Synthesis and characterization of ceramic high entropy carbide thin films from the Cr-Hf-Mo-Ta-W refractory metal system

Abstract

We use reactive DC magnetron sputtering to showcase synthesis strategies for multicomponent carbides with the NaCl-type fcc structure and illustrate how deposition conditions allow controlling the formation of metallic and ceramic single phases in the Cr-Hf-Mo-Ta-W system. The synthesis is performed in argon flow and different acetylene flows from 0 to 12sccm, at ambient and elevated temperatures (700 °C), respectively, hindering/promoting the adatom diffusion. Structural and microstructural investigations reveal the formation of the bcc metallic phase (a=3.188−3.209Å) in films deposited without acetylene flow, also supported by ab initio density function theory (DFT) analysis of lattice parameters as a function of the C content. Experimentally, a bcc-to-fcc phase transition is observed through the formation of an amorphous coating. Contrarily, samples deposited in higher acetylene flow show an fcc multielement carbide phase (a=4.33−4.49 Å). The crystalline films reveal columnar morphology, while the amorphous ones are very dense. We report promising mechanical properties, with hardness up to 25±1GPa. The indentation moduli reach up to 319±6GPa and show trends consistent with DFT predictions. Our study paves the path towards the preparation of Cr-Hf-Mo-Ta-W multicomponent carbides by magnetron sputtering, showing promising microstructure as well as mechanical properties.