(38vo1% SiCp + 2vo1% A1203f)/2024 A1 composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microst...(38vo1% SiCp + 2vo1% A1203f)/2024 A1 composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microstructures and mechanical properties of the final com- posites were investigated. The results showed that the composite with 15 μm graphite powder as a forming filler had the maximum tensile strength of 506 MPa, maximum yield strength of 489 MPa, and maximum elongation of 1.2%, which decreased to 490 MPa, 430 MPa, and 0.4%, respectively, on increasing the graphite powder size from 15 to 60 μm. The composite with 60 μm graphite powder showed the highest elastic modulus, and the value decreased from 129 to 113 GPa on decreasing the graphite powder size from 60 to 15 μm. The differences between these properties are related to the different microstructures of the corresponding composites, which determine their failure modes.展开更多
Nickel-coated graphite flakes/copper(GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes(GFs) being modified by Ni–P electroless plating. The effects of the phase trans...Nickel-coated graphite flakes/copper(GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes(GFs) being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity(TC) of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20 vol%–30 vol% graphite flakes. However, when the graphite flake content was greater than 30 vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.展开更多
The magnesium matrix composites reinforced by graphite particles and Al2O3 short fibers were fabricated by squeeze-infiltration technique.The additions dispersed uniformly and no agglomeration and casting defect were ...The magnesium matrix composites reinforced by graphite particles and Al2O3 short fibers were fabricated by squeeze-infiltration technique.The additions dispersed uniformly and no agglomeration and casting defect were observed.The microstructures and wear properties of the composites with different Ce contents of 0,0.4%,0.8%and 1.0%,respectively,were investigated.Especially,the effect of Ce on the properties was discussed.The results reveal that Ce enriches around the boundaries of graphite particles and forms Al3Ce phase with Al.The addition of Ce refines the microstructures of the composites.With the increase of Ce content,the grain size becomes smaller and the wear resistance of the composite is improved.At low load,the composites have similar worn surface.At high load,the composite with 1.0%Ce has the best wear resistance due to the existence of Al3Ce phase.The Al3Ce phase improves the thermal stability of the matrix so the graphite particles can keep intact,which can still work as lubricant. At low load,the wear mechanism is abrasive wear and oxidation wear.At high load,the wear mechanism changes to delamination wear for all the composites.展开更多
Copper has good electrical conductivity but poor mechanical and wear-resistant properties.To enhance the mechanical and wear-resistant properties of the copper matrix,a strategy of in-situ generation of graphene was a...Copper has good electrical conductivity but poor mechanical and wear-resistant properties.To enhance the mechanical and wear-resistant properties of the copper matrix,a strategy of in-situ generation of graphene was adopted.Through ball-milling processes,a carbon source and submicron spherical copper were uniformly dispersed in a dendritic copper.Then,a uniform and continuous graphene network was generated in-situ in the copper matrix during the vacuum hot-pressing sintering process to improve the performance of composites.The graphene product exhibited lubrication effect and provided channels for electrons to move through the interface,improving the wear resistance and the electrical conductivity of composites.When the graphene content in the composite material was 0.100 wt.%,the friction coefficient and the wear rate were 0.36 and 6.36×10^(-6)mm^(3)·N^(-1)·m^(-1),diminished by 52%and reduced 5.11 times those of pure copper,respectively,while the electrical conductivity rose to 94.57% IACS and the hardness was enhanced by 47.8%.Therefore,this method provides a new approach for the preparation of highly conductive and wear-resistant copper matrix composite materials.展开更多
Strengthening interface bonding between boron nitride nanosheets(BNNS)and copper matrix is an essential prerequisite for exploiting a new generation of copper matrix composites(CMCs)with high strength and wear resista...Strengthening interface bonding between boron nitride nanosheets(BNNS)and copper matrix is an essential prerequisite for exploiting a new generation of copper matrix composites(CMCs)with high strength and wear resistance.Herein,BNNS/Cu composites were fabricated by the powder metallurgy route,matrix-alloying(adding 1.0 wt%Ti)strategy was adopted to improve the interfacial wettability and strengthen interface adhesion.A typical"sandwich"-like multiply interface structure involving TiN transition layers,BNNS and Cu matrix had been well constructed through the rational heat treatment(900℃ for 120 min).Additionally,nano-sized TiB whisker was in situ formed in the vicinity of the interface,it had linked the BNNS-Cu-TiN multiply interface,which played a role of"threading the needle"and significantly strengthened the multi-interfaces bonding.This specific interface structure was finely characterized,and the formation mechanism of solid-state interfacial reaction feature was proposed.The results demonstrated that the ultimate tensile strength(UTS)of BNNS/Cu-(Ti)-900℃ increased from 248 to 530 MPa(increased by 114%),and the coefficient of friction(COF)decreased from 0.51 to 0.28 than pure Cu.This work highlights the importance of interface configuration design,which contributes to the development of CMCs with prominent comprehensive properties.展开更多
Copper coating was deposited on the surface of aluminum borate whisker by an electroless plating method.This method was used to modify the interfacial property of squeeze-casting aluminum borate whisker reinforced 606...Copper coating was deposited on the surface of aluminum borate whisker by an electroless plating method.This method was used to modify the interfacial property of squeeze-casting aluminum borate whisker reinforced 6061Al matrix composite.Interface observation indicates that the spinel reaction(MgAl2O4) is hindered by the copper coating,and the difference in interfacial reaction degree affects the tensile property and aging behavior of the composite.For the composite with less spinel reaction(MgAl2O4),its peak-aging process are postponed due to less depletion of magnesium.On the fracture surface of copper-coated composite dimples and fractures of whiskers are more,but on the fracture surface of uncoated composite pull-out of whiskers are more than that on the coated one.In uncoated composite the fracture generally originates from the near-interface-region.展开更多
Graphene reinforced copper matrix composites (Gr/Cu) were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composit...Graphene reinforced copper matrix composites (Gr/Cu) were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3 wt~ Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.展开更多
The mechanical and tribological properties of Cu-based powder metallurgy (P/M) friction composites containing 10wt%-50wt% oxide-dispersion-strengthened (ODS) Cu reinforced with nano-Al2O3 were investigated. Additi...The mechanical and tribological properties of Cu-based powder metallurgy (P/M) friction composites containing 10wt%-50wt% oxide-dispersion-strengthened (ODS) Cu reinforced with nano-Al2O3 were investigated. Additionally, the friction and wear behaviors as well as the wear mechanism of the Cu-based composites were characterized by scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS) elemental mapping. The results indicated that the Cu-based friction composite containing 30wt% ODS Cu exhibited the highest hardness and shear strength. The average and instantaneous friction coefficient curves of this sample, when operated in a high-speed train at a speed of 300 km/h, were similar to those of a commercial disc brake pad produced by Knorr-Bremse AG (Germany). Additionally, the lowest linear wear loss of the obtained samples was (0.008 ± 0.001) mm per time per face, which is much lower than that of the Knorr-Bremse pad ((0.01 ± 0.001) mm). The excellent performance of the developed pad is a consequence of the formation of a dense oxide composite layer and its close combination with the pad body.展开更多
The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion ...The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion coefficient compatible with chip materials while still ensuring the reliability of the power modules.Metal matrix composites,especially copper matrix composites,containing carbon fibers,carbon nanofibers,or diamond are considered very promising as the next generation of thermalmanagement materials in power electronic packages.These composites exhibit enhanced thermal properties,as compared to pure copper,combined with lower density.This paper presents powder metallurgy and hot uniaxial pressing fabrication techniques for copper/carbon composite materials which promise to be efficient heat-dissipation materials for power electronic modules.Thermal analyses clearly indicate that interfacial treatments are required in these composites to achieve high thermal and thermomechanical properties.Control of interfaces(through a novel reinforcement surface treatment,the addition of a carbide-forming element inside the copper powders,and processing methods),when selected carefully and processed properly,will form the right chemical/mechanical bonding between copper and carbon,enhancing all of the desired thermal and thermomechanical properties while minimizing the deleterious effects.This paper outlines a variety of methods and interfacial materials that achieve these goals.展开更多
Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, w...Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.展开更多
A 2D woven graphite fibers reinforced aluminum matrix composite with 50%Grf (volume fraction) was fabricated by the squeeze-casting technology, and its microstructure and mechanical properties were investigated. The r...A 2D woven graphite fibers reinforced aluminum matrix composite with 50%Grf (volume fraction) was fabricated by the squeeze-casting technology, and its microstructure and mechanical properties were investigated. The results show that the composite is dense, the graphite fibers are distributed uniformly in the composite. TEM observation indicates the bonding between fiber and matrix is good and little interfacial reaction is found in the Grf/Al composite. This is attributed to the better stability of graphite fiber and the fabrication process minimizing the contact time between fiber with matrix at high temperatures. The 2D woven Grf/Al composite exhibites better mechanical properties with tensile strength, bending strength and elastic modulus of 366.2, 519.7 and 110.7 GPa, respectively. SEM images suggeste that the fracture is irregular and some pulled-out fibers are found, which indicats that the high strength of fiber is not degraded.展开更多
The graphite particles and Al_2O_3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique.The researches about the effects of different graphite particle sizes on the microst...The graphite particles and Al_2O_3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique.The researches about the effects of different graphite particle sizes on the microstructure and wear property of the composites were performed under the condition of constant contents of graphite particles and Al_2O_3 short fibers.The results reveal that the grain size of the composites changes less when the graphite particle size descends.Moreover,Ce enriches around the graphite particle and Al_2O_3 short fibers and forms Al_3Ce phase with A1 element.The graphite that works as lubricant decreases the wear loss.The wear resistance of the composites increases as the graphite particle size increases.At low load the composites have similar wear loss;at high load the composite with the largest graphite particle size has the best wear resistance.The wear mechanism of all the composites at low load is abrasive wear and oxidation wear;at high load,except the composites with the particle size of 240μm whose wear mechanism is still abrasive wear and oxidation wear,the wear mechanism of others changes to delamination wear.展开更多
Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work.The effect of the addition of Mg on distribution of the graphite particles has been i...Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work.The effect of the addition of Mg on distribution of the graphite particles has been investigated.Scanning electron microscopy (SEM) was used to observe the micro-morphology of Al alloy matrix composites reinforced with graphite particles.Meanwhile,the content of graphite was analyzed in the different position of casting by dissolution method and the mechanical properties of the composites were detected.The results show that the content of graphite increase with increasing Mg content;the graphite particles distribute uniformly in the particle reinforced metal matrix composites (PMMC) with 0.6 wt pct Mg;however,the agglomeration of the graphite particles is observed obviously in the matrix when Mg content is more than 1.0 wt pct.In addition,the proper Mg addition amount is beneficial to enhance the mechanical properties of the graphite particles reinforced Al alloy matrix composites and the abrasion resistance of the materials due to a reduce friction coefficient.展开更多
Cu-Al2O3 (Ag-Al2O3) nano-array composite structures were obtained by alternating current (AC) electrodeposition Cu (Ag) into the pores of anodic alumina. Their transmitted spectra and polarized properties were i...Cu-Al2O3 (Ag-Al2O3) nano-array composite structures were obtained by alternating current (AC) electrodeposition Cu (Ag) into the pores of anodic alumina. Their transmitted spectra and polarized properties were investigated in detail. Experimental results indicate that the transmittance of Cu-Al2O3 is superior to that of Ag-Al2O3 in visible and infrared wavebands, and the extinction ratio is better than that of Ag-Al2O3 in near infrared waveband.展开更多
A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers...A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide(r GO), SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2+. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.展开更多
基金funded by the National Natural Science Foundation of China (Grant No. 51174029 and No. 51374028)National High Technology Research and Development Program of China (No. 2013AA031005)Beijing Higher Education Young Elite Teacher Project (No. YETP0417)
文摘(38vo1% SiCp + 2vo1% A1203f)/2024 A1 composites were fabricated by pressure infiltration. Graphite powder was introduced as a forming filler in preform preparation, and the effects of the powder size on the microstructures and mechanical properties of the final com- posites were investigated. The results showed that the composite with 15 μm graphite powder as a forming filler had the maximum tensile strength of 506 MPa, maximum yield strength of 489 MPa, and maximum elongation of 1.2%, which decreased to 490 MPa, 430 MPa, and 0.4%, respectively, on increasing the graphite powder size from 15 to 60 μm. The composite with 60 μm graphite powder showed the highest elastic modulus, and the value decreased from 129 to 113 GPa on decreasing the graphite powder size from 60 to 15 μm. The differences between these properties are related to the different microstructures of the corresponding composites, which determine their failure modes.
基金financially supported by the National Natural Science Foundation of China (No. 51374028)Fundamental Research Funds for the Central Universities (FRF-GF-17-B37)
文摘Nickel-coated graphite flakes/copper(GN/Cu) composites were fabricated by spark plasma sintering with the surface of graphite flakes(GFs) being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity(TC) of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20 vol%–30 vol% graphite flakes. However, when the graphite flake content was greater than 30 vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.
基金Projects(20085012,20060308)supported by the Development Program of Science and Technology of Jilin Province,ChinaProject supported by"985 Project"of Jilin University,China
文摘The magnesium matrix composites reinforced by graphite particles and Al2O3 short fibers were fabricated by squeeze-infiltration technique.The additions dispersed uniformly and no agglomeration and casting defect were observed.The microstructures and wear properties of the composites with different Ce contents of 0,0.4%,0.8%and 1.0%,respectively,were investigated.Especially,the effect of Ce on the properties was discussed.The results reveal that Ce enriches around the boundaries of graphite particles and forms Al3Ce phase with Al.The addition of Ce refines the microstructures of the composites.With the increase of Ce content,the grain size becomes smaller and the wear resistance of the composite is improved.At low load,the composites have similar worn surface.At high load,the composite with 1.0%Ce has the best wear resistance due to the existence of Al3Ce phase.The Al3Ce phase improves the thermal stability of the matrix so the graphite particles can keep intact,which can still work as lubricant. At low load,the wear mechanism is abrasive wear and oxidation wear.At high load,the wear mechanism changes to delamination wear for all the composites.
基金support from the Central Government Guides Local Science and Technology Development(CN)(Grant No.[2019]4011).
文摘Copper has good electrical conductivity but poor mechanical and wear-resistant properties.To enhance the mechanical and wear-resistant properties of the copper matrix,a strategy of in-situ generation of graphene was adopted.Through ball-milling processes,a carbon source and submicron spherical copper were uniformly dispersed in a dendritic copper.Then,a uniform and continuous graphene network was generated in-situ in the copper matrix during the vacuum hot-pressing sintering process to improve the performance of composites.The graphene product exhibited lubrication effect and provided channels for electrons to move through the interface,improving the wear resistance and the electrical conductivity of composites.When the graphene content in the composite material was 0.100 wt.%,the friction coefficient and the wear rate were 0.36 and 6.36×10^(-6)mm^(3)·N^(-1)·m^(-1),diminished by 52%and reduced 5.11 times those of pure copper,respectively,while the electrical conductivity rose to 94.57% IACS and the hardness was enhanced by 47.8%.Therefore,this method provides a new approach for the preparation of highly conductive and wear-resistant copper matrix composite materials.
基金financially supported by Yunnan Fundamental Research Projects(No.202301BE070001-007)。
文摘Strengthening interface bonding between boron nitride nanosheets(BNNS)and copper matrix is an essential prerequisite for exploiting a new generation of copper matrix composites(CMCs)with high strength and wear resistance.Herein,BNNS/Cu composites were fabricated by the powder metallurgy route,matrix-alloying(adding 1.0 wt%Ti)strategy was adopted to improve the interfacial wettability and strengthen interface adhesion.A typical"sandwich"-like multiply interface structure involving TiN transition layers,BNNS and Cu matrix had been well constructed through the rational heat treatment(900℃ for 120 min).Additionally,nano-sized TiB whisker was in situ formed in the vicinity of the interface,it had linked the BNNS-Cu-TiN multiply interface,which played a role of"threading the needle"and significantly strengthened the multi-interfaces bonding.This specific interface structure was finely characterized,and the formation mechanism of solid-state interfacial reaction feature was proposed.The results demonstrated that the ultimate tensile strength(UTS)of BNNS/Cu-(Ti)-900℃ increased from 248 to 530 MPa(increased by 114%),and the coefficient of friction(COF)decreased from 0.51 to 0.28 than pure Cu.This work highlights the importance of interface configuration design,which contributes to the development of CMCs with prominent comprehensive properties.
文摘Copper coating was deposited on the surface of aluminum borate whisker by an electroless plating method.This method was used to modify the interfacial property of squeeze-casting aluminum borate whisker reinforced 6061Al matrix composite.Interface observation indicates that the spinel reaction(MgAl2O4) is hindered by the copper coating,and the difference in interfacial reaction degree affects the tensile property and aging behavior of the composite.For the composite with less spinel reaction(MgAl2O4),its peak-aging process are postponed due to less depletion of magnesium.On the fracture surface of copper-coated composite dimples and fractures of whiskers are more,but on the fracture surface of uncoated composite pull-out of whiskers are more than that on the coated one.In uncoated composite the fracture generally originates from the near-interface-region.
基金financially supported by the Natural Science Foundation of Heilongjiang Province,China(No.LC2015020)Technology Foundation for Selected Overseas Chinese Scholar,Ministry of Personnel of China(No.2015192)+1 种基金the Innovative Talent Fund ofHarbin City(No.2016RAQXJ185)Science Funds for the Young Innovative Talents of HUST(No.201604)
文摘Graphene reinforced copper matrix composites (Gr/Cu) were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3 wt~ Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.
基金financially supported by the National High Technology Research and Development Program of China (No. 2013AA031104)
文摘The mechanical and tribological properties of Cu-based powder metallurgy (P/M) friction composites containing 10wt%-50wt% oxide-dispersion-strengthened (ODS) Cu reinforced with nano-Al2O3 were investigated. Additionally, the friction and wear behaviors as well as the wear mechanism of the Cu-based composites were characterized by scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS) elemental mapping. The results indicated that the Cu-based friction composite containing 30wt% ODS Cu exhibited the highest hardness and shear strength. The average and instantaneous friction coefficient curves of this sample, when operated in a high-speed train at a speed of 300 km/h, were similar to those of a commercial disc brake pad produced by Knorr-Bremse AG (Germany). Additionally, the lowest linear wear loss of the obtained samples was (0.008 ± 0.001) mm per time per face, which is much lower than that of the Knorr-Bremse pad ((0.01 ± 0.001) mm). The excellent performance of the developed pad is a consequence of the formation of a dense oxide composite layer and its close combination with the pad body.
文摘The increase in both power and packing densities in power electronic devices has led to an increase in the market demand for effective heat-dissipating materials with a high thermal conductivity and thermal expansion coefficient compatible with chip materials while still ensuring the reliability of the power modules.Metal matrix composites,especially copper matrix composites,containing carbon fibers,carbon nanofibers,or diamond are considered very promising as the next generation of thermalmanagement materials in power electronic packages.These composites exhibit enhanced thermal properties,as compared to pure copper,combined with lower density.This paper presents powder metallurgy and hot uniaxial pressing fabrication techniques for copper/carbon composite materials which promise to be efficient heat-dissipation materials for power electronic modules.Thermal analyses clearly indicate that interfacial treatments are required in these composites to achieve high thermal and thermomechanical properties.Control of interfaces(through a novel reinforcement surface treatment,the addition of a carbide-forming element inside the copper powders,and processing methods),when selected carefully and processed properly,will form the right chemical/mechanical bonding between copper and carbon,enhancing all of the desired thermal and thermomechanical properties while minimizing the deleterious effects.This paper outlines a variety of methods and interfacial materials that achieve these goals.
基金financially supported by the National Natural Science Foundation of China (No.52171144)。
文摘Nanotubes, such as boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs), exhibit excellent mechanical properties. In this work, high-quality BNNTs were synthesized by ball milling and annealing. Subsequently, well-dispersed 3vol%BNNTs/Cu and 3vol%CNTs/Cu composites were successfully prepared using ball milling, spark plasma sintering, and followed by hot-rolling. Moreover, the mechanical properties and strengthening mechanisms of BNNTs/Cu and CNTs/Cu composites were compared and discussed in details. At 293 K,both BNNTs/Cu and CNTs/Cu composites exhibited similar ultimate tensile strength (UTS) of~404 MPa, which is approximately 170%higher than pure Cu. However, at 873 K, the UTS and yield strength of BNNTs/Cu are 27%and 29%higher than those of CNTs/Cu, respectively.This difference can be attributed to the stronger inter-walls shear resistance, higher thermomechanical stability of BNNTs, and stronger bonding at the BNNTs/Cu interface as compared to the CNTs/Cu interface. These findings provide valuable insights into the potential of BNNTs as an excellent reinforcement for metal matrix composites, particularly at high temperature.
文摘A 2D woven graphite fibers reinforced aluminum matrix composite with 50%Grf (volume fraction) was fabricated by the squeeze-casting technology, and its microstructure and mechanical properties were investigated. The results show that the composite is dense, the graphite fibers are distributed uniformly in the composite. TEM observation indicates the bonding between fiber and matrix is good and little interfacial reaction is found in the Grf/Al composite. This is attributed to the better stability of graphite fiber and the fabrication process minimizing the contact time between fiber with matrix at high temperatures. The 2D woven Grf/Al composite exhibites better mechanical properties with tensile strength, bending strength and elastic modulus of 366.2, 519.7 and 110.7 GPa, respectively. SEM images suggeste that the fracture is irregular and some pulled-out fibers are found, which indicats that the high strength of fiber is not degraded.
基金Project(2006BAE04B04-1)supported by the National Science and Technology ProgramProject(20060308)supported by theDevelopment of Science and Technology of Jilin Province ProgramProject supported by"985 Project"of Jilin University,China
文摘The graphite particles and Al_2O_3 short fibers reinforced AZ91D-0.8%Ce composites were fabricated by squeeze-infiltration technique.The researches about the effects of different graphite particle sizes on the microstructure and wear property of the composites were performed under the condition of constant contents of graphite particles and Al_2O_3 short fibers.The results reveal that the grain size of the composites changes less when the graphite particle size descends.Moreover,Ce enriches around the graphite particle and Al_2O_3 short fibers and forms Al_3Ce phase with A1 element.The graphite that works as lubricant decreases the wear loss.The wear resistance of the composites increases as the graphite particle size increases.At low load the composites have similar wear loss;at high load the composite with the largest graphite particle size has the best wear resistance.The wear mechanism of all the composites at low load is abrasive wear and oxidation wear;at high load,except the composites with the particle size of 240μm whose wear mechanism is still abrasive wear and oxidation wear,the wear mechanism of others changes to delamination wear.
基金supported financially by the National Natural Science Foundation of China (No. 50774021)the Ministry of Science and Technology of China (No.2008AA03Z512)
文摘Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work.The effect of the addition of Mg on distribution of the graphite particles has been investigated.Scanning electron microscopy (SEM) was used to observe the micro-morphology of Al alloy matrix composites reinforced with graphite particles.Meanwhile,the content of graphite was analyzed in the different position of casting by dissolution method and the mechanical properties of the composites were detected.The results show that the content of graphite increase with increasing Mg content;the graphite particles distribute uniformly in the particle reinforced metal matrix composites (PMMC) with 0.6 wt pct Mg;however,the agglomeration of the graphite particles is observed obviously in the matrix when Mg content is more than 1.0 wt pct.In addition,the proper Mg addition amount is beneficial to enhance the mechanical properties of the graphite particles reinforced Al alloy matrix composites and the abrasion resistance of the materials due to a reduce friction coefficient.
基金This work was supported by the Natural Science Foundation of Shandong Province
文摘Cu-Al2O3 (Ag-Al2O3) nano-array composite structures were obtained by alternating current (AC) electrodeposition Cu (Ag) into the pores of anodic alumina. Their transmitted spectra and polarized properties were investigated in detail. Experimental results indicate that the transmittance of Cu-Al2O3 is superior to that of Ag-Al2O3 in visible and infrared wavebands, and the extinction ratio is better than that of Ag-Al2O3 in near infrared waveband.
基金Funded by the National Natural Science Foundation of China(51572208)the 111 Project(B13035)+1 种基金the National Natural Science Foundation of Hubei Province(2014CFB257 and 2014CFB258)the Fundamental Research Funds for the Central Universities(WUT:2015-III-059)
文摘A novel chemical technique combined with unique plasma activated sintering(PAS) was utilized to prepare consolidated copper matrix composites(CMCs) by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide(r GO), SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2+. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.