Bidirectional Regulation of Tantalum Content on High‐Temperature Oxidation and Chloride Corrosion Resistance of CoCrFeNi High‐Entropy Alloys

ABSTRACT

To address the trade‐off between high‐temperature oxidation resistance and chloride corrosion resistance of CoCrFeNi high‐entropy alloys (HEAs), CoCrFeNiTa _x ( x  = 0.5, 1.0, 1.5, 2.0) alloys were fabricated via vacuum hot‐pressing sintering. The bidirectional regulation of Ta content on oxidation at 800°C and corrosion in 3.5 wt% NaCl solution was systematically investigated. Increasing Ta degrades oxidation resistance with higher mass gain, parabolic rate constant K _p , and thicker oxide layers, owing to the deteriorated oxide structure, diluted Cr‐based protective film, and accelerated ionic diffusion through the Laves phase. Conversely, Ta markedly improves corrosion resistance by raising the corrosion potential and reducing the corrosion current density, due to the formation of a dense Ta ₂ O ₅ passive film, which repairs structural defects and resists the attack of chloride ions. This work clarifies the underlying bidirectional regulation mechanisms and provides guidance for the composition design of HEAs applied in extreme environments.