Recent Advances in Interface Modification of Cu/graphite Composites and Layered Ternary Carbides of Modified Layer Candidate

We review the fundamental properties and significant issues related to Cu/graphite composites.In particular,recent research on the interfacial modification of Cu/graphite composites is addressed,including the metal-modified layer,carbide-modified layer,and combined modified layer.Additionally,we propose the use of ternary layered carbide as an interface modification layer for Cu/graphite composites.

Microstructure and properties of Cu matrix composites reinforced with surface-modified Kovar particles

The thermal conductivity of Cu/Kovar composites was improved by suppressing element diffusion at the interfaces through the formation of FeWO_(4)coating on the Kovar particles via vacuum deposition.Cu matrix composites reinforced with unmodified(Cu/Kovar)and modified Kovar(Cu/Kovar@)particles were prepared by hot pressing.The results demonstrate that the interfaces of Cu/FeWO_(4)and FeWO_(4)/Kovar in the Cu/Kovar@composites exhibit strong bonding,and no secondary phase is generated.The presence of FeWO_(4)impedes interfacial diffusion within the composite,resulting in an increase in grain size and a decrease in dislocation density.After surface modification of the Kovar particle,the thermal conductivity of Cu/Kovar@composite is increased by 110%from 40.6 to 85.6 W·m^(-1)·K^(-1).Moreover,the thermal expansion coefficient of the Cu/Kovar@composite is 9.8×10^(-6)K^(-1),meeting the electronic packaging requirements.

Morphology and Frictional Characteristics Under Electrical Currents of Al_2O_3/Cu Composites Prepared by Internal Oxidation

Two Al2O3/Cu composites containing 0.24 wt.% Al2O3 and 0.60 wt.% Al2O3 separately are prepared by internal oxidation. Effects of sliding speed and pressure on the frictional characteristics of the composites and copper against brass are investigated and compared. The changes in morphology of the sliding surface and subsurface are examined with scanning electron microscope （SEM） and energy dispersive X-ray spectrum （EDS）. The results show that the wear resistance of the Al2O3/Cu composites is superior to that of copper under the same conditions, Under a given electrical current, the wear rate of Al2O3/Cu composites decreases as the Al2O3-content increases, However, the wear rates of the Al2O3/Cu composites and copper increase as the sliding speed and pressure increase under dry sliding condition. The main wear mechanisms for Al2O3/Cu composites are of abrasion and adhesion; for copper, it is adhesion, although wear by oxidation and electrical erosion can also be observed as the speed and pressure rise.

Effect of electrical current on tribological property of Cu matrix composite reinforced by carbon nanotubes

Cu matrix composite reinforced with 10%（volume fraction） carbon nanotubes（CNTs/Cu） and pure Cu bulk were prepared by powder metallurgy techniques under the same consolidation processing condition.The effect of electrical current on tribological property of the materials was investigated by using a pin-on-disk friction and wear tester.The results show that the friction coefficient and wear rate of CNTs/Cu composite as well as those of pure Cu bulk increase with increasing the electrical current without exception,and the effect of electrical current is more obvious on tribological property of pure Cu bulk than on that of CNTs/Cu composite;the dominant wear mechanisms are arc erosion wear and plastic flow deformation,respectively;CNTs can improve tribological property of Cu matrix composites with electrical current.

Properties and microstructure of Cu/diamond composites prepared by spark plasma sintering method

Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond were successfully prepared by spark plasma sintering（SPS） method. The sintering temperatures and volume fractions（50%, 60% and 70%） of diamond were changed to investigate their effects on the relative density, homogeneity of the microstructure and thermal conductivity of the composites. The results show that the relative density, homogeneity of the microstructure and thermal conductivity of the composites increase with decreasing the diamond volume fraction; the relative density and thermal conductivity of the composites increase with increasing the sintering temperature. The thermal conductivity of the composites is a result of the combined effect of the volume fraction of diamond, the homogeneity and relative density of the composites.

Microstructural development and its effects on mechanical properties of Al/Cu laminated composite

The microstructural development and its effect on the mechanical properties of Al/Cu laminated composite produced by asymmetrical roll bonding and annealing were studied. The composite characterizations were conducted by transmission electron microscope（TEM）, scanning electron microscope（SEM）, peeling tests and tensile tests. It is found that the ultra-fine grained laminated composites with tight bonding interface are prepared by the roll bonding technique. The annealing prompts the atomic diffusion in the interface between dissimilar matrixes, and even causes the formation of intermetallic compounds. The interfacial bonding strength increases to the maximum value owing to the interfacial solution strengthening at 300 °C annealing, but sharply decreases by the damage effect of intermetallic compounds at elevated temperatures. The composites obtain high tensile strength due to the Al crystallization grains and Cu twins at 300 °C. At 350 °C annealing, however, the composites get high elongation by the interfacial interlayer with submicron thickness.

Effects of rolling and annealing on microstructures and properties of Cu/Invar electronic packaging composites prepared by powder metallurgy

The Cu/Invar composites of 40% Cu were prepared by powder metallurgy, and the composites were rolled with 70% reduction and subsequently annealed at 750 ℃. Phases, microstructures and properties of the composites were then studied. After that, the amount of a-Fe（Ni,Co） in the composites is reduced, because a-Fe（Ni,Co） partly transfers into y-Fe（Ni,Co） through the diffusion of the Ni atoms into a-Fe（Ni,Co） from Cu. When the rolling reduction is less than 40%, the deformation of Cu takes place, resulting in the movement of the Invar particles and the seaming of the pores. When the rolling reduction is in the range from 40% to 60%, the deformations of Invar and Cu occur simultaneously to form a streamline structure. After rolling till 70% and subsequent annealing, the Cu/Invar composites have fine comprehensive properties with a relative density of 98.6%, a tensile strength of 360 MPa, an elongation rate of 50%, a thermal conductivity of 25.42 W/（m.K） （as-tested） and a CTE of 10.79× 10-6/K （20-100 ℃）.

Preparation of nanosized W/Cu composite powder by sol-gel technique

Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.

Microstructure and mechanical properties of Al/Cu/Mg laminated composite sheets produced by the ARB proces

In the present study, an Al/Cu/Mg multi-layered composite was produced by accumulative roll bonding(ARB) through seven passes, and its microstructure and mechanical properties were evaluated. The microstructure investigations show that plastic instability occurred in both the copper and magnesium reinforcements in the primary sandwich. In addition, a composite with a perfectly uniform distribution of copper and magnesium reinforcing layers was produced during the last pass. By increasing the number of ARB cycles, the microhardness of the layers including aluminum, copper, and magnesium was significantly increased. The ultimate tensile strength of the sandwich was enhanced continually and reached a maximum value of 355.5 MPa. This strength value was about 3.2, 2, and 2.1 times higher than the initial strength values for the aluminum, copper, and magnesium sheets, respectively. Investigation of tensile fracture surfaces during the ARB process indicated that the fracture mechanism changed to shear ductile at the seventh pass.

Mechanical properties of Cu based composites reinforced by carbon nanotubes

Cu based composites reinforced by 0%～25% (volume fraction) carbon nanotubes were prepared.The fracture behaviors and the rolling properties of the composites and the effects of the volume fraction of the carbon nanotubes were studied.The experimental results show that the fracture toughness of the composites is related to the pulling out and bridging of the carbon nanotubes in the fracture process.With the volume fraction of the carbon nanotubes increasing, the Vicker’s hardness and the compactness of the composites increase first and then decrease. The peaks of the hardness and the compactness occur at 12%～15% of volume fraction of carbon nanotubes.Some proper ratio of rolling reduction benefits to the comprehensive mechanical properties of the composites.

Effects of intermediate Ni layer on mechanical properties of Al–Cu layered composites fabricated through cold roll bonding

Layered composites have attracted considerable interest in the recent literature on metal composites. Their mechanical properties depend on the quality of the bonding provided by the intermediate layers. In this study, we analyzed the mechanical properties and bond strengths provided by the nickel layer with respect to its thickness and nature(either powder or coating). The results suggest that bond strength decreases with an increase in the content of nickel powder. At 0.3 vol% of nickel coating, we found the nature of nickel to be less efficient in terms of bond strength. A different picture arose when the content of nickel was increased and the bond strength increased in nickel coated samples. In addition, the results demonstrate that mechanical properties such as bend strength are strongly dependent on bond strength.

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

The matrix accumulative roll bonding technology （MARB） can improve the matrix performance of metal composite and strengthen the bonding quality of the interface./n this research, for the fwst time, the technology of MARB was proposed. A sound Cu/AI bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope （SEM） and energy-dispersive spectroscopy （EDS）. The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/AI composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/AI composite with sound interface was obtained as well.

Fabrication of an in-situ nanoAl_2O_3/Cu composite with high strength and high electric conductivity

A heat-resistant dispersion-strengthening nano-Al_2O_3/Cu composite with highstrength and high electric conductivity was fabricated in a multiplex medium. The internaloxidation product, microstructures and properties of the composite, and the process flow weresystematically studied. It is confirmed that this new technique simplifies the process and improvesthe properties of the composite. X-ray analysis indicates that the alumina particles formed duringinternal oxidation consist of a large mount of gamma-Al_2O_3 and a certain amount of theta-Al_2O_3and alpha-Al_2O_3. TEM observation shows that the obtained gamma-Al_2O_3 nano-particles areuniformly distributed in the copper grains; their mean size and space between particles are 7 runand 30 nm, respectively. The main properties of the composite with 50 percent cold deformation areas follows: the electric conductivity is 51 MS/m (87 percent IACS), sigma_b = 628 MPa, and thehardness is HRB86. After annealing at 1273 K, all or most of the above properties remain, and themicrostructures are still dependent on elongated fiber-form grains.

Self-propagating High-temperature Synthesis, Microstructure and Mechanical Properties of TiC-TiB_2-Cu Composites

TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composites were investigated. The X-ray diffraction （XRD） and scanning electron microscopy （SEM） results showed that the final products were only TiC, TiB2 and Cu phases. The clubbed TiB2 grains and spheroidal or irregular TiC grains were found in the microstructure of synthesized products. The reaction temperature and grain size of TiB2 and TiC particles decreased with increasing Cu content. The introduction of Cu into the composites resulted in a drastic increase in the relative density and flexual strength, and the maximum values were obtained with the addition of 20 wt pct, while the fracture toughness was the best when Cu content was 40 wt pct.

Microstructure and mechanical properties of SiC-particle-strengthening tri-metal Al/Cu/Ni composite produced by accumulative roll bonding process

In this study, a multilayer Al/Ni/Cu composite reinforced with Si C particles was produced using an accumulative roll bonding(ARB) process with different cycles. The microstructure and mechanical properties of this composite were investigated using optical and scanning microscopy and hardness and tensile testing. The results show that by increasing the applied strain, the Al/Ni/Cu multilayer composite converted from layer features to near a particle-strengthening characteristic. After the fifth ARB cycle, a composite with a uniform distribution of reinforcements(Cu, Ni, and SiC) was fabricated. The tensile strength of the composite increased from the initial sandwich structure to the first ARB cycle and then decreased from the first to the third ARB cycle. Upon reaching five ARB cycles, the tensile strength of the composite increased again. The variation in the elongation of the composite exhibited a tendency similar to that of its tensile strength. It is observed that with increasing strain, the microhardness values of the Al, Cu, and Ni layers increased, and that the dominant fracture mechanisms of Al and Cu were dimple formation and ductile fracture. In contrast, brittle fracture in specific plains was the main characteristic of Ni fractures.

Thermal expansion and mechanical properties of high reinforcement content SiC_(p)/Cu composites fabricated by squeeze casting technology

High reinforcement content SiCp/Cu composites (φp=50%, 55% and 60%) for electronic packaging applications were fabricated by patent cost-effective squeeze-casting technology. The composites appear to be free of pores, and the SiC particles are distribute uniformly in the composites. The mean linear coefficients of thermal expansion (CTEs, 20-100 ℃ ) of as-cast SiCp/Cu composites range from 8.8×10-6 ℃-1 to 9.9×10-6 ℃-1 and decrease with the increase of SiC content. The experimental CTEs of as-cast SiCp/Cu composites agree well with the predicted values based on Kerner model. The CTEs of composites reduce after annealing treatment due to the fact that the internal stress of the composite is released. The Brinell hardness increases from 272.3 to 313.2, and the modulus increases from 186 GPa to 210 GPa for the corresponding composites. The bending strength is larger than 374 MPa, but no obvious trend between bending strength and SiCp content is observed.

Preparation and Arc Erosion Resistance of C_f/Cu Composite by Vacuum Melting Infiltration

Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/ C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared C/Cu bad better ability to resist the arc erosion, compared with common Cu-C material.

Reaction thermodynamics and kinetics on in situ Al_2O_3/Cu composites

The preferred internal oxidation of aluminum in Cu Al alloy was used to obtain in situ Al 2O 3/Cu composites. The reinforcement particles were mainly γ Al 2O 3, some θ Al 2O 3 and a little α Al 2O 3. Thermodynamics analyses show that the chemical reactions are 3Cu 2O+2Al=6Cu+Al 2O 3 or 3CuO+2Al=3Cu+Al 2O 3. A related equilibrium diagram was drawn. The experiments and investigation show that the formation rate of Al 2O 3 was controlled by the diffusion of oxygen in matrix.

Tribological behavior of CNTs-Cu and graphite-Cu composites with electric current

CNTs-Cu and graphite-Cu composites were separately prepared by powder metallurgy technique under the same consolidation processing. Tribological behavior of the composites with electric current was investigated by using a pin-on-disk friction and wear tester. The results show that the friction coefficient and wear rate of the composites decrease with increasing the reinforcement content, and increase with increasing the electric current density; the effects of electric current are more obvious on tribological properties of graphite-Cu composites than on CNTs-Cu composites; for graphite-Cu composites the dominant wear mechanisms are electric arc erosion and adhesive wear, while for CNTs-Cu composites are adhesive wear.

A Novel Technique for Preparation of Electrically Conductive ABS/Cu Polymeric Gradient Composites

A novel technique for preparing functionally gradient electrically conductive polymeric composites was developed by using of solution casting technique on the principle of Stokes＇ law. Acrylonitrile- butadiene-styrene/Cu （ABS/Cu） gradient polymeric composites were prepared successfully using this technique. The gradient structures, electrically conductive performance and mechanical properties of the ABS/Cu composites were investigated. Optical microscope observation shows that the gradient distribution of Cu particles in ABS matrix was formed along their thickness-direction. The electrically conductive testing results indicate that the order of magnitude of surface resistivity was kept in 10^15 Ω at ABS rich side, while that declined to 10^5 Ω at Cu particles rich side, and the percolation threshold was in the range of 2.82 vo1%- 4.74 vol% Cu content at Cu particles rich side. Mechanical test shows that the tensile strength reduced insignificantly as the content of Cu increases owing to the gradient distribution.