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The aim of the article was to evaluate the microstructural parameters of Cu–Al2O3 dispersion strengthened materials with different volume fraction of Al2O3 phase. For analyses of dispersoids Al2O3, the extraction carbon replica was used. The distribution of Al2O3 particles in the matrix was estimated by three methods (quadrant count method, polygon...
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Citations
The extraction replica technique is a useful sample preparation method to fabricate transmission electron microscopy samples for subsequent studies of small particles, such as precipitates, in different types of alloys. With other sample preparation methods, such as thin foil fabrication, the surrounding matrix might influence compositional or crystallographic analysis in the TEM. The extraction replica technique omits that problem, as the precipitates are extracted onto a thin, amorphous film (most commonly carbon) and the influence of the matrix is thus eliminated. The replica can be produced in a direct manner, by a two stage-method or in certain cases by the oxide replica method. A variety of precipitates from common engineering alloys including carbides, nitrides, oxides and various intermetallic phases in steels, nickel-, zirconium-, aluminium-, copper-, and magnesium-based alloys, can be extracted and the techniques are summarized in this work. The choice of etchant is crucial for the end result, as is also showcased experimentally in this work. Furthermore, the direct replica and two-stage replica method are directly compared with each other by new experiments on a low alloyed steel and a zirconium alloy. There are indications that the direct method has a greater particle extraction efficiency of smaller particles compared to the two-stage method. Moreover, the direct method also facilitates the analysis of other features, such as grain boundaries, in special cases.
Al2O3 dispersion copper alloy powder was prepared by internal oxidation, and three consolidation methods—high-velocity compaction (HVC), hot pressing (HP), and hot extrusion (HE)—were used to prepare Al2O3 dispersion-strengthened copper (Cu–Al2O3) alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density (98.3% vs. 99.5% for HP and 100% for HE), which resulted in the lowest electrical conductivity (81% IACS vs. 86% IACS for HP and 87% IACS for HE). However, this alloy also exhibited the highest hardness (77 HRB vs. 69 HRB for HP and 70 HRB for HE), the highest compressive strength (443 MPa vs. 386 MPa for HP and 378 MPa for HE), and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.
Al2O3 dispersion copper alloy powder was made from Cu-0.18 wt%Al alloy powder and oxidant Cu2O powder through internal oxidation. Then the powder was pressed by high-velocity compaction (HVC) followed by sintering in hydrogen at 960-1080℃ to prepare dispersion strengthened copper alloy. The forming ability of the alloy powder by HVC and the effects of sintering temperature on relative density (RD), hardness, electrical conductivity as well as compressive strength were investigated. The results show that HVC pressing Al2O3 dispersion copper alloy powder could achieve good forming ability, and the green density reaches 8.72 g/cm3 (98.4%RD). Compared with the compact, RD of sintered alloy has no obvious change, while the electrical conductivity significantly improves, hardness decreases, and compressive strength increases. With increasing the sintering temperature, the electrical conductivity increases, hardness slightly decreases and compressive strength almost keeps constant. For the as-prepared alloy by sintering at 1040-1080℃, the electrical conductivity and hardness was beyond 80% IACS and 77 HRB, respectively, and compressive strength reaches 453 MPa. These properties of the alloy could basically meet the requirement of the practical application used as spot welding electrodes.
The high-velocity compaction (HVC) was applied to press three kinds of dispersion copper alloy powders with Al2O3 mass fraction of 0.34%, 1.00% and 3.19%, respectively. The forming effects of powders and the following sintered properties were studied. The results show that the relative density of green compact increases with increasing the impact energy, and decreases with increasing the Al2O3 content. When the largest impact energy is 927.5 J, the maximum relative densities of compacts of the three powders reaches 98.4%,96.2% and 93.4%, respectively. After being sintered at 1080℃ in hydrogen for 1 h, the relative density of compacts has no obvious change, the electrical conductivity is significantly improved and the hardness slightly decreases. The electrical conductivity and hardness of the prepared three Al2O3 dispersion strengthened copper alloys are 81.0%(IACS), 64.1%(IACS) and 48.3%(IACS), and 77.3, 85.7 and 81.3 HRB, respectively. After being heat-treated in hydrogen at 1080℃for 2 h, the hardness of three sintered alloys is almost unchanged. In general, the dispersion strengthened copper alloy with 0.34% Al2O3 prepared by HVC has good comprehensive performances and its electrical conductivity, hardness and softening resistance at high temperature can meet the basic requirement of the practical application used as spot welding electrodes. ©, 2015, Central South University of Technology. All right reserved.
The possibilities of Cu-Al 2O 3 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.%] Al 2O 3, 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 Al 2O 3 particles distribution in the Cu matrix can been assured, both creating premises for obtaining good functional properties of Cu-Al 2O 3 composites, proving the competitiveness of the investigated PM route for their elaboration.
This study reports some properties of copper matrix composite reinforced with silicon carbide at ratios of 1, 2, 3 and 5 % by weight manufactured by powder metallurgy method. Composite powders were pressed by applying a uniaxial pressure of 280 MPa and sintered at 900°C for 2 h in graphite powder. Optical and SEM studies revealed that SiC particles were located around Cu grains. The presence of Cu and SiC components in composites were verified by XRD analysis technique. The hardness of sintered compacts ranged from 104 to 108 HBN. The relative densities of Cu-SiC composites determined according to Archimedes' principle changed between 96.45 and 89.61 %. Electrical conductivities of Cu-SiC composites varied between 87.1 and 55.2 % IACS. As SiC content increases, hardness increases, but relative densities and electrical conductivities decrease. An attempt was made to investigate the possibility of predicting contour diagram of electrical conductivity variation.
We present a process for the production of Cu-Al matrix composites containing between 25 and 30 vol.% in situ Al2O3. The composites are prepared by pressing, heat-treating and hot working blended powders of Cu, Al and CuO packed into copper alloy cans. The evolution of the microstructure during in situ reaction is governed by the stable growth of alumina films; these mitigate the rate of reaction, preventing thermal runaway if samples are processed with sufficient thermal ballast. The resulting alumina is amenable to subsequent refinement and dispersion by hot working the composite, with reversed (extrusion/upsetting/extrusion) deformation giving best results. Cu7 wt.%Al containing homogeneously distributed micron-sized alumina particles thus produced has a tensile strength of 848±44 MPa and a tensile ductility of 2.2±0.8%.
In the present work, the process of equal channel angular pressing of dispersion strengthened Cu–1·1 wt-%Al2O3 containing nanometric alumina particles was investigated by means of mathematical modelling and experimental testing. Through the modelling, deformation parameters such as hydrostatic pressure distribution and strain field were determined, and the effect of deformation path on these parameters was estimated. Equal channel angular pressing as well as mechanical and microstructural evaluations were also conducted to assess mechanical properties, grain structure and void volume fraction after deformation in different routes. The results indicate that distributions of plastic strain and hydrostatic stresses are significantly affected by deformation path route as well as utilised die design. Furthermore, void formation around hard alumina particles may occur in regions with high tensile hydrostatic stresses leading to fracturing during deformation.
Cu-Al2O3 (Co-Al2O3) nano-array composite structures assemblies with Cu (Co) grown in the pores of an anodic alumina membrane (AAM) were obtained by alternating current electrode position. Their transmitted spectra and polarized spectra are systematically investigated. Experimental results indicate that the transmittance of Cu-Al2O3 is superior to that of Co-Al2O3 in visible and infrared waveband, but the extinction ratio of Co-Al2O3 is better than that of Cu-Al2O3 in near infrared waveband.
