Fabrication of Al-TiB 2 Nanocomposites by Flux-Assisted Melt Stirring
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DEVELOPING high-strength, thermally stable and light materials has always attracted high interests in the materials communities for modern industrial applications. For weight sensitive aerospace and automotive applications, aluminum-based metal matrix nanocomposites containing nanoscale ceramic reinforcements (1 to 100 nm) can provide a unique solution for such applications because of high strength-to-weight ratio and thermal stability. They offer an outstanding enhancement of the mechanical and physical properties both at ambient and elevated temperatures compared with the conventional aluminum alloys.[1,2] The potential melt processes of Al-based nanocomposites need to achieve an appropriate incorporation of nano-size ceramic particles in the aluminum matrix, which is difficult due to the poor wetting of ceramic reinforcements by liquid metal.[3,4] The high clustering tendency of nanoparticles and the high oxidation susceptibility of metals and ceramics at high temperatures are the main challenges in the manufacture processes. A number of processing techniques have been employed to overcome those difficulties such as spry casting,[5] in situ synthesizing,[6–8] squeeze casting,[9,10] ultrasonic dispersion[11,12] and melt stirring.[13,14] Among the melt processing techniques, the melt stirring has prominent advantages such as simplicity of process, low manufacturing cost, proper
AHMED M. NABAWY, Post-Doctoral Fellow, and X.-GRANT CHEN, Professor, are with the Department of Applied Science, University of Que´bec at Chicoutimi, Saguenay, QC, G7H 2B1, Canada. Contact e-mail: [email protected] Manuscript submitted November 13, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
matrix-particle bonding and easy scale up for large industrial production. Strong interfacial bonding between the ceramic reinforcements and the matrix is necessary to attain a high specific modulus and a high specific strength. The strong bonding is only possible when good wetting can be achieved between ceramic reinforcements and liquid metal. Although vigorous melt stirring can improve the wetting to some extent, only some nano reinforcements are able to incorporate into the melt. The low incorporation level of ceramic substrates is mainly attributed to poor wettability and to the presence of oxides at the melt-ceramic surface. Combined of melt stirring process with an active flux wetting agent can result in a good incorporation of ceramic substrates.[15,16] The transition metal carbides, borides, and nitrides (TM ceramics) are characterized by metal-like bonding due to their uniform electron density distributions.[15–17] The metallic nature of the TM ceramics enables them to form interphase bonds with liquid aluminum without dissociation, which enhances the overall wetting and incorporation level. The TM ceramics, such as TiC, TiB2, ZrC, ZrB2, and TiN, have been incorporated successfully using a fluoride flux.[18] Thus, TiB2 nanoparticles were selected as the ceramic reinforcements for the aluminum matrix in this study. Although the feasibilit
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