boasting a yield strength ex-ceeding one gigapascal,emerge as promising candidates for demanding structural applications.However,their limited tensile ductility at room temperature presents a significant challenge to their processability and large-scale implementation.This study identifies phase decomposition as a critical factor influencing the plasticity of these alloys.The microscale phase decomposition in these MPEAs during solidification,driven by miscibility gaps,manifests as dendritic structures within grains.Closer examination reveals that the MPEAs with a pronounced thermodynamic propensity for phase decomposition are also suscep-tible to analogous phenomena at the atomic level.The atomic phase decomposition is characterized by the localized aggregation of some elements across nanometric domains,culminating in the establishment of short-range orderings(SROs).It is observed that phase decomposition for these MPEAs,occurring at both microscale and atomic scale,adheres to thermodynamic principles and can be predicted using the CALPHAD approach.The impact of phase decomposition on the plasticity of MPEAs fundamentally stems from the induced heterogeneities at three distinct levels:(1)Fluctuations in mechanical properties at the micron scale;(2)Variations in the strain field at the atomic scale;(3)Bond polarization and bond index fluctuations at the electronic scale.Consequently,the key to designing high-strength and high-plasticity MPEAs lies in maximizing lattice distortion while simultaneously minimizing the adverse effects of phase decomposition on the alloy’s plasticity(grain boundary cohesion).This research not only clarifies the mechanisms underpinning the ductile-to-brittle transition in high-strength Ti-Zr-Nb-Ta-Mo MPEAs but also offers crucial guidelines for developing advanced,high-performance alloys.展开更多
Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their ...Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their excellent thermal stability and high strength.Here we fabricated the supersaturated solid solution of Cu-20 at.%Fe,a typical immiscible alloy,in bulk state by high pressure torsion,which pro-vides a great freedom over powders for studying the microstructure evolution and mechanical properties in the process of the phase decomposition in immiscible alloys.We found that in the Cu-Fe solid solu-tion,spinodal decomposition of the Fe phases took place at the initial stage of annealing through volume diffusion.This process gives rise to:(1)metastableγ-Fe particles in the Cu grains with coherent Fe/Cu interface,and(2)the more stableα-Fe phase at the grain boundaries.This process was accompanied by moving boundary reaction which first proceeded in the pattern of spinodal decomposition and then changed into classical nucleation-growth mode with the depletion of Fe atoms in Cu.The resultant Cu-Fe nanocomposites were jointly strengthened by the ultrafine Cu andα-Fe grains according to the rule of mixture,including grain boundary strengthening and the hardening of nanoscaleγ-Fe precipitates in the Cu grains.The effects of different strengthening mechanisms were scrutinized and their contributions to mechanical properties were quantitatively evaluated.This work sheds light onto the opportunity of designing and fabricating nanostructured composites via phase decomposition in immiscible systems.展开更多
Phase decomposition can effectively enhance the mechanical properties of carbide ceramics and can overcome the difficulty of enhancing the mechanical properties of single-phase multicomponent carbide ceramics.In this ...Phase decomposition can effectively enhance the mechanical properties of carbide ceramics and can overcome the difficulty of enhancing the mechanical properties of single-phase multicomponent carbide ceramics.In this work,a series of nonstoichiometric(TiZrVNb)Cx ceramics were prepared by spark plasma sintering(SPS)at different temperatures.The effects of the carbon content on the phase composition,microstructure evolution,and mechanical properties were investigated in detail.Phase decomposition occurred with decreasing carbon content.Two different solid solutions of(Ti,V)-rich and Zr-rich phases formed from the decomposition of equimolar single-phase solid solutions,namely,the Zr-poor phase and Zr-rich phase,respectively.The distribution of Nb element is relatively uniform.The semicoherent interfaces between the Zr-poor phase and the Zr-rich phase can harden and strengthen effectively under the synergistic effect of grain refinement.Ceramics with phase decomposition structures have apparent advantages compared to single-phase high-entropy carbides.This work provides an important train of thought for the microstructure tailoring and properties optimization of multi-component carbide ceramics.展开更多
TiC/Ti_(2)AlC core-shell structure reinforced Ti-based composite coating was prepared by laser cladding technology.The effect of Ti_(2)AlC content on the microstructure and mechanical behavior of the coating was studi...TiC/Ti_(2)AlC core-shell structure reinforced Ti-based composite coating was prepared by laser cladding technology.The effect of Ti_(2)AlC content on the microstructure and mechanical behavior of the coating was studied.The results showed that the reinforced phase was mainly TiC/Ti_(2)AlC MAX phase core-shell structure at 20%Ti_(2)AlC content.According to the synthesis mechanism,Ti_(2)AlC nucleated on TiC through the diffusion of Al atoms to further generate the core-shell structure.The friction and wear test results showed that the wear resistance of the coating was significantly improved under the load distribution effect of the core-shell structure.The friction coefficient decreased to 0.342,and the wear rate reached 8.19×10^(−5)mm^(3)/(N·m),which was only 47.07%of TC4 substrate.展开更多
Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnac...Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α＂ m phase which aooears as directional rods and the round precipitates. The other was the fcc α＇m phase. 〈101〉. The orientation relationship between the a phase and transitional phase α＇m was determined as （022）α＇m （fcc）//（022^-）α（fcc）, [1^-11]α＇m, （fcc）//[2^-33]α（fcc）. The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships.展开更多
It is highly desirable to enhance the long-term stability of perovskite solar cells(PSCs)so that this class of photovoltaic cells can be effectively used for the commercialization purposes.In this contribution,attempt...It is highly desirable to enhance the long-term stability of perovskite solar cells(PSCs)so that this class of photovoltaic cells can be effectively used for the commercialization purposes.In this contribution,attempts have been made to use the two-step sequential method to dope EuBr_(2)into FAMAPbI_(3)perovskite to promote the stability.It is shown that the device durability at 85℃in air with RH of 20%-40%is improved substantially,and simultaneously the champion device efficiency of 23.04%is achieved.The enhancement in stability is attributed to two points:(ⅰ)EuBr_(2)doping effectively inhibits the decomposition andα-δphase transition of perovskite under ambient environment,and(ⅱ)EuBr_(2)aggregates in the oxidized format of Eu(BrO_(3))_(3)at perovskite grain boundaries and surface,hampering humidity erosion and mitigates degradation through coordination with H_(2)O.展开更多
Several body-centered-cubic(BCC)refractory high entropy alloys(HEAs),i.e.,Hf Nb Ta Ti Zr,Nb Ta Ti Zr,Hf Nb Ti Zr and Nb Ti Zr,were annealed at intermediate temperatures for 100 h,and their microstructures and aging be...Several body-centered-cubic(BCC)refractory high entropy alloys(HEAs),i.e.,Hf Nb Ta Ti Zr,Nb Ta Ti Zr,Hf Nb Ti Zr and Nb Ti Zr,were annealed at intermediate temperatures for 100 h,and their microstructures and aging behaviors were studied in detail.All these HEAs start to decompose into multiple phases at around 500°C,but reenter the single-phase region at significantly different temperatures which were determined to be 900,1000,1100 and above 1300°C for Hf Nb Ti Zr,Nb Ti Zr,Hf Nb Ta Ti Zr and Nb Ta Ti Zr,respectively.Our analysis indicates that the onset decomposition temperature in these four HEAs is closely related to the elemental diffusion rates while the ending decomposition temperature is strongly dependent on the elemental melting points.Our findings are important not only for understanding phase stability of HEAs in general,but also for adjusting processing parameters to optimize mechanical properties of these HEAs.展开更多
To address the relatively mediocre mechanical properties of single-phase multi-component carbide ceramics,a phase transition from a single phase to multiple phases was proposed to achieve superior mechanical propertie...To address the relatively mediocre mechanical properties of single-phase multi-component carbide ceramics,a phase transition from a single phase to multiple phases was proposed to achieve superior mechanical properties.A series of(TiZrV_(x)Nb)C_(0.8) ceramics with different V contents were fabricated by spark plasma sintering(SPS).The influence of the V content on the phase composition,microstructural evolution,and mechanical properties was investigated in detail.The transition behavior from a single phase to multiple phases is discovered and discussed.The formation of the Zr-rich phase and Zr-poor phase can be attributed to the increase in lattice distortion and mixed enthalpy caused by the addition of V.A nanometer lamellar structure with a semi-coherent interface obtained via in situ decomposition is reported for the first time in multi-component carbide ceramics.The semi-coherent interfaces with high dislocation density and strain concentration effectively improve the mechanical properties,grain refinement,and multi-phase formation.The optimal comprehensive mechanical properties of the Vickers hardness(26.3 GPa),flexural strength(369 MPa),and fracture toughness(3.1 MPa·m^(1/2))were achieved for the sample with 20 mol%V.展开更多
Aluminum-based alloys play a key role in modern engineering and are widely used in construction components in aircraft, automobiles and other means of transportation due to their light weight and superior mechanical p...Aluminum-based alloys play a key role in modern engineering and are widely used in construction components in aircraft, automobiles and other means of transportation due to their light weight and superior mechanical properties. Introduction of different nano-structure features can improve the service and the physical properties of such alloys. An improvement of an Al-based alloy has been performed based on the understanding of the relationships among compositions, processing, microstructural characteristics and properties. Knowledge of the decomposition process of the microstructure during the precipitation reaction is particularly important for future technical developments. The objective of this study is to investigate the nano-scale chemical composition in the Al-Cu, Al-Li and Al-Li-Cu alloys during the early stage of the precipitation sequence and to describe whether this compositional difference correlates with variations in the observed precipitation kinetics. Investigation of the fine scale segregation effects of dilute solutes in aluminum alloys which were experienced different heat treatments by using atom probe tomography has been achieved. The results show that an Al-1.7 at.% Cu alloy requires a long ageing time of approximately 8 h at 160°C to allow the diffusion of Cu atoms into Al matrix. For the Al-8.2 at.% Li alloy, a combination of both the natural ageing condition (48 h at room temperature) and a short artificial ageing condition (5 min at 160°C) induces increasing on the number density of the Li clusters and hence increase number of precipitated particles. Applying this combination of natural ageing and short artificial ageing conditions onto the ternary Al-4 at.% Li-1.7 at.% Cu alloy induces the formation of a Cu-rich phase. Increasing the Li content in the ternary alloy up to 8 at.% and increasing the ageing time to 30 min resulted in the precipitation processes ending with δ' particles. Thus the results contribute to the understanding of Al-alloy design.展开更多
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Nos.2022A1515220040,2023A1515220021,and 2024A1515012353)the China Postdoctoral Science Foundation(No.2023M741370)+2 种基金the National Natural Sci-ence Foundation of China(No.52005217)the University Re-search Platform and Research Projects of Guangdong Education De-partment(No.2022ZDZX3003)The first-principles research is also supported by the Dongguan AIPU Technology Company Limited.
文摘Body-centered cubic Ti-Zr-Nb-Ta-Mo multi-principal element alloys(MPEAs),boasting a yield strength ex-ceeding one gigapascal,emerge as promising candidates for demanding structural applications.However,their limited tensile ductility at room temperature presents a significant challenge to their processability and large-scale implementation.This study identifies phase decomposition as a critical factor influencing the plasticity of these alloys.The microscale phase decomposition in these MPEAs during solidification,driven by miscibility gaps,manifests as dendritic structures within grains.Closer examination reveals that the MPEAs with a pronounced thermodynamic propensity for phase decomposition are also suscep-tible to analogous phenomena at the atomic level.The atomic phase decomposition is characterized by the localized aggregation of some elements across nanometric domains,culminating in the establishment of short-range orderings(SROs).It is observed that phase decomposition for these MPEAs,occurring at both microscale and atomic scale,adheres to thermodynamic principles and can be predicted using the CALPHAD approach.The impact of phase decomposition on the plasticity of MPEAs fundamentally stems from the induced heterogeneities at three distinct levels:(1)Fluctuations in mechanical properties at the micron scale;(2)Variations in the strain field at the atomic scale;(3)Bond polarization and bond index fluctuations at the electronic scale.Consequently,the key to designing high-strength and high-plasticity MPEAs lies in maximizing lattice distortion while simultaneously minimizing the adverse effects of phase decomposition on the alloy’s plasticity(grain boundary cohesion).This research not only clarifies the mechanisms underpinning the ductile-to-brittle transition in high-strength Ti-Zr-Nb-Ta-Mo MPEAs but also offers crucial guidelines for developing advanced,high-performance alloys.
基金supported by the National Natural Science Foundation of China(No.51901007)the Fundamental Research Funds for the Central Universities+1 种基金NT was financially supported by JST CREST(JPMJCR1994)JSPS(Japan Society for the Promotion of Science)KAKENHI(Nos.20H00306,22K18888)all through the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan.
文摘Extended solid solution of immiscible systems,achieved by extreme processing approaches,can be trans-formed into nanostructured composites via phase decomposition,which are drawing great research atten-tion for their excellent thermal stability and high strength.Here we fabricated the supersaturated solid solution of Cu-20 at.%Fe,a typical immiscible alloy,in bulk state by high pressure torsion,which pro-vides a great freedom over powders for studying the microstructure evolution and mechanical properties in the process of the phase decomposition in immiscible alloys.We found that in the Cu-Fe solid solu-tion,spinodal decomposition of the Fe phases took place at the initial stage of annealing through volume diffusion.This process gives rise to:(1)metastableγ-Fe particles in the Cu grains with coherent Fe/Cu interface,and(2)the more stableα-Fe phase at the grain boundaries.This process was accompanied by moving boundary reaction which first proceeded in the pattern of spinodal decomposition and then changed into classical nucleation-growth mode with the depletion of Fe atoms in Cu.The resultant Cu-Fe nanocomposites were jointly strengthened by the ultrafine Cu andα-Fe grains according to the rule of mixture,including grain boundary strengthening and the hardening of nanoscaleγ-Fe precipitates in the Cu grains.The effects of different strengthening mechanisms were scrutinized and their contributions to mechanical properties were quantitatively evaluated.This work sheds light onto the opportunity of designing and fabricating nanostructured composites via phase decomposition in immiscible systems.
基金Financial support from the National Key R&D Program of China(2021YFB3701400)the National Natural Science Foundation of China(Nos.52032002,52372060,51972081,and U22A20128)+4 种基金the National Safety Academic Foundation(No.U2130103)China Postdoctoral Science Foundation(No.2023M730839)Heilongjiang Postdoctoral Fund(No.LBH-Z22025)the National Key Laboratory of Precision Hot Processing of Metals(No.61429092300305)Heilongjiang Touyan Team Program are gratefully acknowledged.The authors thank Professor Suk-Joong L.Kang(Department of Materials Science and Engineering,Korea Advanced Institute of Science and Technology,Republic of Korea)for his assistance in editing.
文摘Phase decomposition can effectively enhance the mechanical properties of carbide ceramics and can overcome the difficulty of enhancing the mechanical properties of single-phase multicomponent carbide ceramics.In this work,a series of nonstoichiometric(TiZrVNb)Cx ceramics were prepared by spark plasma sintering(SPS)at different temperatures.The effects of the carbon content on the phase composition,microstructure evolution,and mechanical properties were investigated in detail.Phase decomposition occurred with decreasing carbon content.Two different solid solutions of(Ti,V)-rich and Zr-rich phases formed from the decomposition of equimolar single-phase solid solutions,namely,the Zr-poor phase and Zr-rich phase,respectively.The distribution of Nb element is relatively uniform.The semicoherent interfaces between the Zr-poor phase and the Zr-rich phase can harden and strengthen effectively under the synergistic effect of grain refinement.Ceramics with phase decomposition structures have apparent advantages compared to single-phase high-entropy carbides.This work provides an important train of thought for the microstructure tailoring and properties optimization of multi-component carbide ceramics.
基金Project(52365020) supported by the National Natural Science Foundation of ChinaProject([2022]06) supported by the Special Fund for Special Posts of Guizhou University,China+2 种基金Project([2024]03) supported by the Guizhou University Fund,ChinaProject(ZK[2023]78) supported by the Guizhou Provincial Basic Research Program(Natural Science),ChinaProject(BQW[2024]011) supported by the Guizhou Province Science and Technology Foundation,China。
文摘TiC/Ti_(2)AlC core-shell structure reinforced Ti-based composite coating was prepared by laser cladding technology.The effect of Ti_(2)AlC content on the microstructure and mechanical behavior of the coating was studied.The results showed that the reinforced phase was mainly TiC/Ti_(2)AlC MAX phase core-shell structure at 20%Ti_(2)AlC content.According to the synthesis mechanism,Ti_(2)AlC nucleated on TiC through the diffusion of Al atoms to further generate the core-shell structure.The friction and wear test results showed that the wear resistance of the coating was significantly improved under the load distribution effect of the core-shell structure.The friction coefficient decreased to 0.342,and the wear rate reached 8.19×10^(−5)mm^(3)/(N·m),which was only 47.07%of TC4 substrate.
文摘Furnace cooling is a slow cooling process. It is of importance to study structural evolution and its effects on the properties of alloys during the furnace cooling. Decomposition of aluminium rich α phase in a furnace cooled eutectoid Zn-Al based alloy was studied by transmission electron microscopy. Two kinds of precipitates in the α phase were detected in the FCZA22 alloy during ageing at 170℃. One was the hcp transitional α＂ m phase which aooears as directional rods and the round precipitates. The other was the fcc α＇m phase. 〈101〉. The orientation relationship between the a phase and transitional phase α＇m was determined as （022）α＇m （fcc）//（022^-）α（fcc）, [1^-11]α＇m, （fcc）//[2^-33]α（fcc）. The non-equilibrium phase decomposition of the α phase is discussed in correlation with the equilibrium phase relationships.
基金Project supported by the Fundamental Research Program of Shanxi Province,China (Grant No.20210302124228)the National Key Research and Development Program of China (Grant No.2022YFB4200203)+1 种基金the Key Project of Natural Science Foundation of Tianjin (Grant No.22JCZDJC00120)the 111 Project (Grant No.B16027)。
文摘It is highly desirable to enhance the long-term stability of perovskite solar cells(PSCs)so that this class of photovoltaic cells can be effectively used for the commercialization purposes.In this contribution,attempts have been made to use the two-step sequential method to dope EuBr_(2)into FAMAPbI_(3)perovskite to promote the stability.It is shown that the device durability at 85℃in air with RH of 20%-40%is improved substantially,and simultaneously the champion device efficiency of 23.04%is achieved.The enhancement in stability is attributed to two points:(ⅰ)EuBr_(2)doping effectively inhibits the decomposition andα-δphase transition of perovskite under ambient environment,and(ⅱ)EuBr_(2)aggregates in the oxidized format of Eu(BrO_(3))_(3)at perovskite grain boundaries and surface,hampering humidity erosion and mitigates degradation through coordination with H_(2)O.
基金supported by the National Natural Science Foundation of China(Nos.11790293,51871016,51671021,51971017,51921001)111 Project(No.B07003)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University of China(No.IRT_14R05)the financial support from the National Key Basic Research Program,China(No.2016YFB0300502)。
文摘Several body-centered-cubic(BCC)refractory high entropy alloys(HEAs),i.e.,Hf Nb Ta Ti Zr,Nb Ta Ti Zr,Hf Nb Ti Zr and Nb Ti Zr,were annealed at intermediate temperatures for 100 h,and their microstructures and aging behaviors were studied in detail.All these HEAs start to decompose into multiple phases at around 500°C,but reenter the single-phase region at significantly different temperatures which were determined to be 900,1000,1100 and above 1300°C for Hf Nb Ti Zr,Nb Ti Zr,Hf Nb Ta Ti Zr and Nb Ta Ti Zr,respectively.Our analysis indicates that the onset decomposition temperature in these four HEAs is closely related to the elemental diffusion rates while the ending decomposition temperature is strongly dependent on the elemental melting points.Our findings are important not only for understanding phase stability of HEAs in general,but also for adjusting processing parameters to optimize mechanical properties of these HEAs.
基金the National Natural Science Foundation of China (Nos. 52032002, 52372060, 51972081, and U22A20128)the National Safety Academic Foundation (No. U2130103)+4 种基金the National Key R&D Program of China (No. 2021YFB3701400)the China Postdoctoral Science Foundation (No. 2023M730839)the Heilongjiang Postdoctoral Fund (No. LBH-Z22025)the National Key Laboratory of Precision Hot Processing of Metals (No. 61429092300305)the Heilongjiang Touyan Team Program are gratefully acknowledged. The authors thank Professor Suk-Joong L. Kang (Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Republic of Korea) for his assistance in editing. The support of the thermodynamic calculations with FactSage software provided by Professor Yudong Fu (College of Material Science and Chemical Engineering, Harbin Engineering University, China) is also acknowledged.
文摘To address the relatively mediocre mechanical properties of single-phase multi-component carbide ceramics,a phase transition from a single phase to multiple phases was proposed to achieve superior mechanical properties.A series of(TiZrV_(x)Nb)C_(0.8) ceramics with different V contents were fabricated by spark plasma sintering(SPS).The influence of the V content on the phase composition,microstructural evolution,and mechanical properties was investigated in detail.The transition behavior from a single phase to multiple phases is discovered and discussed.The formation of the Zr-rich phase and Zr-poor phase can be attributed to the increase in lattice distortion and mixed enthalpy caused by the addition of V.A nanometer lamellar structure with a semi-coherent interface obtained via in situ decomposition is reported for the first time in multi-component carbide ceramics.The semi-coherent interfaces with high dislocation density and strain concentration effectively improve the mechanical properties,grain refinement,and multi-phase formation.The optimal comprehensive mechanical properties of the Vickers hardness(26.3 GPa),flexural strength(369 MPa),and fracture toughness(3.1 MPa·m^(1/2))were achieved for the sample with 20 mol%V.
文摘Aluminum-based alloys play a key role in modern engineering and are widely used in construction components in aircraft, automobiles and other means of transportation due to their light weight and superior mechanical properties. Introduction of different nano-structure features can improve the service and the physical properties of such alloys. An improvement of an Al-based alloy has been performed based on the understanding of the relationships among compositions, processing, microstructural characteristics and properties. Knowledge of the decomposition process of the microstructure during the precipitation reaction is particularly important for future technical developments. The objective of this study is to investigate the nano-scale chemical composition in the Al-Cu, Al-Li and Al-Li-Cu alloys during the early stage of the precipitation sequence and to describe whether this compositional difference correlates with variations in the observed precipitation kinetics. Investigation of the fine scale segregation effects of dilute solutes in aluminum alloys which were experienced different heat treatments by using atom probe tomography has been achieved. The results show that an Al-1.7 at.% Cu alloy requires a long ageing time of approximately 8 h at 160°C to allow the diffusion of Cu atoms into Al matrix. For the Al-8.2 at.% Li alloy, a combination of both the natural ageing condition (48 h at room temperature) and a short artificial ageing condition (5 min at 160°C) induces increasing on the number density of the Li clusters and hence increase number of precipitated particles. Applying this combination of natural ageing and short artificial ageing conditions onto the ternary Al-4 at.% Li-1.7 at.% Cu alloy induces the formation of a Cu-rich phase. Increasing the Li content in the ternary alloy up to 8 at.% and increasing the ageing time to 30 min resulted in the precipitation processes ending with δ' particles. Thus the results contribute to the understanding of Al-alloy design.
