Microstructural tailoring of Cr–Mn–Mo Nitrides through Si and Y alloying

Abstract

This study investigates Si and Y alloying effects on microstructure and mechanical properties of Cr–Mn–Mo-based high- and medium-entropy nitride thin films fabricated by reactive DC magnetron sputtering, employing ab initio calculations and experimental analysis. Ab initio results show the unalloyed Cr–Mn–Mo–N system forms a stable fcc structure with negative formation energy, minimally affected by N vacancies. Alloying with Si, Y, or both further reduces formation energy, enhancing thermodynamic stability, especially at high Y concentrations. However, alloying comes with increased unit cell distortion, destabilising the crystal structure. Experiments reveal that Si and Y promote N incorporation, but complete stoichiometric metal-to-nitrogen ratios are not achieved, yielding N-vacant films. Structural analyses confirm the formation of a single-phase fcc solid solution, with lattice expansion and crystallite size refinement induced by increasing alloying concentrations. Atomic size mismatch is identified as the principal factor governing phase formation. Alloying enhances hardness without compromising elasticity, peaking at 20.5 GPa in Si-alloyed film due to nanocrystallinity, N incorporation, and strong nitride covalent bonding.