The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excell...The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excellent comprehensive performance,the evolution of texture characterization during fabrication process and subsequent effect of texture on mechanical properties are vital controlling factors.In this investigation,three experimental Mg-3Al series alloys were hot rolled and annealed to sheets with 1 mm thickness.The microstructure evolution during rolling and annealing process was investigated.Furthermore,the influence of texture on tensile properties along different tensile directions was also studied.The results show that weakened basal texture and refined grains were achieved with the co-addition of Ca and RE element.However,strengthening of mechanical properties wasn't obtained.During hot rolling process,microstructure was refined,second phase particles broken,and basal texture was increased.While basal texture was weakened during annealing process.Recrystallization behavior influenced by formation of second phase was dominated to attenuate basal texture.Tensile deformation behavior was controlled by basal slip and followed Schmid factor criterion.Moreover,the weakened basal texture and activation of non-basal slips during hot rolling process can contribute to diminish the anisotropy of tensile properties.展开更多
The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based...The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based on the low-cost alloy composition design,the corro-sion behavior of commercial Mg-3Al-1Zn(AZ31)alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy,hydrogen evolution,electrochemical measurements,and corrosion morphology analysis.Results revealed that the potential differ-ence of Al_(2)Ca/α-Mg and Mg_(2)Sn/α-Mg was(230±19)mV and(80±6)mV,respectively,much lower than that of Al_(8)Mn_(5)/α-Mg(430±31)mV in AZ31 alloy,which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance,followed by AZ31-0.2Ca,while AZ31 al-loy exhibited the worst corrosion resistance.Moreover,Sn dissolved into matrix obviously increased the potential ofα-Mg and participated in the formation of dense SnO_(2) film at the interface of matrix,while Ca element was enriched in the corrosion product layer,resulting in the cor-rosion product layer of AZ31-0.2Ca/Sn alloys more compact,stable,and protective than AZ31 alloy.Therefore,AZ31 alloy bearing 0.2wt%Ca or Sn element exhibited excellent balanced properties,which is potential to be applied in commercial more comprehensively.展开更多
Unmanned aerial vehicles(UAVs) are increasingly considered in safe autonomous navigation systems to explore unknown environments where UAVs are equipped with multiple sensors to perceive the surroundings. However, how...Unmanned aerial vehicles(UAVs) are increasingly considered in safe autonomous navigation systems to explore unknown environments where UAVs are equipped with multiple sensors to perceive the surroundings. However, how to achieve UAVenabled data dissemination and also ensure safe navigation synchronously is a new challenge. In this paper, our goal is minimizing the whole weighted sum of the UAV’s task completion time while satisfying the data transmission task requirement and the UAV’s feasible flight region constraints. However, it is unable to be solved via standard optimization methods mainly on account of lacking a tractable and accurate system model in practice. To overcome this tough issue,we propose a new solution approach by utilizing the most advanced dueling double deep Q network(dueling DDQN) with multi-step learning. Specifically, to improve the algorithm, the extra labels are added to the primitive states. Simulation results indicate the validity and performance superiority of the proposed algorithm under different data thresholds compared with two other benchmarks.展开更多
Porous Titanium scaffolds have attracted widespread attention as bone implants for avoiding the stress shielding effect and promoting bone-in-growth.In this study,multi-morphology graded scaffolds hy-bridized by Primi...Porous Titanium scaffolds have attracted widespread attention as bone implants for avoiding the stress shielding effect and promoting bone-in-growth.In this study,multi-morphology graded scaffolds hy-bridized by Primitive and Gyroid structures with porosity of 50,60,and 70%were designed(denoted as PG50,PG60,and PG70,respectively)and fabricated by selective laser melting.The simulation results showed that the maximum von-Mises stress of hybridized scaffolds increased from 504.22 to 884.24 MPa with porosity.The permeability and average pore size of multi-morphology PG50,PG60,and PG70 were in the range of 3.58×10^(-9)-5.50×10^(-9) m^(2) and 568.1-758.4μm,respectively.The microstructure of multi-morphology graded scaffolds consisted of a fully martensiticα′phase.Tested permeabilities of PG50 and PG60 were 3.27×10^(-9) and 4.35×10^(-9) m^(2),respectively,which were within the range of human bone(0.01-12.1×10^(-9) m^(2)).Elastic modulus and compressive yield strength of PG50 and PG60 ranged within 5.93^(-9).86 and 180.06-257.08 MPa,respectively.Therein,the PG50 not only exhibited a similar elastic modulus compared to human cortical bone(10.1 GPa)but also had higher strength(257.08 vs 131 MPa).The results of in vitro biocompatibility assay showed that PG50 and PG60 have better cyto-compatibility than mono-morphology scaffolds with the same porosity.Taken together,PG50 is promising to be used for the restoration of bone defects due to its excellent mechanical properties,appropriate per-meability,and good cytocompatibility.展开更多
The variation of texture characteristics and activation of deformation mechanism in magnesium alloys can be achieved by addition of RE and Ca elements and subsequently affect the microstructure evolution during deform...The variation of texture characteristics and activation of deformation mechanism in magnesium alloys can be achieved by addition of RE and Ca elements and subsequently affect the microstructure evolution during deformation process.In this manuscript,the effects of loading direction and strain rate on mechanical properties,microstructural characteristics,texture evolution and deformation mechanism in TRC-ZA21 magnesium alloy sheet were investigated.Moreover,orientation dependence and strain rate sensitivity of deformation mechanism were also discussed.The results showed that evident difference in mechanical properties in TRC-ZA21 alloy exhibited by the changes in loading direction and strain rate.The variations in grain orientation and basal texture characteristic were attributed to the grain rotation behavior during the plastic deformation,dominated by deformation mechanism.Basal slip,extension twinning and prismatic slip played different contributions to plastic deformation behavior and presented orientation dependence and strain rate sensitivity.The activities of prismatic slip and extension twinning both enhance with increasing strain rate.The phenomenon of weakened effect of twinning and promoted role of prismatic slip was presented to coordinate strain compatibility during plastic deformation.展开更多
Lithium niobate(LiNbO_(3),LN)crystal is a multi-functional material with favorable piezoelectric,nonlinear optical and electro-optic properties.In this study,the electromechanical properties of the radial extensional(...Lithium niobate(LiNbO_(3),LN)crystal is a multi-functional material with favorable piezoelectric,nonlinear optical and electro-optic properties.In this study,the electromechanical properties of the radial extensional(RE)and the thickness extensional(TE)modes of the congruent LN are studied and the temperature dependent behaviors are revealed.The RE mode electromechanical coupling factors(kp)for the Y-and Z-oriented discs are calculated and found to be 3.8%and 24.7%,respectively,which are nearly the same as the experimental results of 3.8%and 25.2%,respectively.The maximum RE and thickness shear(TS)modes electromechanical coupling factors are obtained to be 47.6%and 68.5%for the Yx/25and Yx/167crystal cuts,respectively.The LN crystal possesses good temperature stability of the electromechanical coupling factors(RE and TE modes)from 20℃ to 500℃,where the variations of kp and kt for the Y-oriented discs are<8.0%and<1.8%,respectively.展开更多
The yttrium calcium oxyborate crystal(YCa_(4)O(BO_(3))_(3),YCOB)has been actively studied for hightemperature piezoelectric sensing applications.In this work,the stability of electric properties of YCOB crystal anneal...The yttrium calcium oxyborate crystal(YCa_(4)O(BO_(3))_(3),YCOB)has been actively studied for hightemperature piezoelectric sensing applications.In this work,the stability of electric properties of YCOB crystal annealed in critical conditions(high-temperatures of 900-1100℃ with a low oxygen partial pressure of 4×10^(-6) atm for 24 h)was investigated and the recovery mechanism for the electrical resisitivity,dielectric permittivity and dielectric loss were studied,taking advantage of the X-ray photoelectron spectra and the first principle calculations.The electrical resistivity of the annealed YCOB crystal was slightly decreased when compared to the pristine counterpart,being(2-5)×10^(7) Ω·cm at 850C.The dielectric permittivity and dielectric loss were found to increase after annealing,showing recoverable behaviours after thermal treatment above 650℃ in air.The calculated vacancy formation energy indicates that the oxygen vacancy is the dominant defects in YCOB.The formation of oxygen vacancy weakens the chemical bonding strength between B(Ca or Y)and O atoms,introduces extra donor levels in the band gap,which excites the electrons to conduction band more easily thus enhances the electrical conductivity and dielectric loss.The recovered electrical properties are believed to be associated with the reduced vacancy defects at elevated temperatures in air.展开更多
基金The authors would like to thank the financial support of Fundamental Research Funds for the Central Universities(No.2302019FRF-IC-19-018)Aviation Science Foundation Project(No.20181174001).
文摘The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excellent comprehensive performance,the evolution of texture characterization during fabrication process and subsequent effect of texture on mechanical properties are vital controlling factors.In this investigation,three experimental Mg-3Al series alloys were hot rolled and annealed to sheets with 1 mm thickness.The microstructure evolution during rolling and annealing process was investigated.Furthermore,the influence of texture on tensile properties along different tensile directions was also studied.The results show that weakened basal texture and refined grains were achieved with the co-addition of Ca and RE element.However,strengthening of mechanical properties wasn't obtained.During hot rolling process,microstructure was refined,second phase particles broken,and basal texture was increased.While basal texture was weakened during annealing process.Recrystallization behavior influenced by formation of second phase was dominated to attenuate basal texture.Tensile deformation behavior was controlled by basal slip and followed Schmid factor criterion.Moreover,the weakened basal texture and activation of non-basal slips during hot rolling process can contribute to diminish the anisotropy of tensile properties.
基金This work is financially supported by the Fundamental Research Funds for the Central Universities,China(Nos.2302017FRF-IC-17-001,2302018FRF-IC-18-004,232019 FRF-IC-19-018,and 2302020FRF-IC-20-10)the China Postdoctoral Science Foundation(No.2021M700378).
文摘The limited wide applicability of commercial Mg alloys is mainly attributed to the poor corrosion resistance.Addition of alloying elements is the simplest and effective method to improve the corrosion properties.Based on the low-cost alloy composition design,the corro-sion behavior of commercial Mg-3Al-1Zn(AZ31)alloy bearing minor Ca or Sn element was characterized by scanning Kelvin probe force microscopy,hydrogen evolution,electrochemical measurements,and corrosion morphology analysis.Results revealed that the potential differ-ence of Al_(2)Ca/α-Mg and Mg_(2)Sn/α-Mg was(230±19)mV and(80±6)mV,respectively,much lower than that of Al_(8)Mn_(5)/α-Mg(430±31)mV in AZ31 alloy,which illustrated that AZ31-0.2Sn alloy performed the best corrosion resistance,followed by AZ31-0.2Ca,while AZ31 al-loy exhibited the worst corrosion resistance.Moreover,Sn dissolved into matrix obviously increased the potential ofα-Mg and participated in the formation of dense SnO_(2) film at the interface of matrix,while Ca element was enriched in the corrosion product layer,resulting in the cor-rosion product layer of AZ31-0.2Ca/Sn alloys more compact,stable,and protective than AZ31 alloy.Therefore,AZ31 alloy bearing 0.2wt%Ca or Sn element exhibited excellent balanced properties,which is potential to be applied in commercial more comprehensively.
基金supported by the National Natural Science Foundation of China (No. 61931011)。
文摘Unmanned aerial vehicles(UAVs) are increasingly considered in safe autonomous navigation systems to explore unknown environments where UAVs are equipped with multiple sensors to perceive the surroundings. However, how to achieve UAVenabled data dissemination and also ensure safe navigation synchronously is a new challenge. In this paper, our goal is minimizing the whole weighted sum of the UAV’s task completion time while satisfying the data transmission task requirement and the UAV’s feasible flight region constraints. However, it is unable to be solved via standard optimization methods mainly on account of lacking a tractable and accurate system model in practice. To overcome this tough issue,we propose a new solution approach by utilizing the most advanced dueling double deep Q network(dueling DDQN) with multi-step learning. Specifically, to improve the algorithm, the extra labels are added to the primitive states. Simulation results indicate the validity and performance superiority of the proposed algorithm under different data thresholds compared with two other benchmarks.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.51922004 and 51874037)the State Key Lab of Advanced Metals and Materials,University of Sci-ence and Technology Beijing(Nos.2020Z-04,2021Z-03,and 2022Z-12)+5 种基金the Fundamental Research Funds for the Central Universi-ties(Nos.FRF-TP-19005C1Z and 06500236)the Interdisciplinary Research Project for Young Teachers of USTB(Fundamental Re-search Funds for the Central Universities,No.FRF-IDRY-20-023)the Postdoctor Research Foundation of Shunde Graduate School of University of Science and Technology Beijing(No.2022BH001)the China Postdoctoral Science Foundation(No.2021M700377)the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515110548)the State Key Laboratory of Powder Metallurgy,Central South University and the Beijing Natural Science Founda-tion(No.2212035)。
文摘Porous Titanium scaffolds have attracted widespread attention as bone implants for avoiding the stress shielding effect and promoting bone-in-growth.In this study,multi-morphology graded scaffolds hy-bridized by Primitive and Gyroid structures with porosity of 50,60,and 70%were designed(denoted as PG50,PG60,and PG70,respectively)and fabricated by selective laser melting.The simulation results showed that the maximum von-Mises stress of hybridized scaffolds increased from 504.22 to 884.24 MPa with porosity.The permeability and average pore size of multi-morphology PG50,PG60,and PG70 were in the range of 3.58×10^(-9)-5.50×10^(-9) m^(2) and 568.1-758.4μm,respectively.The microstructure of multi-morphology graded scaffolds consisted of a fully martensiticα′phase.Tested permeabilities of PG50 and PG60 were 3.27×10^(-9) and 4.35×10^(-9) m^(2),respectively,which were within the range of human bone(0.01-12.1×10^(-9) m^(2)).Elastic modulus and compressive yield strength of PG50 and PG60 ranged within 5.93^(-9).86 and 180.06-257.08 MPa,respectively.Therein,the PG50 not only exhibited a similar elastic modulus compared to human cortical bone(10.1 GPa)but also had higher strength(257.08 vs 131 MPa).The results of in vitro biocompatibility assay showed that PG50 and PG60 have better cyto-compatibility than mono-morphology scaffolds with the same porosity.Taken together,PG50 is promising to be used for the restoration of bone defects due to its excellent mechanical properties,appropriate per-meability,and good cytocompatibility.
基金supported by the China Postdoctoral Science Foundation(No.2021M700378)the Fundamental Research Funds for the Central Universities(No.2302020FRF-IC-20-10).
文摘The variation of texture characteristics and activation of deformation mechanism in magnesium alloys can be achieved by addition of RE and Ca elements and subsequently affect the microstructure evolution during deformation process.In this manuscript,the effects of loading direction and strain rate on mechanical properties,microstructural characteristics,texture evolution and deformation mechanism in TRC-ZA21 magnesium alloy sheet were investigated.Moreover,orientation dependence and strain rate sensitivity of deformation mechanism were also discussed.The results showed that evident difference in mechanical properties in TRC-ZA21 alloy exhibited by the changes in loading direction and strain rate.The variations in grain orientation and basal texture characteristic were attributed to the grain rotation behavior during the plastic deformation,dominated by deformation mechanism.Basal slip,extension twinning and prismatic slip played different contributions to plastic deformation behavior and presented orientation dependence and strain rate sensitivity.The activities of prismatic slip and extension twinning both enhance with increasing strain rate.The phenomenon of weakened effect of twinning and promoted role of prismatic slip was presented to coordinate strain compatibility during plastic deformation.
基金the Primary Research&Development Plan of Shandong Province(2017CXGC0413)the National Natural Science Foundation of China(Grant No.51872165).
文摘Lithium niobate(LiNbO_(3),LN)crystal is a multi-functional material with favorable piezoelectric,nonlinear optical and electro-optic properties.In this study,the electromechanical properties of the radial extensional(RE)and the thickness extensional(TE)modes of the congruent LN are studied and the temperature dependent behaviors are revealed.The RE mode electromechanical coupling factors(kp)for the Y-and Z-oriented discs are calculated and found to be 3.8%and 24.7%,respectively,which are nearly the same as the experimental results of 3.8%and 25.2%,respectively.The maximum RE and thickness shear(TS)modes electromechanical coupling factors are obtained to be 47.6%and 68.5%for the Yx/25and Yx/167crystal cuts,respectively.The LN crystal possesses good temperature stability of the electromechanical coupling factors(RE and TE modes)from 20℃ to 500℃,where the variations of kp and kt for the Y-oriented discs are<8.0%and<1.8%,respectively.
基金financially supported by the Primary Research&Development Plan of Shandong Province(2017CXGC0413)the National Natural Science Foundation of China(51872165).
文摘The yttrium calcium oxyborate crystal(YCa_(4)O(BO_(3))_(3),YCOB)has been actively studied for hightemperature piezoelectric sensing applications.In this work,the stability of electric properties of YCOB crystal annealed in critical conditions(high-temperatures of 900-1100℃ with a low oxygen partial pressure of 4×10^(-6) atm for 24 h)was investigated and the recovery mechanism for the electrical resisitivity,dielectric permittivity and dielectric loss were studied,taking advantage of the X-ray photoelectron spectra and the first principle calculations.The electrical resistivity of the annealed YCOB crystal was slightly decreased when compared to the pristine counterpart,being(2-5)×10^(7) Ω·cm at 850C.The dielectric permittivity and dielectric loss were found to increase after annealing,showing recoverable behaviours after thermal treatment above 650℃ in air.The calculated vacancy formation energy indicates that the oxygen vacancy is the dominant defects in YCOB.The formation of oxygen vacancy weakens the chemical bonding strength between B(Ca or Y)and O atoms,introduces extra donor levels in the band gap,which excites the electrons to conduction band more easily thus enhances the electrical conductivity and dielectric loss.The recovered electrical properties are believed to be associated with the reduced vacancy defects at elevated temperatures in air.