Cu-Al2O3 Composites Research Articles

Preparation and microstructure of Cu-Al2O3 composites by a novel supercritical water liquid phase in-situ reaction method

The high solubility, reactivity and solubility of supercritical water provide a new way for the preparation of advanced metal matrix composites. In this paper, Cu-Al2O3 composites are prepared by supercritical water liquid phase in situ reaction (SW-LIR). In this method, the Cu-Al atomized alloy powder are used as raw material, deionized water as reaction medium, H2O2 as liquid phase oxygen source, and the Cu-Al2O3 composite powder are prepared at 380 ℃ and 22.1 MPa for 10 min. The Cu-Al2O3 composite block is prepared by spark plasma sintering (SPS). The results show that Al2O3 has an average size of 41.8 nm and mainly exists in the form of mixed crystals. The interface with the matrix is coherent or semi-coherent. With the increase of Al2O3 content, the mechanical properties of the composites are obviously improved. When the Al2O3 content is 1.12 wt%, the microhardness is as high as 164.52 HV and the tensile strength is 441 MPA, while still maintaining a high electrical conductivity (75 %IACS). At the same time, it shows quite excellent high temperature performance. It can still retain the characteristics of high strength at 1000℃, which solves the shortcomings of high thermal conductivity but low strength of pure copper. Compared with the traditional method, SW-LIR method has the characteristics of low reaction temperature, fast reaction speed and green environmental protection.

Interfacial reactions in actively brazed Cu-Al2O3 composites and copper using a newly developed Cu-Sn-Ag-Ti filler alloy

In dissimilar brazing, the differences in physical properties between the components lead to residual stresses. An active filler alloy Cu-20.5Sn-20Ag-3.5Ti was developed to braze the Cu-Al2O3 composites (containing 25 and 50 volume pct. Al2O3) to copper. Two mechanisms were proposed for chemical bonding as a result of alumina reinforcements reduction by the active titanium, including the formation of Ti3(Cu,Al,Sn)3O layer beside the Ti2O in Cu/Cu-25%Al2O3 joints; and the solidification of Ti3(Cu,Al,Sn)3O in the vicinity of TiO layer/Cu4Ti islands in the Cu/Cu-50%Al2O3 joints. Some intermetallic compounds such as Cu3Ti2 and Cu41Sn11 are formed/coarsened with an extra increase in brazing temperature. An increase in brazing time improves the thickness of the TiOx layer with no sensible effect on Ti3(Cu,Al,Sn)3O width.

Fabrication of Multiscale-Alumina Particles Reinforced Copper Matrix Composites with High-Energy Ball Milling and Hot Pressing

Cu-Al2O3 composite materials combining the good electrical of copper matrix and the high hardness of Al2O3 ceramic particles show great performance in electronics, electrical sliding contacts fields. However, the relationship of a dilemma between strength and ductility has become a limitation for the development of copper matrix composites. The previous works indicated that fine grain powders can improve interfacial bonding between the copper matrix and Al2O3 particles to further enhance strength while maintaining ductility. In the present work, the multiscale-alumina particles reinforced copper matrix composites were successfully fabricated by mixing high-energy ball milling and consolidation of hot-press sintering. SEM and TEM were used to observe the powder morphology and microstructure of Cu-Al2O3 composites. The results show that the reinforcing phase Al2O3 particles are uniformly dispersed in the copper matrix, which improves interfacial bonding between the copper matrix and Al2O3 particles. Especially, the micro Al2O3 particles play an important role in achieving an excellent tradeoff of strength and ductility in the Cu-Al2O3 composite. In addition, the microhardness of Cu-Al2O3 composites can be greatly improved by using the high-energy ball milling and hot-press sintering process. The research idea of this paper can provide a reference for other composite materials that need to improve mechanical properties.

Effect of nano Al2O3 coated Ag reinforced Cu matrix nanocomposites on mechanical and tribological behavior synthesis by P/M technique

In this study, copper powder was reinforced with different weight percentages of Al2O3 particles (0, 5, 10, and 15 wt.% Al2O3 coated Ag) to produce Cu-Al2O3 composites by mechanical alloying and uniaxial cold pressing/sintering route. Electro-less deposition was used to coat Al2O3 particles with Ag. The microstructure of the consolidated samples was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) elemental mapping. The porosity, microhardness, and wear behavior of the consolidated samples were also investigated as a function of Al2O3 content. The EDX mapping images reveal that the Al2O3 reinforcement particles were homogeneously distributed into the Cu matrix. Microstructural analysis shows that the addition of Al2O3 coated Ag particles improves density of the composites coating. SEM micrographs result shows that slight porosities exist in the composites produced. Furthermore, the average hardness of the composite coatings varies from 72.3 to 187.6 HV as Al2O3 content increases from 0 to 15 wt.%. The wear test results showed that the composite with higher Al2O3 content 15 wt.% showed the best wear resistance.

Enhancing the oxidation resistance and electrical conductivity of alumina reinforced copper-based composites via introducing Ag and annealing treatment

Alumina-reinforced copper matrix composites with Ag addition were fabricated by internal oxidation. The effects of slight Ag addition (0.92 at%) on electrical conductivity (EC) and oxidation resistance of internal-oxidized copper alumina composites were investigated. The annealing treatments were carried out to promote the diffusion of Ag in copper matrix. Ag was observed to segregate at Cu/Al2O3 interface after being annealed, which may lead to the lower interfacial energy between Al2O3 and copper matrix. The EC increased more than 7.8% after Ag was added. Moreover, annealing CuAl2O3Ag composite at 500 °C for 10 h results in the improvements of both oxidation resistance and EC. The initial oxidation temperature increased from 169 °C to 189 °C and the EC increased from 81.98 ± 0.56% International Annealed Copper Standard (IACS) to 88.19 ± 0.27%IACS. While the EC of CuAl2O3 composites always remained ∼76%IACS which suggests that the annealing treatment has insignificant impacts on EC of CuAl2O3 without Ag.

Influence of lanthanum on enhancement of mechanical and electrical properties of Cu-Al2O3 composites

Two kinds of Cu-Al2O3 composites (with and without La) were prepared via mechanical alloying-spark plasma sintering (MA-SPS) method. Microstructure, mechanical properties and electrical resistivity were investigated systematically using metallography, scanning electron microscopy, transmission electron microscopy, mechanical and electrical properties testing. The results indicate that an appropriate amount of La can homogenize the distribution of Al2O3. As such, yield strength, ultimate tensile strength and elongation of Cu-Al2O3-La are greatly increased. Some semi-coherent interface between Cu and Al2O3 is found, which means a low interface energy. The grain shape of Cu changes to irregular band with the addition of La. This change results in a density decrease of grain boundary and reduces electrical resistance. Lanthanum may exist in the form of La2O3.

The effect of reinforcement particle size on the properties of Cu-Al2O3 composites

abstractThe main aim of this paper was to investigate the effect of reinforcement particle size on the properties of Cu-Al2O3 composites. The starting materials for obtaining the composites were commercial powders: Cu and Al2O3. Experiments were performed using specimens containing 2.5, 5, 7.5 and 10 % of alumina. The average particle sizes of alumina were 3.5, 22.5, and 65 μm. Before the sintering process, single pressing was performed with a hydraulic press at a compaction pressure of 620 MPa. The obtained sinters were subjected to the compaction process at a pressure of 620 MPa, and then again sintered at 900 °C for 60 minutes. The sintering process was carried out for 60 minutes at a temperature of 900 °C. The sintered compacts were subjected to the following tests: measurement of density, hardness and electrical conductivity. Observations of the microstructure on metallographic specimens made from the sintered samples were also performed using a scanning electron microscope (SEM). The density of all the composites increased when the particle size of alumina was reduced. Higher hardness were observed in samples containing finer Al2O3 particles. The electrical conductivity of the fabricated composites increased with the reduction of the alumina particle size.

Near-Net Shape Manufacturing of Copper-Ceramic Composites Via Gas Pressure Infiltration in Permanent Molds

Abstract Composites with a interpenetrated copper-ceramic microstructure can be customized for highest demands such as a high thermal conductivity in combination with a small thermal expansion. This article reports on the synthesis of near-net shape Cu-Al2O3 composites via gas pressure infiltration. Open-porous Al2O3 preforms are infiltrated with Cu using Si3N4 permanent molds. The infiltration quality as well as the porosity distribution within the materials are described qualitatively and quantitatively. The effects of the manufacturing process and cooling rate on the composites will be looked at.

Influence of Ag addition on the microstructure and properties of copper-alumina composites prepared by internal oxidation

In present study, Cu-Al2O3 composites with both higher micro-hardness and electrical conductivity were fabricated by internal-oxidizing Cu-Al and Cu-Al-Ag sheets at 950 °C for 2 h. A small amount of Ag was doped as additives with atomic ratio of Ag/Al ranging from 0 to 0.25. Effects of Ag addition on microstructures, electrical conductivity and micro-hardness were investigated. Results show that the morphology and size distribution of Al2O3 in internal-oxidized Cu-Al alloys were highly sensitive to Ag addition. The size of Al2O3 precipitates decreased from ∼63 nm to ∼37 nm when increasing Ag content. Moreover, a large number of triangular Al2O3 precipitate with similar size was observed by field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscopy (HRTEM) in Ag-doped Cu-Al2O3 composites. The orientation relationship between triangular Al2O3 and Cu matrix was [112]Cu//[110]Al2O3, (111¯)Cu//(002)Al2O3 and (22¯ 0)Cu//(22¯ 0)Al2O3. Increasing the amount of Ag enhances the electrical conductivity and mechanical strength simultaneously. The optimal electrical and mechanical properties which were 85.9% IACS and 162 HV respectively, were obtained when atomic ratio of Ag/Al was ∼1:4 in internal-oxidized Cu-Al2O3-Ag alloy.

Hardness, Electrical Conductivity and Thermal Stability of Externally Oxidized Cu-Al2O3 Composite Processed by SPD

Cu-Al2O3 composites prepared by external oxidation method were further enhanced by severe plastic deformation (SPD) processing, including equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) methods. The HV hardness and electrical conductivity of the samples before and after SPD processing were tested. Results revealed that ECAP samples (with an equivalent strain of about 5.34) showed a relative small increase in hardness, whereas a significant decrease in electrical conductivity. The HPT samples (with an equivalent strain of about 6.94) showed not only a much improved hardness but also a higher electrical conductivity. Thermal stability of the SPD-processed Cu-Al2O3 composites was tested, and the HPT samples maintained good HV hardness together with high electrical conductivity even at 600 °C. The combination of external oxidation method and HPT processing resulted in enhanced mechanical properties, good electrical conductivity, acceptable thermal stability, and much simplified oxidation process.

The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)

In order to meet the requirements of an increased efficiency applying to modern devices and in more general terms science and technology, it is necessary to develop new materials. Combining various types of materials (such as metals and ceramics) and developing composite materials seem to be suitable solutions. One of the most interesting materials includes Cu-Al2O3 composite and gradient materials (FGMs). Due to their potential properties, copper-alumina composites could be used in aerospace industry as rocket thrusters and components in aircraft engines. The main challenge posed by copper matrix composites reinforced by aluminum oxide particles is obtaining the uniform structure with no residual porosity (existing within the area of the ceramic phase). In the present paper, Cu-Al2O3 composites (also in a gradient form) with 1, 3, and 5 vol.% of aluminum oxide were fabricated by the hot pressing and spark plasma sintering methods. Two forms of aluminum oxide (αAl2O3 powder and electrocorundum) were used as a reinforcement. Microstructural investigations revealed that near fully dense materials with low porosity and a clear interface between the metal matrix and ceramics were obtained in the case of the SPS method. In this paper, the properties (mechanical, thermal, and tribological) of composite materials were also collected and compared. Technological tests were preceded by finite element method analyses of thermal stresses generated in the gradient structure, and additionally, the role of porosity in the formation process of composite properties was modeled. Based on the said modeling, technological conditions for obtaining FGMs were proposed.

The Influence of the Particle Size on the Adhesion Between Ceramic Particles and Metal Matrix in MMC Composites

This study investigated the influence of the particle size on the adhesion force between ceramic particles and metal matrix in ceramic-reinforced metal matrix composites. The Cu-Al2O3 composites with 5 vol.% of ceramic phase were prepared by a powder metallurgy process. Alumina oxide powder as an electrocorundum (Al2O3) powder with different particle sizes, i.e., fine powder <3 µm and coarse powder of 180 µm was used as a reinforcement. Microstructural investigations included analyses using scanning electron microscopy with an integrated EDS microanalysis system and transmission microscopy. In order to measure the adhesion force (interface strength), we prepared the microwires made of the investigated materials and carried out the experiments with the use of the self-made tensile tester. We have observed that the interface strength is higher for the sample with coarse particles and is equal to 74 ± 4 MPa and it is equal to 68 ± 3 MPa for the sample with fine ceramic particles.

Processing, Microstructure and Properties of Different Method Obtained Cu-Al2O3 Composites/ Wytwarzanie, Mikrostruktura I Właściwości Kompozytów Cu-Al2O3 Otrzymywanych Róznymi Technikami

Abstract Alumina/copper composites are used where high thermal conductivity, high absorption and dissipation of heat, high resistance to thermal fatigue and good frictional wear resistance are required. The properties of these composites depend on a number of factors including the content, shape and distribution of the ceramic phase, the method of their obtaining, as well as the conditions under which they are obtained. All these variables have influence on mentioned properties and, in consequence, on the future applications of the final material. The aim of this paper was to develop Cu-Al2O3 composites, processed using two techniques, namely sintering (of Cu /Al2O3 high-energy mixed powders) and tape casting (of slurry of the following composition: 1, 3 and 5 vol.% of Al2O3 phase; the remaining part: Cu). The compositions were determined taking into consideration the planned applications. The paper presents newly developed technologies, the results of both microstructure investigations as well as of the measurements of selected physical and mechanical properties (microhardness, wear resistance, thermal conductivity etc.) and contains the analysis of the influence of selected techniques and processing conditions on the properties and the interface morphology between ceramic and copper

Physical Properties of Copper Based MMC Strengthened with Alumina

Abstract The aim of this work is the development of Cu-Al2O3 composites of copper Cu-ETP matrix composite materials reinforced by 20 and 30 vol.% Al2O3 particles and study of some chosen physical properties. Squeeze casting technique of porous compacts with liquid copper was applied at the pressure of 110 MPa. Introduction of alumina particles into copper matrix affected on the significant increase of hardness and in the case of Cu-30 vol. % of alumina particles to 128 HBW. Electrical resistivity was strongly affected by the ceramic alumina particles and addition of 20 vol. % of particles caused diminishing of electrical conductivity to 20 S/m (34.5% IACS). Thermal conductivity tests were performed applying two methods and it was ascertained that this parameter strongly depends on the ceramic particles content, diminishing it to 100 Wm-1K-1 for the composite material containing 30 vol.% of ceramic particles comparing to 400 Wm-1K-1 for the unreinforced copper. Microstructural analysis was carried out using SEM microscopy and indicates that Al2O3 particles are homogeneously distributed in the copper matrix. EDS analysis shows remains of silicon on the surface of ceramic particles after binding agent used during preparation of ceramic preforms.

Application of Ceramic Preforms to the Manufacturing of Ceramic - Metal Composites

Abstract This paper presents new solution to manufacturing Cu-Al2O3 composites with a dispersed reinforcement phase. It consists in substituting commonly used commercial alumina powder with crushed ceramic foam. Very low strength of thin-walled Al2O3 porous foams results in both their easy destruction and isolation of fragments &lt;200 μm. The addition of the ceramic phase is 3-10 vol.%. The sintering process is performed for 30 min in a hot-press at 1050°C and 30 MPa. The aim of the presented paper is to study the effect of the volume content of the ceramic phase on the microstructure and selected physical and thermal properties of copper - alumina composites.

The Microstructural Effects on the Mechanical and ThermalProperties of Pulsed Electric Current Sintered Cu-Al2O3 Composites

In this work, the influences of the microstructure on the mechanical and thermal properties of pulsed electric currentsintered (PECS) Cu-Al2O3 composites are investigated. The process parameters were optimized for four different grades ofcomposite powders to obtain dense samples (98-99.6%T.D.). Higher hardness and better thermal stability were attained tothe samples compacted from commercial internally oxidized (IO) powders than to the compacts made from the chemicallysynthesised experimental powders. This difference was attributed to the distribution and size of Al2O3-particles in the twotypes of composites. The CTE values of all the compacts were between 17 and 20 x 10-6K-1 (370-770K). The results showthat PECS can be used to produce dense high quality Cu-Al2O3 composites.

Analysis of Functional Properties of Cu-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Particulate Reinforced Composites. A First Assessment: Elaboration

The possibilities of Cu-Al2O3 particulate reinforced composites, of competitive functional properties, processing by the classical powder metallurgy route have been investigated taking into consideration its known technical and economical advantages in respect to the known worldwide investigated technological routes of their processing. The adopted compositions, of (5.0÷20.0) [vol.%] Al2O3, were selected in agreement with published data for a large range of applications. Pharmaceutical homogenization method applied for powder mixtures preparation proved to assure a high homogeneity, evidenced by SEM and EDS analyses. Their determined compressibility has shown that, for all compositions, the obtainable compactness is very close to that of pure Cu (even over 94 %). Cold uniaxial compaction at 500 and 700 MPa, and subsequent sintering in argon of high purity at 800 °C for 45 and 60 min have been adopted for composites realization. The performed analysis of the compacting pressure and sintering time influence on the composite compactness proved that, beside the above specified values obtaining for 700 MPa and 60 minute processing parameters, high enough values, acceptable for numerous applications, can be also obtained at 500 MPa and 60 or even 45 minutes. Finally, microstructural analysis highlighted that, by the adopted processing conditions, a high uniformity of Al2O3 particles distribution in the Cu matrix can been assured, both creating premises for obtaining good functional properties of Cu-Al2O3 composites, proving the competitiveness of the investigated PM route for their elaboration.

Fabrication of Cu-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Composites by Simplified Internal Oxidation Process

Cu-Al2O3 composites were prepared by a new simplified internal oxidation process integrating with powder metallurgical process, and then the hot extrusion and the cold rolling processes were carried out. The microstructure, electrical conductivity, hardness, tensile strength and thermal stability of the composites were investigated. The results show that Cu-Al2O3 composites were fabricated successfully by the simplified process in which internal oxidation completed during the sintering. There are a mass of fine Al2O3 particles in size varying from 5 nm to 20nm dispersed in copper matrix after sintering 950 for 4h. After sintered at 950 for 4h and extruded at 950 followed with the cold deforming of 80%, the electrical conductivity, hardness, tensile strength and softening temperature of composite reach 81％IACS, 137HV, 561MPa and 850 respectively. It is considered that the dispersion strengthening and strain hardening have greatly contribution to the Cu-Al2O3 composites fabricated with the simplified process.

Synthesis and Characterization of Cu and Ni Bearing Nano-Composites and Nano-Structured Alloys

It is well recognized the importance of nano-structured materials in the present technological stage. Due to their unique properties these materials can be used in a large number of applications. One example is the growing interest in nanocomposites, in which a very fine dispersion of a ceramic phase in a metal matrix will significantly improve the material properties. In view of that, extensive studies have been carried out on a variety of materials such as alloys and different types of composites. Recently, the authors have developed a novel chemical method for in-situ formations of Cu-Al2O3 and Ni-Al2O3 nanoscale composites by decomposition of their mixed nitrate solutions, to co-form the nano oxides, followed by preferential reduction of CuO or NiO by hydrogen at very low temperature. Studies carried out by the authors on the kinetics of reduction of such fine oxides indicated that under low partial pressure of hydrogen (0.25 atm) in argon, the oxides of Ni and Cu can be reduced completely, in a low temperature range of 523 to 623 K. The composites containing nanosized metal-metal oxide particles have been found to be quite homogeneous in nature. In view of this, Cu-Ni and Ni-Co alloys was also produced by mixing the respective aqueous nitrate solutions, followed by decompositions of their nitrates to their mixed oxides and subsequent low temperature hydrogen reduction. In that context, the purpose of the present work is to address the fundamental aspects of the synthesis procedure, emphasizing the basic thermodynamics background of the two steps involved. Also, the work aims to illustrate the outcome, by presenting experimental conditions and providing relevant characterization of the obtained nano-materials, by means of electronic microscopy and X-Ray Diffraction. Examples are given in terms of the obtained nano-composites and alloys.

Characteristics of Cu-Al2O3 composites of various starting particle size obtained by high-energy milling

The powder Cu-Al2O3 composites were produced by high-energy milling. Various combinations of particle size and mixtures and approximately constant amount of Al2O3 were used as the starting materials. These powders were separately milled in air for up to 20 h in a planetary ball mill. The copper matrix was reinforced by internal oxidation and mechanical alloying. During the milling, internal oxidation of pre-alloyed Cu-2 mass %-Al powder generated 3.7 mass % Al2O3 nano-sized particles finely dispersed in the copper matrix. The effect of different size of the starting copper and Al2O3 powder particles on the lattice parameter, lattice distortion and grain size, as well as on the size, morphology and microstructure of the Cu-Al2O3 composite powder particles was studied.