Papers by Keyword: Copper Matrix Composite

Abstract: Thermodynamic calculations indicate that molybdenum particles reinforced copper-matrix composite can be fabricated in CuO-Al-MoO3 powder system. Thermit reaction and self-propagation high-temperature synthesis (SHS) were applied to prepare samples. Then the phases, structure morphologies and properties were studied through the instruments of XRD, SEM and microhardness tester. The results show that nanocrystals are formed in Cu matrix and molybdenum particles are dispersive distributed in Cu matrix. The microhardness of 5﹪Mo-Cu nanocomposite is 110HV，and the relative electric conductivity is 58.6﹪IACS.

Abstract: Copper slag was used to prepare copper powder by way of slurry electrolysis, and the copper powder was used to fabricate copper matrix composite materials reinforced with chemical plating surface modified alumina particulates. Alumina particulates were pretreated in ultrasonic field by chemical copper plating in order to make alumina particulates covered with a layer of copper film and form Al2O3/Cu composite powders. Copper matrix composite materials strengthened with alumina particulates were synthesized by means of pressure molding and sintering. Microstructure of copper matrix composites was researched by means of SEM. SEM analysis shows that alumina particulates distribute in the copper-based body evenly, and combine with copper closely. The effects of sintering temperature, pressure and alumina content on the compactness and hardness of copper matrix composites were studied by orthogonal tests. The compactness of composites increases with the sintering temperature and pressure increasing, and decreases with the alumina content increasing. The hardness of composite materials increases with the sintering temperature, pressure and alumina particulates increasing.

Abstract: An in-situ composite of copper and tungsten carbide powder was prepared by mechanical alloying of elemental powder. The sample has been milled in a high-energy ball mill for 20 h at different milling speed i.e. 100, 200, 300 and 400 rpm in an argon atmosphere. Investigations in terms of microstructural features and phase constitution of in-situ composites powder were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At higher milling speed, W2C is found to be precipitated with a small amount of WC was formed. Crystallite size of copper is reducing while internal strain is increasing with increasing milling speed.

Abstract: Today, there is a strong push to improve the thermal management of electronic components in order to increase the performance and the reliability of electronic devices. Up to now, most of the heat sinks are mainly made of Copper that presents a good thermal conductivity (TC) but a coefficient of thermal expansion (CTE) much higher than the ceramic of the DBC (direct bonding Copper). It induces interfacial thermal stresses and indeed it decreases the reliability of the global electronic system. Therefore, there is a strong need for the development of novel heat dissipation material having low CTE combined with high TC. Carbon fibres reinforced copper matrix offers a good compromise between thermo mechanical properties (i.e. CTE) and medium TC. In order to increase surface TC, pure Copper can be added on the top surface and/or on the bottom one of the composite heat sink playing the role of heat spreader for hot spots linked with the Si components. The fabrication technique of these materials is based on powder metallurgy technique. The thermal properties of adaptive materials, TC and CTE, have been measured for different Copper thicknesses and architectures ([C/Cu], [Cu – C/Cu] and [Cu – C/Cu – Cu]). Simulation of the TC and CTE have been performed and compared to the experimental results.

Abstract: The nano-Al2O3 reinforced copper matrix composite was prepared by powder metallurgy technique and the fretting test against 440C stainless steel was performed at room temperature by using the ball-on–flat configuration with 300μm amplitude at various normal loads in the range of 0.1N to 1N. The influences of load and proportion of Al2O3 on the friction coefficient and volume wear -loss were investigated. Results showed that the volume wear-loss decreased firstly and then increased as the proportion of Al2O3 increased from 0.5% to 4%, and the minimum proportion was about 2%, in which the electrical conductivity can reach up to 81% according to International Annealed Copper Standard (IACS). The friction coefficient of the copper will slightly increases as the load increased. However, in the case of composites, it increased firstly then decreased. The volume wear-loss of the composite is always lower than that of copper, giving the highest relative wear-ability of 1.55, which indicated a higher wear resistance. The wear mechanism of copper is adhesive wear, whereas it becomes oxidation wear in composites.

Abstract: CP-Nb-Cr/Cu-Cd electrical contact material, which contains 1.7wt.% of Cd, 0.5wt.% of CP (man-made diamond particles), 2.0 wt.% of Nb and 0.7 wt.% of Cr, was fabricated by powder metallurgy process. The contact material was installed in different ac contactors covering current range from 40 to 630A. While tested under AC-4 electrical load, the electrical contact material was worn out gradually by repeated electrical arc, and microstructure of the arc-affected surface layer changed dramatically. Mechanism of arc erosion process and contact resistance fluctuation was discussed by corresponding microstructure observation and chemical composition analysis of the surface layer. CP-Nb-Cr/Cu-Cd electrical contact material is capable to be used in 63~250A ac contactors under AC-4 working conditions.

Abstract: Composites materials consisting of pure copper reinforced with 1 vol.% of NbC were prepared by the powder metallurgy route to determine the influence of the milling process on the mechanical and electrical properties. For comparative purpose different milling times at four different rotational speeds were used. The resulting powders were consolidated by hot uniaxial pressing under 90MPa for 2h at 923K to obtain materials with a fine microstructure without residual porosity. It was found that the microstructure and properties of composite materials could be principally related to the amount of Fe, Cr, C and O incorporated as impurities during the milling process. Therefore, the rotational speeds used for milling has an important influence on the properties of the final product. A lower energy-ball milling is accompanied by a smaller amount of impurities (Fe, C and O) incorporated during milling. Composites materials combine electrical conductivity above 40% IACS with high strength. A detailed microstructural analysis by scanning and transmission electron microscopy and X ray diffraction showed that these properties are related not only to NbC particles, but also to the presence of very fine particles of carbides and oxides.

Abstract: A copper matrix composite reinforced with in situ TiB2 nanoparticle was successfully fabricated by tubulent in-situ mixing process. The microstructure, mechanical and electrical properties of the in situ composite were investigated. The results showed that the in situ formed TiB2 particles, in which size varying from about 50nm to 200nm, exhibited a homogenous dispersion in the copper matrix. It is shown that the interface between the nanoscale particles and the matrix was clean without a transitional layer. Because of the reinforcement, the hardness and Young’s Modulus of the composite improved with increment of cooling rate. Moreover, the in situ Cu-TiB2 composite exhibited higher electrical conductivity with increasing of cooling rate.

Abstract: Preparation of titanium diboride reinforced copper matrix composites with high conductivity and mechanical strength was developed based on in situ produced powders. The effect of the titanium diboride content on the mechanical properties of the bulk material produced from the powders by Spark Plasma Sintering technique was studied. Increasing titanium diboride content from 2.5 up to 7.5 wt.% resulted in a 1.5-fold increase in yield strength, tensile strength and hardness and 5-fold increase in wear resistance with only 10% decrease in conductivity.

Abstract: Cu-TiB2 nanocomposite powders were in situ synthesized by combining high-energy ball milling of Cu-Ti-B elemental powder mixtures as precursors and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.% TiB2 was produced after SHS reaction and then diluted by copper to obtain desired homogeneous composites with 2.5, 5 and 10wt.%TiB2. Spark plasma sintering (SPS) was used to inhibit grain growth and thereby obtain fully Cu-TiB2 sintered bodies with nanocomposite structure. After SHS reaction, only Cu and TiB2 phases were detected in the SHS-product. Spheroidal TiB2 particles smaller than 250nm were formed in the copper matrix after SHS-reaction. Mechanical and electrical properties were investigated after SPS at 650°C for 30min under 50MPa. The electrical conductivity decreased from 75 to 54% IACS with increasing of TiB2 contents from 2.5 to 10wt.%. However, hardness increased from 56 to 97HRB. In addition, the tensile strength increased with increasing the TiB2 content.