Tailoring the Microstructure and High‐Temperature Stability of <scp>CoNiV MEAs</scp> Through Chromium Alloying

Abstract

ABSTRACT The performance and longevity of machines, infrastructure, power plants, and structural components depend heavily on materials with high strength and damage tolerance. However, corrosion and high‐temperature oxidation progressively degrade these properties, often leading to premature failure. Medium‐entropy alloys (MEAs), a subclass of high‐entropy alloys, are characterized by their compositional complexity and high configurational entropy, which can give rise to unique combinations of mechanical and chemical properties. This study investigates the influence of chromium (Cr) additions (5 wt.%, 10 wt.%, and 15 wt.%) on the mechanical behavior, oxidation resistance, and phase stability of CoNiV MEAs at elevated temperatures. Nanoindentation testing revealed a clear improvement in mechanical performance with increasing Cr content, with the 15 wt.% Cr alloy exhibiting the highest hardness (912.84 Hv), lowest indentation depth (1451.53 nm), and highest elastic modulus (256.77 GPa). Corrosion testing in 0.5 M H 2 SO 4 and 3.5 wt.% NaCl solutions showed that the 15 wt.% Cr alloy also had the lowest corrosion current density and corrosion rate, confirming superior electrochemical stability. Furthermore, oxidation and hot corrosion tests conducted at 800°C in a 50:50 Na 2 SO 4 –NaCl environment demonstrated that the 15 wt.% Cr alloy had the lowest mass gain, indicating the formation of a stable and protective Cr 2 O 3 oxide layer. These improvements are attributed to microstructural refinement, solid solution strengthening, and the formation of a dense, adherent oxide scale. Overall, the findings highlight the potential of Cr‐doped CoNiV MEAs particularly with 10–15 wt.% Cr as strong candidates for high‐temperature applications requiring enhanced mechanical integrity and oxidation resistance.