Preparation of a Nano-Laminated Sc2SnC MAX Phase Coating on SiC Fibers via the Molten Salt Method

TL;DR

A new method to coat SiC fibers with a nano-laminated Sc2SnC MAX phase is developed, improving composite properties under high temperatures.

Contribution

A novel molten salt method is introduced to synthesize Sc2SnC coatings on SiC fibers with controlled morphology.

Findings

Sc2SnC coatings with hexagonal flake-like morphology were successfully synthesized on SiC fibers.

The ScCx intermediate layer was identified as critical for the coating's formation.

Element diffusion and defect formation influenced the coating's grain structure and growth orientation.

Abstract

The incorporation of MAX phase interface layers into silicon carbide (SiC) composites has been shown to significantly enhance mechanical properties, particularly under irradiation conditions. However, conventional Ti-based MAX phases suffer from thermal instability and tend to decompose at high temperatures. In this work, an Sc2SnC coating was successfully synthesized onto the surface of SiC fibers (SiCf) via an in situ reaction between metals and pyrolytic carbon (PyC) in a molten salt environment. The PyC layer, pre-deposited by chemical vapor deposition (CVD), served as both a carbon source and a structural template. Characterization by SEM, XRD, and Raman spectroscopy confirmed the formation of Sc2SnC coatings with a distinctive hexagonal flake-like morphology, accompanied by an internal ScCx intermediate layer. By turning the Sc-to-Sn ratio in the molten salt, coatings with varied morphologies were achieved. ScCx was identified as a critical intermediate phase in the synthesis process. The formation of numerous defects during the reaction enhanced element diffusion, resulting in preferential growth orientations and diverse grain structures in the Sc2SnC coating.

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