Abstract
Single-crystal α-Al2O3 fibres can be utilized as a novel reinforcement in high-temperature composites owing to their high elastic modulus, chemical and thermal stability. Unlike non-oxide fibres and polycrystalline alumina fibres, high-temperature oxidation and polycrystalline particles boundary growth will not occur for single-crystal α-Al2O3 fibres. In this work, single-crystal α-Al2O3 whiskers and Al2O3 particles synergistic reinforced copper-graphite composites were fabricated by mechanical alloying and hot isostatic pressing techniques. The phase compositions, microstructures, and fracture morphologies of the composites were investigated using X-ray diffraction, a scanning electron microscope equipped with an X-ray energy-dispersive spectrometer (EDS), an electron probe microscopic analysis equipped with wavelength-dispersive spectrometer, and a transmission electron microscope equipped with EDS. The mechanical properties have been measured by a micro-hardness tester and electronic universal testing machine. The results show that the reinforcements were unevenly distributed in the matrix with the increase of their content and there were some micro-cracks located at the interface between the reinforcement and the matrix. With the increase of the Al2O3 whisker content, the compressive strength of the composites first increased and then decreased, while the hardness decreased. The fracture and strengthening mechanisms of the composite materials were explored on the basis of the structure and composition of the composites through the formation and function of the interface. The main strengthening mechanism in the composites was fine grain strengthening and solid solution strengthening. The fracture type of the composites was brittle fracture.
Highlights
Copper matrix composites have high strength, good electrical conductivity, and thermal conductivity, and show high wear resistance and a low thermal expansion coefficient [1,2,3].with the rapid development of aerospace and electronic power industries, traditional copper matrix composites can no longer satisfy the high requirements for the above-mentioned properties, and it is highly important and essential to design and study copper matrixMaterials 2018, 11, 982; doi:10.3390/ma11060982 www.mdpi.com/journal/materialsMaterials 2018, 11, 982 composites with better mechanical properties
Carbon nanotubes (CNTs) and graphene nano-sheets are widely used in copper matrix composites as reinforcement materials owing to their unique structure and excellent properties [4,5], leading to the greatly improved strength and the hardness of these composites
The purity of raw materials used in this study was greater than 99.5%, and the Alfiltration, 2 O3 whiskers were treated with a sodium dodecyl sulphate solution, followed by standing, filtration, specific particle sizes and density are shown
Summary
Copper matrix composites have high strength, good electrical conductivity, and thermal conductivity, and show high wear resistance and a low thermal expansion coefficient [1,2,3]. Addition of fine Al2 O3 particles into the copper matrix can improve the hardness of this material, and reduces the grain growth rate even at the temperatures approaching the melting point of the copper matrix [6,7] These kinds of composites are widely utilized in electronics, automobile, and aerospace fields as electrical contact materials, rocket thrusters, and components in aircraft engines, as well as in other applications [8,9]. It is necessary and sufficient to add appropriate alloying elements such as Cr, Ag, Nb, and Zr into the copper matrix for which the solid solubility decreases with the lowering of the temperature [34,35,36,37] These composites are not useful for high temperatures due to effects of recrystallization, particle coarsening and decomposition of the supersaturated solid solution [38,39]. Based on the mechanical properties and microstructure of the composites, the strengthening and fracture mechanisms were analysed
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