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Production of Copper Matrix Composites Reinforced with Aluminum Oxide Particles by In-Situ (Mechanical Alloying and Internal Oxidation) and Ex-Situ Methods

Tahan Zadeh, Samira | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47168 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Purazarng, Kazem; Abachi, Parvin
  7. Abstract:
  8. In this study, copper-alumina composite specimens with different reinforcement content were produced in two routes, i.e. in-situ and ex-situ; one specimen as functionally graded material (FGM) was also produced. In first method, copper and aluminum powders were initially alloyed by mechanical alloying route and then the copper oxide powder was added as oxidizer. For the fabrication of Cu-Al2O3 composites using ex-situ method, alumina nano particles powder was added to elemental copper powder. FGM specimen consists of five layers, i.e. pure copper, copper matrix composite having 2, 3, 4, and 5 volume percent alumina. To reduce the particles agglomeration and homogeneous distribution of reinforcement particles in copper matrix, high energy ultrasonic device was used to mix copper and alumina particles for 15 min. Neutral liquid ethanol as PCA was used to better dispersion of particles. Then, copper and alumina powders were stirred in the turbulence mixer for an hour. To ensure the exact compositional distribution within the layers, each layer was firstly compacted under a lower pressure before stocking of the adjacent layer under higher pressure, 100 MPa. To increase the density of raw specimens, spark plasma sintering (SPS) method was used. Sintering was performed at 700-800 °C for 5-6 minutes under the argon atmosphere and pressure of 30 MPa. In order to remove additional materials as PCA and degassing, initially, each powder mixture was kept in 0.4 of copper melting point, approximately in temperature range of 380-390 °C for 5-10 min. During sintering, cooling and heating rate was 25 and 40 °C/min, respectively. At first, the effect of fabrication method on the microstructure and distribution of reinforcement particles was studied. Then, the effect of microstructure on some physical properties such as density, specific electrical resistance and mechanical properties such as hardness and wear resistance of composites was examined. In order to study dissolution procedure of aluminum in copper lattice, XRD pattern was prepared in certain periods of time and SEM was used to study and evolute size and morphology of milled powders. The density of samples was determined based on the Archimedes principle, using special kit and balance with precision 0.0001gr. The hardness of composite specimens was measured in Vickers and Brinell scales based on ASTM E92 and ASTM E10 by applying load of 20N and 31.25N for 30s, respectively. The electrical resistivity of specimens was measured using Micro Ohmmeter, then specific electrical resistivity and electrical conductivity were calculated. To evaluate the abrasion resistance of composites, pin-on-disk wear test according to ASTM G-99 standard for pure copper samples and composite specimens produced in-situ and ex-situ method was performed under constant speed of 4.0 m/s and applied load of 20, 30 and 50 N and four sliding distance of 200, 400, 600 and 800 meters. The results of hardness measuring showed that with increasing volume fraction of reinforcement particles, the hardness of samples increases. Also, the results of electrical resistance measurment showed that with increasing volume fraction of reinforcement particles, the electrical conductivity decreases. All specimens have better abrasion resistance compared to pure copper. For all specimens, reducing the volume increased almost linearly with the applied force and the sliding distance increases. Also, by increasing the volume fraction of reinforcement particles, improves abrasion resistance of composites. For FGM specimen, a load of 20 N at the same speed and the sliding distances was used. The thickness of each layer in the FGM composite sample was obtained approximately 1 mm. According to SEM examinations of the Nano-composite specimens and cross-section of the FGM, the porosity level is low. The gradually change of structure is evident in layers of FGM from pure Cu side to Nano-composite side. Relative density value (96.97%) for FGM indicates also on significant densification due to SPS process. The lack of cracks and delaminations on the interface of layers indicates on good bonding between the layers and lack of significant harmful residual stresses
  9. Keywords:
  10. Mechanical Alloying ; Functionally Graded Materials (FGM) ; Spark Plasma Sintering ; In-situ Metal Matrix Composite (MMCs) ; Copper Alumina Nanocomposite ; Ex-Situ Copper-Alumina Composites

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