Thermal properties of kinetic spray Al-SiC metal-matrix composite
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Kinetic spray deposition provides a new means for producing composite materials with tailored physical properties. We report on measurements of the thermal conductivity and thermal-expansion coefficient for several compositional variations of kinetically sprayed Al–SiC metal-matrix composites. As a result of the deposition process, inclusion of SiC particles saturates in the 30–40% volume fraction range.
I. INTRODUCTION
Metal-matrix composites (MMCs) are a class of materials developed to achieve physical properties that are more attractive than those of the constituents. Applications may range from structural components (low density, high strength) to electronic packaging (low thermal expansion, high thermal conductivity). The tailoring of specific physical properties is achieved by incorporating a controlled amount of ceramic filler particles within a metal matrix, and a number of material combinations have been produced and documented in the literature.1 One popular MMC is the material combination of Al and SiC particles. This system has the potential for lowdensity structural components2 as well as a low thermal expansion component in electronic packaging applications.3,4 A number of processing schemes for producing MMC materials have been demonstrated with varying degrees of success in terms of composite properties and incorporation of filler particles.1 One particularly successful scheme involves hot pressing of cold-mixed constituent Al and SiC filler particles.2 This process has been well documented, and the physical properties for a large range of SiC content measured. In the following, we report on measurements of thermal conductivity and thermal-expansion coefficients for Al–SiC composites fabricated by kinetic spray deposition of feed powders with a systematic variation of the filler particle volume fraction. II. MMC PREPARATION
Composite samples were fabricated by kinetic spray deposition of mixtures of Al and SiC powders. This process uses a high-pressure gas to accelerate powder particles that impinge on a substrate in solid form at temperatures well below the powder melting point. As a result, coatings (or thick deposits) with low porosity, low J. Mater. Res., Vol. 18, No. 4, April 2003
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oxide, and low residual stress are formed. Using an air carrier gas at 370 °C we measure particle velocities on the order of 400–500 m/s at 5 mm from the nozzle exit.5 Multiple passes of the substrate under the spray gun produces deposits approximately 1 cm thick, with mass deposition rates on the order of 43 g/min. Details of our deposition apparatus and procedure are documented in Ref. 5. The feed powder compositions in terms of volume fraction percentages are listed in Table I. The aluminum matrix powder is composed of pure Al particles 51– 63 m in diameter. As indicated, both the volume fraction and the size of SiC filler particles were systematically varied to explore as much of the thermal property space as possible. The SiC particles were derived from h
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