Mechanical properties and thermal stability of refractory metal-alloyed (Al,V)N-based high-entropy nitrides and oxynitrides

Abstract

This study explores the thermal stability and mechanical properties of (Al,V)-based high-entropy sublattice nitride (HESN) and oxynitride (HESON) coatings alloyed with various refractory metals, including Ti, Cr, Mo, W, Hf, and Zr. Through systematic annealing treatments at 800 °C, we examine the influence of alloying elements on the hardness and indentation modulus of these coatings. The results show that coatings alloyed with Ti-Hf-Cr, Ti-Hf-W, Zr-Hf-Cr, and Ti-Cr-W exhibit excellent retention of mechanical properties under prolonged thermal exposure. In particular, the Ti-Hf-W-alloyed (Al,V)N and its oxynitride variant maintain the highest hardness of ∼32 GPa during 50 h vacuum annealing at 800 °C. Conversely, the Cr-Mo-W-alloyed variants exhibit significant degradation and the formation of an Me₂N phase. X-ray diffraction analyses reveal changes in preferred crystallographic orientations and the emergence of fcc-structured domains, influencing mechanical behavior. Despite their thermal degradation, the Cr-Mo-W-alloyed (Al,V)N showed the most promising fracture toughness behavior. The findings highlight the importance of careful selection of alloying elements and compositions to optimize the performance of HESN and HESON coatings for high-temperature applications. This research provides valuable insights into the underlying mechanisms affecting the thermal and mechanical properties of advanced coatings, paving the way for future advancements in materials designed for extreme environments.