New Quaternary MAX Phase Thin Films: Understanding the Thermally Induced Microstructural Evolutions and Reaction Mechanisms in Nanostructured Multilayers via Experimental Combinatorial Study

• Applicant: Dr.-Ing. Chongchong Tang, Ph.D.
• Subject Area: Synthesis and Properties of Functional Materials
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 464878149

MAX phase materials (Mn+1AXn, M = transition metal, A = A group element, X = carbon or nitrogen, n =1, 2, 3) are atomically layered compounds that possess unique properties combining attributes of both metals and ceramics. Multi-elemental alloying of individual atomic layers is a powerful tool to synthesize novel quaternary MAX phases and offers manifold opportunities to widely tune their properties through tailoring their local chemistry and structural complexity. Recently, apart from random solid solution structures, new chemically ordered quaternary (M′M″)n+1AXn structures on M layers have been discovered, including out-of-plane ordering (referred to as o-MAX) and in-plane ordering (referred to as i-MAX). However, the synthesis of such bulk quaternary MAX phases in single-phase structure remains a great challenge. Thin-film synthesis of quaternary MAX phase materials is an emerging research field in materials science, and, chemically ordered quaternary MAX phase thin films have not been reported yet. In this proposal, we aim to synthesize single-phase and, potentially, basal-plane textured quaternary (M′M″)n+1AXn thin film materials in three quaternary model systems (Cr-M″-Al-C with M″: V, Ti, Zr). This will be achieved by transformation of nanoscale elemental multilayers with pre-defined nanostructured architectures (“thin film precursors”) through appropriate treatment processes, utilizing an experimental combinatorial approach for the thin film precursor design and synthesis. The research work will target at first the synthesis of quaternary random solid solution MAX phases, and will then address the synthesis of the two complex ordered structures. The scientific objectives of this proposal are: 1) to understand the microstructural evolutions and their underlying reaction mechanisms during thermal processing of the nanostructured multilayers towards the formation of different quaternary MAX phase thin films, and, 2) to explore the composition–microstructure–properties relationship of the quaternary MAX phase thin films. The thermal processing of the thin film precursors will cover annealing experiments at various heating rates and kinetics (i.e. very low as well as fast heating rates), including selected experiments with a novel thin film calorimeter. The scientific work will be based on intensive thin film characterization methods with atomic-scale resolution. Thus, the proposed research will contribute to developing suitable thin film precursor architectures and thermal treatment processes for the synthesis of phase-pure quaternary MAX phase thin films. The scientific outcome will lead to an understanding of the role of local chemistry (composition and chemical ordering) and microstructure on the properties of such new MAX phase thin film materials.

• DFG Programme: Research Grants