Phase formation and thermal stability of quaternary MAX phase thin films in the Cr-V-C-Al system: an experimental combinatorial study

Mn+1AXn phases are atomically layered ternary carbide and nitride compounds that possess remarkable and unusual combination of properties. Tailoring of individual atomic layers via alloying to synthesize quaternary MAX phases is attracting unprecedented interest with the discovery of new solid solution and ordered phases.
Nowadays, there is tremendous interest in MAX phase thin films for applications in surface engineering. Intensive efforts are ongoing to explore new approaches for high-quality (i.e. single-phase and textured) ternary thin films, while the synthesis of quaternary thin film materials has been rarely explored yet. In this study, we focus on the growth of (CrxV1-x)2AlC quaternary thin films and study their formation, microstructure, and thermal stability. CrV/C/Al multilayers with pre-defined nanostructured architectures (i.e. periodical stacking of nanolayers and variation of the Cr:V ratio) were deposited by combinatorial experiments in magnetron sputtering using a specific segmented Cr-V, and pure graphite, and Al targets. These multilayer precursors were synthesized without substrate heating, and post-annealed from 300°C to 1000°C in vacuum to investigate their temperature-dependent phase formation. ... mehrFor this purpose, and to identify the underlying reaction mechanisms for potential MAX phase formation, in-situ HTXRD analyses were carried out. The composition and microstructure of the films before and after annealing were systematically studied, including methods with both global and local resolution (EPMA, TEM, APT, etc). Crystallization of solid solution (CrV)2AlC MAX phases above 600°C was confirmed for all multilayer precursors, i.e. for all different compositions and Cr:V ratios. The quaternary MAX phase thin film structures tend to decompose when vacuum annealed at 1200°C for more than one hour. We will discuss how the preferential diffusion behavior triggers the complex quaternary MAX phase structure formation and explore the correlation of their synthesis, microstructure, and properties from the nanostructured multilayer precursors.