Cold spray deposition of graded Al-SiC composites

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 codeposition 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.

Automated summary

This study focuses on the direct fabrication of graded composites using cold spraying technique and explores the impact of different hard-phase powder sizes on composite formation. The results indicate that well-consolidated microstructures with uniform reinforcement distribution can be achieved with fine hard-phase powder, while coarse hard-phase powder leads to less homogeneous layer build-up.