Nanostructure Particle-Reinforced Transient Liquid Phase Diffusion Bonding: a Comparative Study
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THE development of aluminum–metal matrix composites (Al-MMCs) is of interest for applications in aerospace and automotive industries, owing to their high strength-to-weight ratio, formability, and corrosion resistance.[1–10] However, despite the improved properties of Al-MMCs, the lack of a reliable joining method has restricted their full potential.[11] Fusion welding is typically used to join these materials. However, joint failure generally results from defects such as particle segregation, the formation of brittle phases, weld porosity, and particle dissolution or coarsening.[1,2,4,8,11] Transient liquid phase (TLP) diffusion bonding provides an alternative to fusion welding and has been extensively studied for joining particle-reinforced AlMMCs.[1,11] In this process, a thin continuous layer of liquid is formed at the joint interface, which wets the contacting metallic substrates.[12–16] The advantage of using this process is that reinforcing particles are incorporated into the bond region either by using a particle-reinforced insert layer[19] or by the melt-back of the substrate metal occurring as a result of the eutectic reaction between the interlayer and the aluminum alloy.[17] It has been shown in the scientific literature that melt-back can be controlled by using thin interlayer KAVIAN O. COOKE, Postdoctoral Candidate, and TAHIR I. KHAN, Professor of Materials Engineering, are with the Department of Mechanical and Manufacturing, University of Calgary, Calgary, AB, Canada T2N 1N4. Contact e-mail: [email protected] GOSSETT D. OLIVER, Professor of Mechanical Engineering, is with the Department of Mechanical Engineering, University of Technology, Jamaica, 237 Old Hope Road, Kingston 6, Jamaica W.I. Manuscript submitted September 11, 2010. Article published online March 22, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
materials. It has also been suggested that heating rate, interlayer composition, and thickness are most important in reducing melt-back during TLP bonding. These parameters also determine the width of the liquid phase, removal of surface oxide film, and particulate redistribution in the bonded region.[16] A long heating stage will result in the diffusion of more solute (MPD) into the base material. However, if the heating stage is too long because the heating rate is too slow, the maximum composition of solute in the interlayer may dip below the solidus composition at the bonding temperature (Tb) and no liquid will form at the bonding temperature.[16] This problem will be most severe with very thin interlayers and low solute concentrations. Metal interlayers in the shape of foils, such as Cu, Zn, Ni, and Ag,[18,19] are often used in the joining process. Unfortunately, the use of metal foils to join particlereinforced composites can result in the formation of dispersion-free zones (DFZs) within the joint zone. Recent studies into joining AL-MMCs focused on using soldering or brazing, since these techniques avoid the problems associated with fusion and may offer improved flexibility in
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