High-throughput phase exploration of ternary transition metal carbide TM-X-C (X=Al/Si) thin films

Abstract

Transition metal carbides (TMCs) are highly valued for their exceptional thermal stability (melting temperatures up to 4000 °C), refractory character, and outstanding mechanical properties, particularly hardness. These properties make TMCs crucial for applications in extreme conditions, such as in aerospace and tooling industries. Striving for novel oxidation-resistant ternary carbides, we systematically screened the phase formation of TM-X-C (where X = Al or Si) using a combined theoretical and experimental high-throughput approach. Density functional theory (DFT) calculations forecast the phase formation of (meta)stable TM-X-C solid solutions (with TM = Ti, Zr, Hf, Ta, W) using the formation energy and lattice constant ratios as structural key parameters. These theoretical predictions are experimentally validated by synthesizing over 260 compositions across the 10 different TM-X-C material systems by combinatorial magnetron sputtering. The DFT calculations indicated that Si preferentially occupies both C and TM sites, while Al tends to fill TM sites. Structural analysis experimentally confirmed the formation of face-centered-cubic TM-X-C solid solutions up to alloying contents of 25–30 at.% – for all material families except W-X-C. Additional TEM investigation confirmed the formation of fcc solid solutions. A strong correlation between prevalent phases and mechanical properties is observed, with the highest hardness values (30–40 GPa) found for fcc structured TM-X-C thin films, followed by a significant decrease entering multi-phased or amorphization phase regions – typically occurring above 25 at.% Al or Si. This comprehensive phase screening paves the way for a targeted development of novel TM-X-C ceramic thin film materials.