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Preparation And Properties Of Porous Si3n4 Reinforced 2024al Composites

Posted on:2011-01-20Degree:MasterType:Thesis
Country:ChinaCandidate:S C LiuFull Text:PDF
GTID:2191330338480416Subject:Materials science
Abstract/Summary:PDF Full Text Request
Si3N4/2024Al composites with reinforcement contents of 18.8-34.5vol% were prepared by pressure infiltration. Pressureless sintered porous Si3N4 ceramics were used as the preforms. The microstructures, mechanical properties and thermal properties of the obtained materials were investigated. After proper aging treatment the mechanical properties were further optimized.XRD analysis showed that theαâ†'β-Si3N4 phase transformation increased with the porosities in the performs. Optical microscopy and scanning electron microscopy showed homogeneous microstructures. No large scale defects were observed. The aluminum alloy matrix was distributed in the strip regions and the grain sizes were very small. Stacking fault defects were existed in the Si3N4 reinforcement. No reaction between the aluminum alloy and the Si3N4 was present and the interfaces clean.Results indicated that the Vickers hardness and Youngs moduli of the materials fixed the volume fraction mix law. The tensile strength increased with reinforcement contents and then decreased after the maximum. The fracture toughness decreased with the reinforcement contents, while the bending strength and compressive strength increased with reinforcement content. The highest Vickers hardness, tensile strength, bending strength, Youngs modulus and the fracture toughness of the as-casted composites were 2.8GPa, 330MPa , 540MPa, and 11.3 MPa·m1/2, respectively. In addition, the obtained materials exhibited excellent compressive strength due to the continuous reinforcement skeleton. The compressive strength was 650MPa under 10-3S-1 compression. Aging treatment can effectively improve the strength of the composites. After aging treatment, the tensile strength was up to 434MPa, while the bending strength was up to 705MPa.The thermal expansion coefficient and thermal conductivity of the composite increased with the reinforcement contents. The thermal expansion coefficient of the composite was less than 5×10-6K-1 (room temperature), suggesting good thermal stability. High thermal conductivity of 90W·m-1·K-1 was reached.After solution at 495°C for 1h, the best aging temperature for the composites with different reinforcement contents was determined to be 175°C. The peak aging time was significantly lowered in comparison with the matrix alloy. Higher precipitate population and larger was higher precipitate sizes were present in the aluminum alloy matrix far off the Si3N4 reinforcements.
Keywords/Search Tags:porous Si3N4 preform, aluminum matrix composite, mechanical properties, aging treatment
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