As the speeds of trains increase,higher demands are placed on brake materials.In order to overcome the thermal degradation phenomenon of brake pads during high-speed braking,we prepared copper fiber reinforced alkali-...As the speeds of trains increase,higher demands are placed on brake materials.In order to overcome the thermal degradation phenomenon of brake pads during high-speed braking,we prepared copper fiber reinforced alkali-activated slag composite(AASC)friction materials by hot-pressing method,using slag as matrix,Na_(2)SiO_(3)·9H_(2)O as alkali excitant,copper fiber as reinforcement,and graphite as friction modifier.The results show that the AASC prepared by hot-pressing method has undergone alkali-activated reaction and has geopolymer amorphous characteristics as the conventional cast molding AASC by XRD analysis.The addition of copper fibers can improve the mechanical strength and toughness of the composites substantially,and the AASC has the highest flexural strength,compressive strength and impact toughness when the volume fraction of copper fibers reaches 25 vol%.Toughening mechanisms such as drawing,bridging and crack deflection of copper fibers in composites were analyzed by SEM morphology.Addition of appropriate amount of graphite to AASC can effectively reduce the wear rate and improve the stability of the material friction coefficient.The coefficient of friction also remains stable in the high-speed friction experiments without thermal degradation.Therefore,copper fiber reinforced AASC friction materials prepared by hot-pressing method has good mechanical and friction properties.展开更多
12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray dif...12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray diffraction （XRD）, transmission electron microscope （TEM） and energy dispersive spectroscopy （EDS）. A multiple layer interface structure, which is composed of Al/ WAl12/AlnC3/WC, is found to form by the interfacial reaction during hot-pressing. Further study shows that the AlaC3 layer forms along with a given crystal orientation of WC phase and might retard the interfacial reaction process.展开更多
Synthesis and ion transport properties of hot-pressed solid polymer electrolytes （SPEs）, （l-x） PEO： x KI, where x is the content of KI in wt%, are reported. A hot-press technique has been used for the formation o...Synthesis and ion transport properties of hot-pressed solid polymer electrolytes （SPEs）, （l-x） PEO： x KI, where x is the content of KI in wt%, are reported. A hot-press technique has been used for the formation of the polymeric membranes in place of the usual solution cast method. The composition （80 PEO：20 KI） was identified as the highest conducting polymer electrolyte on the basis of compositional dependent conductivity studies of PEO：KI films. A conductivity enhancement of more than two orders of magnitude from that of the pure PEO was achieved. Materials characterization and ion transport mechanism were explained by using various experimental techniques.展开更多
Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were...Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m(1/2) at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.展开更多
A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behav...A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.展开更多
The three-layered(W-60 vol%Cu/W-40 vol%Cu/W-20 vol%Cu)W/Cu functionally graded material(FGM)containing a Cu network structure was fabricated at different temperatures by hot-pressed sintering produced from copper-coat...The three-layered(W-60 vol%Cu/W-40 vol%Cu/W-20 vol%Cu)W/Cu functionally graded material(FGM)containing a Cu network structure was fabricated at different temperatures by hot-pressed sintering produced from copper-coated tungsten powders.The effects of various sintering temperatures on relative density,microstructure,thermal conductivity,hardness and flexural strength were investigated.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)analysis show that a Cu network extends throughout the W/Cu FGM specimens sintered at 1065℃and the graded structure can be retained perfectly,and W particles are distributed homogeneously.The low-temperature sintering densification of W/Cu FGM arises because the sintering mode of the copper-coated tungsten particles includes just sintering Cu to Cu,rather than Cu to W,Cu to Cu and W to W,as required for conventional powder particles.The relative density of W/Cu FGM sintered at 1065℃for 3 h under a load of25 MPa is 96.1%.The thermal conductivity is up to204 W·m^-1·K^-1 at normal temperature and 150 W·m^-1·K^-1at 800℃.And the Vickers hardness varies with the gradient of different layers from 3.34 to 4.05 GPa.展开更多
Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. C...Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam^(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.展开更多
Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting...Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting point of Fe.Herein,a new Fe-As alloy was obtained by mechanical alloying(MA) followed by vacuum hot-pressed sintering(VHPS).Moreover,a systematic study was carried out on the microstructural evolution,phase composition,leaching toxicity of As,and physical and mechanical properties of Fe-As alloys with varying weight fractions of As(20%,25%,30%,35%,45%,55%,65%,and 75%).The results showed that pre-alloyed metallic powders(PAMPs) have a fine grain size and specific supersaturated solid solution after MA,which could effectively improve the mechanical properties of Fe-As alloys by VHPS.A high density(> 7.350 g·cm^(-3)),low toxicity,and excellent mechanical properties could be obtained for FeAs alloys sintered via VHPS by adding an appropriate amount of As,which is more valuable than commercial Fe-As products.The Fe-25% As alloy with low toxicity and a relatively high density(7.635 g·cm^(-3)) provides an ultra-high compressive strength(1989.19 MPa),while the Fe-65% As alloy owns the maximum Vickers hardness(HVo.5 899.41).After leaching by the toxicity characteristic leaching procedure(TCLP),these alloys could still maintain good mechanical performance,and the strengthening mechanisms of Fe-As alloys before and after leaching were clarified.Changes in the grain size,micro structure,and phase distribution induced significant differences in the compressive strength and hardness.展开更多
基金Funded by the National Natural Science Foundation of China(No.51236003)the Natural Science Foundation of Gansu Province(No.1506RJZA076)。
文摘As the speeds of trains increase,higher demands are placed on brake materials.In order to overcome the thermal degradation phenomenon of brake pads during high-speed braking,we prepared copper fiber reinforced alkali-activated slag composite(AASC)friction materials by hot-pressing method,using slag as matrix,Na_(2)SiO_(3)·9H_(2)O as alkali excitant,copper fiber as reinforcement,and graphite as friction modifier.The results show that the AASC prepared by hot-pressing method has undergone alkali-activated reaction and has geopolymer amorphous characteristics as the conventional cast molding AASC by XRD analysis.The addition of copper fibers can improve the mechanical strength and toughness of the composites substantially,and the AASC has the highest flexural strength,compressive strength and impact toughness when the volume fraction of copper fibers reaches 25 vol%.Toughening mechanisms such as drawing,bridging and crack deflection of copper fibers in composites were analyzed by SEM morphology.Addition of appropriate amount of graphite to AASC can effectively reduce the wear rate and improve the stability of the material friction coefficient.The coefficient of friction also remains stable in the high-speed friction experiments without thermal degradation.Therefore,copper fiber reinforced AASC friction materials prepared by hot-pressing method has good mechanical and friction properties.
基金financially supported by the Program for Changjiang Scholars and Innovative Research Teams in University(PCSIRT)(No.IRT0713)
文摘12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray diffraction （XRD）, transmission electron microscope （TEM） and energy dispersive spectroscopy （EDS）. A multiple layer interface structure, which is composed of Al/ WAl12/AlnC3/WC, is found to form by the interfacial reaction during hot-pressing. Further study shows that the AlaC3 layer forms along with a given crystal orientation of WC phase and might retard the interfacial reaction process.
基金financially supported by DST, New Delhi through the ‘Fast Track Young Scientist Research Project’(No. SR/FTP/PS-23/2009)
文摘Synthesis and ion transport properties of hot-pressed solid polymer electrolytes （SPEs）, （l-x） PEO： x KI, where x is the content of KI in wt%, are reported. A hot-press technique has been used for the formation of the polymeric membranes in place of the usual solution cast method. The composition （80 PEO：20 KI） was identified as the highest conducting polymer electrolyte on the basis of compositional dependent conductivity studies of PEO：KI films. A conductivity enhancement of more than two orders of magnitude from that of the pure PEO was achieved. Materials characterization and ion transport mechanism were explained by using various experimental techniques.
文摘Alumina-(0 similar to 20 vol. pct) iron composites were fabricated by hot-pressing of well-mixed-alumina and iron powders at 1400 degreesC and 30 MPa for 30 min. Hot-pressed bodies with nearly theoretical density were obtained for addition up to 10 vol. pct Fe, but relative density decreased gradually with further increase in Fe addition. The materials exhibit a homogeneous dispersion of Fe. Fracture strength of the composites exhibits a maximum value of 604 MPa at 15 vol. pct Fe, which is 1.5 times that of alumina alone. Fracture toughness increases with the increase in Fe content, reaching 7.5 MPa.m(1/2) at 20 vol. pct Fe. The theoretical values of fracture toughness was calculated and compared with the experimental one. Toughening mechanisms of the composites are also discussed.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52101181).
文摘A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.
基金financially supported by the Wenzhou Public Welfare Technology Research Industry Project(No.G20140042)。
文摘The three-layered(W-60 vol%Cu/W-40 vol%Cu/W-20 vol%Cu)W/Cu functionally graded material(FGM)containing a Cu network structure was fabricated at different temperatures by hot-pressed sintering produced from copper-coated tungsten powders.The effects of various sintering temperatures on relative density,microstructure,thermal conductivity,hardness and flexural strength were investigated.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)analysis show that a Cu network extends throughout the W/Cu FGM specimens sintered at 1065℃and the graded structure can be retained perfectly,and W particles are distributed homogeneously.The low-temperature sintering densification of W/Cu FGM arises because the sintering mode of the copper-coated tungsten particles includes just sintering Cu to Cu,rather than Cu to W,Cu to Cu and W to W,as required for conventional powder particles.The relative density of W/Cu FGM sintered at 1065℃for 3 h under a load of25 MPa is 96.1%.The thermal conductivity is up to204 W·m^-1·K^-1 at normal temperature and 150 W·m^-1·K^-1at 800℃.And the Vickers hardness varies with the gradient of different layers from 3.34 to 4.05 GPa.
文摘Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam^(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.
基金financially supported by the National Natural Science Foundation of China (No.52104406)the Natural Science Foundation of Hunan Province (No.2022JJ20074)+1 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No.52121004)the National Natural Science Foundation of China for Distinguished Young Scholars (No.51825403)。
文摘Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting point of Fe.Herein,a new Fe-As alloy was obtained by mechanical alloying(MA) followed by vacuum hot-pressed sintering(VHPS).Moreover,a systematic study was carried out on the microstructural evolution,phase composition,leaching toxicity of As,and physical and mechanical properties of Fe-As alloys with varying weight fractions of As(20%,25%,30%,35%,45%,55%,65%,and 75%).The results showed that pre-alloyed metallic powders(PAMPs) have a fine grain size and specific supersaturated solid solution after MA,which could effectively improve the mechanical properties of Fe-As alloys by VHPS.A high density(> 7.350 g·cm^(-3)),low toxicity,and excellent mechanical properties could be obtained for FeAs alloys sintered via VHPS by adding an appropriate amount of As,which is more valuable than commercial Fe-As products.The Fe-25% As alloy with low toxicity and a relatively high density(7.635 g·cm^(-3)) provides an ultra-high compressive strength(1989.19 MPa),while the Fe-65% As alloy owns the maximum Vickers hardness(HVo.5 899.41).After leaching by the toxicity characteristic leaching procedure(TCLP),these alloys could still maintain good mechanical performance,and the strengthening mechanisms of Fe-As alloys before and after leaching were clarified.Changes in the grain size,micro structure,and phase distribution induced significant differences in the compressive strength and hardness.
