Investigation of the Microstructure and Mechanical Properties of Copper-Graphite Composites Reinforced with Single-Crystal α-Al2O3 Fibres by Hot Isostatic Pressing

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.

Study on corrosion resistance of copper matrix composites reinforced by Al2O3 whiskers

“…When the temperature increases from 50°C to 75°C, the corrosion reaction rate is mainly controlled by the diffusion of oxygen. As the temperature increases, the solubility of oxygen decreases, and the cathode reaction requires oxygen to participate, so the corrosion rate decreases [15]. Figure 8 is the results which can show the corrosion topography of Al 2 O 3 reinforced copper matrix composites #1, #2, #3, and #4 at 25°C with the energy spectrum results of the corresponding points.…”

“…In previous work, Al 2 O 3 whisker-reinforced copper matrix composites were prepared, in which the Al 2 O 3 whisker contents were 0, 0.5 wt%, 1 wt%, and1.5 wt%, respectively [15]. The specimens are numbered as #1, #2, #3, and #4 in order of the whisker content of Al 2 O 3 increasing (table 1).…”

“…It can be seen from figures 2(c) and (d) that the average size is10μm and it is evenly dispersed in the matrix.The gray phase is a copper matrix. The black phase is graphite, and its distribution is relatively uniform in figures 2(a) and (b), there is no agglomeration, and it is tightly bound to the matrix.With the increase of alumina whiskers, graphite aggregated greatly, the copper matrix was split, and the bond with the copper matrix was not tight enough [15]. The cracks will spontaneously initiate and continue to grow at the interface of graphite and copper matrix.…”

“…It can be seen from the figure that only the Cu peak is detected, and the peaks of Ni, Fe, C, Sn, and Pb are not found. The most intuitive phenomenon is that the XRD pattern of the sintered specimen shows a copper (311) peak, and the corresponding 2θ is 89.245° [15]. tendency decreases.Abhijeet et al [16] proposed that when the reinforcement was more inert than the matrix material, the open circuit potential would move to a positive value.…”

“…However, current researches on Al 2 O 3 reinforced copper matrix composite materials tend to focus on mechanical properties, friction and wear, rather than corrosion resistance. In the previous work of our research group, Al 2 O 3 whisker-reinforced copper matrix composites had been prepared and their mechanical properties had been studied [15]. At that time, Al 2 O 3 particles and whiskers were selected.…”