Improvement of Wear Resistance in Alumina Matrix Composites Reinforced with Carbon Nanotubes
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CARBON nanotubes (CNTs) have been considered as new advanced materials with great potential, because they have excellent mechanical, chemical, thermal, and electrical properties as well as nanosize characteristics.[1–3] Because CNTs also have a low density (approximately 2 g/cm3) and a high elastic modulus (approximately 1.8 TPa), they can be favorably used as reinforcements for nanocomposites.[4] When they are added to polymer, metal, and ceramic matrix composites,[5–10] the electrical and mechanical properties of the CNT-reinforced composites can be improved. In particular, the addition of CNTs to ceramic matrix composites has been conducted to improve fracture toughness, which is the most important property of ceramics.[11] SUNG WAN KIM, Graduate Student, and WON SUB CHUNG, Professor, are with the Department of Materials Science and Engineering, Pusan National University, Pusan, 609-735, Korea. KEE-SUN SOHN, Associate Professor, is with the Department of Materials Science and Metallurgical Engineering, Sunchon National University, Sunchon, 540-742, Korea. CHANG-YOUNG SON, Research Assistant, is with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784, Korea. SUNGHAK LEE, Professor, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, is also with the Department of Materials Science and Engineering, Pohang University of Science and Technology. Contact e-mail: [email protected] Manuscript submitted May 7, 2009. Article published online December 18, 2009 380—VOLUME 41A, FEBRUARY 2010
According to the report by Siegel et al.,[12] when 10 vol pct of CNTs was added into the alumina matrix, the fracture toughness increased by 24 pct over the monolithic alumina. Peigney et al.[13] reported that the fracture toughness and flexure strength of CNT/Fe/ Al2O3 composites fabricated by hot pressing were lower than those of a CNT-free Fe/Al2O3 composite, although CNTs were well distributed in the matrix. These reports indicate that difficulties related to the composite fabrication pose problems in improving properties and that various microstructural factors seriously affect the properties. In addition, there are quite a few reports on alumina matrix composites reinforced with CNTs involving difficulties related to fabrication, and only limited information is available on the wear resistance of the composites. The wear process of alumina matrix composites reinforced with CNTs is a complex one, and is integrally affected by various factors such as abrasive wear, delamination wear, intergranular cracking, and wear by the falloff of alumina.[9,14–17] Wear involves microscopic and dynamic processes occurring in the interface between the composite and the counterpart material, and is almost impossible to observe directly. Interpretation is also difficult because kinetic, thermal, and material factors are intricately in interaction. Depending on the wear modes, e.g., abrasive wear or delamination wear, CNTs and the matrix holding the CNTs can play M
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