To obtain the lightweight,high strength,and high damping capacity porous NiTi alloys,the microwave sintering coupled with the Mg space holder technique was employed to prepare the porous NiTi alloys.The microstructure...To obtain the lightweight,high strength,and high damping capacity porous NiTi alloys,the microwave sintering coupled with the Mg space holder technique was employed to prepare the porous NiTi alloys.The microstructure,mechanical properties,phase transformation behavior,superelasticity,and damping capacity of the porous NiTi alloys were investigated.The results show that the porous NiTi alloys are mainly composed of the B2 NiTi phase with a few B19'NiTi phase as the sintering temperature is lower than or equal to 900℃.With increasing the sintering temperature,the porosities of the porous NiTi alloys gradually decrease and the compressive strength increases first,reaching the maximum value at 900℃,and then decreases.With increasing the Mg content from 1 wt.%to 7 wt.%,the porosities of the porous NiTi alloys increase from 37.8%to 47.1%,while the compressive strength decreases from 2058 to 1146 MPa.Compared with the NH4HCO3 space holder,the phase transformation behavior of the porous NiTi alloys prepared with Mg space holder changes,and all of the compressive strength,superelasticity,shape memory effect and damping capacity are greatly improved.展开更多
The localized micro-galvanic corrosion process and the kinetic information of Mg-(7,9)Al-1Fe-x Nd alloys were investigated by in situ observation under electrochemical control and in situ atomic force microscopy(AFM)i...The localized micro-galvanic corrosion process and the kinetic information of Mg-(7,9)Al-1Fe-x Nd alloys were investigated by in situ observation under electrochemical control and in situ atomic force microscopy(AFM)in an electrolyte environment.The results revealed that the formation of the Nd-rich phase in alloys resulted in a decrease in the Volta potential difference from~400 m V(AlFe3/α-Mg)to~220 mV(Nd-rich/α-Mg),reducing the corrosion products around the cathodic phase and corrosion current density of the microscale area.The addition of Nd significantly improved the corrosion resistance,mainly due to the suppression of the micro-galvanic corrosion between the second phases and substrate.Finally,the corrosion mechanism of Mg-(7,9)Al-1Fe-x Nd alloys was discussed based on in situ observations and electrochemical results.展开更多
Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance.The reliable monitor should be high distinguishability and real-time in li...Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance.The reliable monitor should be high distinguishability and real-time in liquid environment.Herein,Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour.In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys.SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys,and their volta potentials were measured by SKPFM.According to the real-time and real-space in-situ AFM monitor,the corrosion process consisted of dissolution of anodicα-Mg phase,accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase.Then,the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.展开更多
Tungsten(W)particle-reinforced nickel(Ni)-based composites were fabricated via laser-direct energy de-position(L-DED).The influence of the W particle size on the microstructure and mechanical properties of the deposit...Tungsten(W)particle-reinforced nickel(Ni)-based composites were fabricated via laser-direct energy de-position(L-DED).The influence of the W particle size on the microstructure and mechanical properties of the deposited samples was systematically studied.The results indicate that refining the W particle size could refine theγ-Ni grains and subgrains,thin the(Ni,Cr)_(4)W interface layer,and increase the disloca-tion density of the intergranular matrix,thus improving the tensile strength and elongation of the L-DED samples.As W particle size decreased from 75 to 150μm to 6.5-12μm,the tensile strength and elonga-tion of the deposited samples increased by 150 MPa and 2.9 times to 1347.6±15.7 MPa and 17.5±0.4%,respectively.Based on the properties of the interface(Ni,Cr)_(4)W,a load-transfer efficiency factor suitable for this composite was proposed and the load-transfer strengthening formula was optimized.A quanti-tative analysis of the strengthening mechanisms was established considering load-transfer strengthening,Hall-Petch strengthening,thermal-mismatch strengthening,and solid-solution strengthening.The calcu-lated contribution of each strengthening mechanism to the yield strength and theoretical calculations were in good agreement with the experimental data.The article breaks the bottleneck of poor plasticity of W particle-reinforced Ni-based composites prepared by L-DED and provides a theoretical basis for the construction design of W particle-reinforced Ni-based composites with excellent mechanical properties.展开更多
Ultra-wideband frequency modulated continuous wave （FMCW） radar has the ability to achieve high-range resolution. Combined with the inverse synthetic aperture technique, high azimuth resolution can be realized under...Ultra-wideband frequency modulated continuous wave （FMCW） radar has the ability to achieve high-range resolution. Combined with the inverse synthetic aperture technique, high azimuth resolution can be realized under a large rotation angle. However, the range-azimuth coupling problem seriously restricts the inverse synthetic aperture radar （ISAR） imaging performance. Based on the turntable model, traditional match-filter-based, range Doppler algorithms （RDAs） and the back projection algorithm （BPA） are investigated. To eliminate the sidelobe effects of traditional algorithms, compressed sensing （CS） is preferred. Considering the block structure of a signal at high resolution, a block-sparsity adaptive matching pursuit algorithm （BSAMP） is proposed. By matching pursuit and backtracking, a signal with unknown sparsity can be recovered accurately by updating the support set iteratively. Finally, several experiments are conducted. In comparison with other algorithms, the results from processing the simulation data, some simple targets, and a complex target indicate the effectiveness and superiority of the proposed algorithm.展开更多
As nonlinear thermal devices,thermal regulators can intelligently respond to temperature and control heat flow through changes in heat transfer capacities,which allows them to reduce energy consumption without externa...As nonlinear thermal devices,thermal regulators can intelligently respond to temperature and control heat flow through changes in heat transfer capacities,which allows them to reduce energy consumption without external intervention.However,current thermal regulators generally based on high-quality crystallinestructure transitions are intrinsically rigid,which may cause structural damage and functional failure under mechanical strain;moreover,they are difficult to integrate into emerging soft electronic platforms.In this study,we develop a flexible,elastic thermal regulator based on the reversible thermally induced deformation of a liquid crystal elastomer/liquid metal(LCE/LM)composite foam.By adjusting the crosslinking densities,the LCE foam exhibits a high actuation strain of 121%with flexibility below the nematic–isotropic phase transition temperature(TNI)and hyperelasticity above TNI.The incorporation of LMresults in a high thermal resistance switching ratio of 3.8 over a wide working temperature window of 60◦C with good cycling stability.This feature originates from the synergistic effect of fragmentation and recombination of the internal LM network and lengthening and shortening of the bond line thickness.Furthermore,we fabricate a“grid window”utilizing photic-thermal integrated thermal control,achieving a superior heat supply of 13.7℃ at a light intensity of 180mW/cm^(2)and a thermal protection of 43.4℃at 1200 mW/cm^(2).The proposed method meets the mechanical softness requirements of thermal regulatormaterials with multimode intelligent temperature control.展开更多
Biomedical porous Ti-15 Mo alloys were prepared by microwave sintering using ammonium hydrogen carbonate（NH4HCO3） as the space holder agent to adjust the porosity and mechanical properties. The porous Ti-15 Mo alloy...Biomedical porous Ti-15 Mo alloys were prepared by microwave sintering using ammonium hydrogen carbonate（NH4HCO3） as the space holder agent to adjust the porosity and mechanical properties. The porous Ti-15 Mo alloys are dominated by β-Ti phase with a little α-Ti phase, and the proportion of α and β phase has no significant difference as the NH4HCO3 content increases. The porosities and the average pore sizes of the porous Ti-15 Mo alloys increase with increase of the contents of NH4HCO3, while all of the compressive strength, elastic modulus and bending strength decrease. However, the compressive strength, bending strength and the elastic modulus are higher or close to those of natural bone. The surface of the porous Ti-15 Mo alloy was further modified by hydrothermal treatment, after which Na2Ti6O13 layers with needle and flake-like clusters were formed on the outer and inner surface of the porous Ti-15 Mo alloy. The hydrothermally treated porous Ti-15 Mo alloy is completely covered by the Ca-deficient apatite layers after immersed in SBF solution for 14 d, indicating that it possesses high apatiteforming ability and bioactivity. These results demonstrate that the hydrothermally treated microwave sintered porous Ti-15 Mo alloys could be a promising candidate as the bone implant.展开更多
Long-term coherent integration can remarkably improve the ability of detection and motion parameter estimation of radar for maneuvering targets.However,the linear range migration,quadratic range migration(QRM),and Dop...Long-term coherent integration can remarkably improve the ability of detection and motion parameter estimation of radar for maneuvering targets.However,the linear range migration,quadratic range migration(QRM),and Doppler frequency migration within the coherent processing interval seriously degrade the detection and estimation performance.Therefore,an efficient and noise-resistant coherent integration method based on location rotation transform(LRT)and non-uniform fast Fourier transform(NuFFT)is proposed.QRM is corrected by the second-order keystone transform.Using the relationship between the rotation angle and Doppler frequency,a novel phase compensation function is constructed.Motion parameters can be rapidly estimated by LRT and NuFFT.Compared with several representative algorithms,the proposed method achieves a nearly ideal detection performance with low computational cost.Finally,experiments based on measured radar data are conducted to verify the proposed algorithm.展开更多
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51101085,51764041,51704167)the Aeronautical Science Foundation of China(2015ZF56027,2016ZF56020)+2 种基金the Opening Project of National Engineering Research Center for Powder Metallurgy of Titanium&Rare Metals,China(2019004)the Key Laboratory of Lightweight and High Strength Structural Materials of Jiangxi Province,China(20171BCD40003)the Jiangxi Provincial Natural Science Foundation,China(20202ACBL214011).
文摘To obtain the lightweight,high strength,and high damping capacity porous NiTi alloys,the microwave sintering coupled with the Mg space holder technique was employed to prepare the porous NiTi alloys.The microstructure,mechanical properties,phase transformation behavior,superelasticity,and damping capacity of the porous NiTi alloys were investigated.The results show that the porous NiTi alloys are mainly composed of the B2 NiTi phase with a few B19'NiTi phase as the sintering temperature is lower than or equal to 900℃.With increasing the sintering temperature,the porosities of the porous NiTi alloys gradually decrease and the compressive strength increases first,reaching the maximum value at 900℃,and then decreases.With increasing the Mg content from 1 wt.%to 7 wt.%,the porosities of the porous NiTi alloys increase from 37.8%to 47.1%,while the compressive strength decreases from 2058 to 1146 MPa.Compared with the NH4HCO3 space holder,the phase transformation behavior of the porous NiTi alloys prepared with Mg space holder changes,and all of the compressive strength,superelasticity,shape memory effect and damping capacity are greatly improved.
基金financial support from the National Natural Science Foundation of China(No.51961026)。
文摘The localized micro-galvanic corrosion process and the kinetic information of Mg-(7,9)Al-1Fe-x Nd alloys were investigated by in situ observation under electrochemical control and in situ atomic force microscopy(AFM)in an electrolyte environment.The results revealed that the formation of the Nd-rich phase in alloys resulted in a decrease in the Volta potential difference from~400 m V(AlFe3/α-Mg)to~220 mV(Nd-rich/α-Mg),reducing the corrosion products around the cathodic phase and corrosion current density of the microscale area.The addition of Nd significantly improved the corrosion resistance,mainly due to the suppression of the micro-galvanic corrosion between the second phases and substrate.Finally,the corrosion mechanism of Mg-(7,9)Al-1Fe-x Nd alloys was discussed based on in situ observations and electrochemical results.
基金support by the National Natural Science Foundation of China(51961026)the Interdisciplinary Innovation Fund of Nanchang University(Project No.2019-9166-27060003).
文摘Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance.The reliable monitor should be high distinguishability and real-time in liquid environment.Herein,Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour.In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys.SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys,and their volta potentials were measured by SKPFM.According to the real-time and real-space in-situ AFM monitor,the corrosion process consisted of dissolution of anodicα-Mg phase,accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase.Then,the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.
基金supported by the Key Projects of the National Natural Science Foundation of China(Nos.92066201 and 92266101)the Jiangxi Provincial Key R&D Programme Projects(No.20212BBE51011).
文摘Tungsten(W)particle-reinforced nickel(Ni)-based composites were fabricated via laser-direct energy de-position(L-DED).The influence of the W particle size on the microstructure and mechanical properties of the deposited samples was systematically studied.The results indicate that refining the W particle size could refine theγ-Ni grains and subgrains,thin the(Ni,Cr)_(4)W interface layer,and increase the disloca-tion density of the intergranular matrix,thus improving the tensile strength and elongation of the L-DED samples.As W particle size decreased from 75 to 150μm to 6.5-12μm,the tensile strength and elonga-tion of the deposited samples increased by 150 MPa and 2.9 times to 1347.6±15.7 MPa and 17.5±0.4%,respectively.Based on the properties of the interface(Ni,Cr)_(4)W,a load-transfer efficiency factor suitable for this composite was proposed and the load-transfer strengthening formula was optimized.A quanti-tative analysis of the strengthening mechanisms was established considering load-transfer strengthening,Hall-Petch strengthening,thermal-mismatch strengthening,and solid-solution strengthening.The calcu-lated contribution of each strengthening mechanism to the yield strength and theoretical calculations were in good agreement with the experimental data.The article breaks the bottleneck of poor plasticity of W particle-reinforced Ni-based composites prepared by L-DED and provides a theoretical basis for the construction design of W particle-reinforced Ni-based composites with excellent mechanical properties.
基金Project supported by the National Natural Science Foundation of China （No. 41301481）
文摘Ultra-wideband frequency modulated continuous wave （FMCW） radar has the ability to achieve high-range resolution. Combined with the inverse synthetic aperture technique, high azimuth resolution can be realized under a large rotation angle. However, the range-azimuth coupling problem seriously restricts the inverse synthetic aperture radar （ISAR） imaging performance. Based on the turntable model, traditional match-filter-based, range Doppler algorithms （RDAs） and the back projection algorithm （BPA） are investigated. To eliminate the sidelobe effects of traditional algorithms, compressed sensing （CS） is preferred. Considering the block structure of a signal at high resolution, a block-sparsity adaptive matching pursuit algorithm （BSAMP） is proposed. By matching pursuit and backtracking, a signal with unknown sparsity can be recovered accurately by updating the support set iteratively. Finally, several experiments are conducted. In comparison with other algorithms, the results from processing the simulation data, some simple targets, and a complex target indicate the effectiveness and superiority of the proposed algorithm.
基金National Key R&D Program of China,Grant/Award Number:2022YFB3805702National Natural Science Foundation of China,Grant/Award Numbers:52173078,52130303,51973158,51803151,51973152,52303101,52327802+1 种基金Science Foundation for Distinguished Young Scholars in Tianjin,Grant/Award Number:19JCJQJC61700Young Elite Scientists Sponsorship Program by CAST,Grant/Award Number:2022QNRC001。
文摘As nonlinear thermal devices,thermal regulators can intelligently respond to temperature and control heat flow through changes in heat transfer capacities,which allows them to reduce energy consumption without external intervention.However,current thermal regulators generally based on high-quality crystallinestructure transitions are intrinsically rigid,which may cause structural damage and functional failure under mechanical strain;moreover,they are difficult to integrate into emerging soft electronic platforms.In this study,we develop a flexible,elastic thermal regulator based on the reversible thermally induced deformation of a liquid crystal elastomer/liquid metal(LCE/LM)composite foam.By adjusting the crosslinking densities,the LCE foam exhibits a high actuation strain of 121%with flexibility below the nematic–isotropic phase transition temperature(TNI)and hyperelasticity above TNI.The incorporation of LMresults in a high thermal resistance switching ratio of 3.8 over a wide working temperature window of 60◦C with good cycling stability.This feature originates from the synergistic effect of fragmentation and recombination of the internal LM network and lengthening and shortening of the bond line thickness.Furthermore,we fabricate a“grid window”utilizing photic-thermal integrated thermal control,achieving a superior heat supply of 13.7℃ at a light intensity of 180mW/cm^(2)and a thermal protection of 43.4℃at 1200 mW/cm^(2).The proposed method meets the mechanical softness requirements of thermal regulatormaterials with multimode intelligent temperature control.
基金supported by the National Natural Science Foundation of China (51101085)the Aeronautical Science Foundation of China (2015ZF56027)+2 种基金the Natural Science Foundation of Jiangxi Province (2016BAB206109)the Science and Technology Support Plan Project of Jiangxi Province (20151BBG70039)the Science and Technology Project of Jiangxi Province Education Department (GJJ150721)
文摘Biomedical porous Ti-15 Mo alloys were prepared by microwave sintering using ammonium hydrogen carbonate（NH4HCO3） as the space holder agent to adjust the porosity and mechanical properties. The porous Ti-15 Mo alloys are dominated by β-Ti phase with a little α-Ti phase, and the proportion of α and β phase has no significant difference as the NH4HCO3 content increases. The porosities and the average pore sizes of the porous Ti-15 Mo alloys increase with increase of the contents of NH4HCO3, while all of the compressive strength, elastic modulus and bending strength decrease. However, the compressive strength, bending strength and the elastic modulus are higher or close to those of natural bone. The surface of the porous Ti-15 Mo alloy was further modified by hydrothermal treatment, after which Na2Ti6O13 layers with needle and flake-like clusters were formed on the outer and inner surface of the porous Ti-15 Mo alloy. The hydrothermally treated porous Ti-15 Mo alloy is completely covered by the Ca-deficient apatite layers after immersed in SBF solution for 14 d, indicating that it possesses high apatiteforming ability and bioactivity. These results demonstrate that the hydrothermally treated microwave sintered porous Ti-15 Mo alloys could be a promising candidate as the bone implant.
基金the National Natural Science Foundation of China(No.61501513)。
文摘Long-term coherent integration can remarkably improve the ability of detection and motion parameter estimation of radar for maneuvering targets.However,the linear range migration,quadratic range migration(QRM),and Doppler frequency migration within the coherent processing interval seriously degrade the detection and estimation performance.Therefore,an efficient and noise-resistant coherent integration method based on location rotation transform(LRT)and non-uniform fast Fourier transform(NuFFT)is proposed.QRM is corrected by the second-order keystone transform.Using the relationship between the rotation angle and Doppler frequency,a novel phase compensation function is constructed.Motion parameters can be rapidly estimated by LRT and NuFFT.Compared with several representative algorithms,the proposed method achieves a nearly ideal detection performance with low computational cost.Finally,experiments based on measured radar data are conducted to verify the proposed algorithm.
