Characterization of a diffusion-bonded Al-Mg alloy/SiC interface by high resolution and analytical electron microscopy
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INTRODUCTION
THE bonding of metals to ceramics is of fundamental interest, since the properties of numerous advanced material systems depend strongly on bonding at metal/ ceramic interfaces. Unfortunately, many ceramics are not readily wet by commonly used metals, resulting in low bond strength. {~'2j Addition of reactive elements to the metal has been shown to improve the metal/ceramic wettabilitytL3} by either (1) reducing the metal/ceramic interface energy or (2) reacting with the ceramic to form interfacial reaction products. The formation of interfacial reaction products can improve the metal/ceramic bond strength if the reaction product has favorable characteristics, such as limited thickness14}and an orientation relationship with the ceramic, tS} In a recent article, t6} the structure of a pure A1/SiC interface fabricated in the presence of oxygen (from the residual oxides A1203 and SiO2 present on the A1 and SiC surfaces, respectively) was examined. Transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) indicated that a glassy phase containing A1, Si, C, and O formed at this interface by a solid-state reaction (SSR). In this article, the effect of Mg addition (to A1) on this interfacial structure is examined and the observed interfacial structure is contrasted with that at the AI/SiC interface. Several previous studies have investigated the interfacial and precipitation reactions in Mg-containing A1 alloys reinforced with as-received [7-~] or oxidized SiC particles, t7,8] Oxidized SiC panicles typically have a 40 to 50-nm-thick layer of SiO2 on the surface, while asreceived SiC particles have a 4 to 5 nm oxide layer on the surface. Ribes et al.[8] did not observe the formation of any interfacial reaction products at a 6061-Al/asreceived SiC particle interface but observed the formation of A12MgO4 at a 6061-A1/oxidized SiC particle interface. Wang et a/. I91 reported the formation of P.L. RATNAPARKHI, Graduate Research Assistant, and J.M. HOWE, Associate Professor, are with the Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903. Manuscript submitted January 8, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
A12MgO4 at the interlace in a cast SiC-particulate reinforced AI(A356)/SiC composite. In contrast, Henriksen t~~ reported the formation of MgO at the interface in a SiC whisker-reinforced AI alloy fabricated by the squeeze-casting technique. Formation of MgO at the 2124 Al-alloy/SiCw interface was also observed by Nutt and Carpenter. j~j} Formation of AI2MgO4 and MgO at a 6061 Al-alloy/Si3N4 interface in a squeeze-cast composite has also been reported, l~zl In all of these studies, the composites were processed in the liquid state and formation of the oxides AIzMgO4 or MgO involved a reaction between the alloy and the SiOz layer present on the SiC surface. In the present investigation, the A1-Mg/ SiC interface was fabricated by solid-state joining. Besides interfacial reaction products, it is important to consider the various Al-
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