Cold spray deposition of graded Al-SiC composites

Abstract

Continuously graded materials of Al-based matrix composites reinforced by SiC particles attract increasing attention due to demands for altered thermoelectric and mechanical properties over defined scales. To ensure tailored gradients while avoiding undesirable side reactions, this work focusses on cold spraying as a promising production technique. So far, cold spraying has proved the potential for fabricating aluminum matrix composites with a uniform distribution of reinforcements. The present study explores the direct fabrication of graded composites by applying a constant feed rate of Al powder and gradually increasing feed rates of SiC powder during cold spraying by employing two powder feed lines. The systematic comparison of two SiC powder sizes allows for the identification of common features in composite formation and deducing technical prerequisites for obtaining uniform as well as graded composites. Key issues of microstructural and mechanical investigations concern the attainable hard-phase contents and distributions over the deposit thickness. If a fine hard-phase feedstock powder is used, well-consolidated microstructures with graded SiC distributions are obtained. In case of a coarse hard-phase powder, the layer build-up is less homogeneous. The comparison between the results of the present work and the corresponding literature data reveals similar deposition efficiencies of SiC for co-deposition and the use of pre-mixed powders. However, if cold spraying such blends, the hard-phase contents of the deposits are lower than those of the feedstock powder mix. Furthermore, hard phase contents are lower than for conventional, high-temperature processing techniques. Based on the comparison, the requirements for achieving a wider range of hard phase contents in cold sprayed deposits are elucidated, in particular regarding the feedstock powders and the powder feeder. The acquired understanding can also be transferred to cold spraying of other graded material combinations. In comparison to conventional, high-temperature processing techniques, dual powder feeder-based cold spraying is a promising alternative to manufacture graded composites. By adjusting individual powder feed rates, it allows for the deposition of various mixtures to yield functionally graded structures over the deposit buildup. • Functionally graded Al-SiC composite is deposited by cold spray using two powder feed lines. • Two SiC powder sizes allow comparison in composite formation and technical pre-requisites. • This work reveals similar deposition efficiencies of SiC for co-deposition with pre-mixed powder. • Typical methods of fabricating graded Al-SiC materials were compared with cold spray. • The attained understanding can be transferred to tune deposition of other graded materials.