Research on new technologies in the field of advanced materials have contributed to the development of high-entropy alloys (HEAs), a relatively new family of multicomponent alloys composed of at least five alloying elements with an atomic composition of 5-35 % each by offering a configurational entropy of mixing ΔS_conf of at least 1.5R, where R is the gas constant. The incorporation of a larger number of elements with high concentrations leads to new material properties by changing physical and metallurgical aspects that offer superior magnetic, mechanical, and electrochemical characteristics.

Literature data indicate that the oxidation resistance of eight HEAs in the CoCrFeMnNi family was studied by monitoring mass change oxidation kinetics at 650°C and 750°C for 1100 hours in comparison with the performance of commercially available alloys, nickel-based superalloy 230 (N06230) and austenitic stainless steel 304H (S30409) [1]. Results from this investigation revealed greater oxidation resistance from some multicomponent alloys compared to 230 and 304H alloys; and it is influenced by HEAs Cr or Mn compositional dependence, gaining valuable knowledge for their future use in commercial applications.

The purpose of this research was to evaluate the corrosion behavior of these advanced materials under aqueous acidic conditions by exposing the multicomponent alloys to immersion testing, and study their electrochemical kinetics versus the corrosion performance of Hastelloy® C276 (UNS N10276) and stainless steel 316L (UNS 31600). The HEAs selected are considered for corrosion protection applications of natural gas transmission pipelines. Weight loss analysis revealed the corrosion rates of these materials while changes on the metal surface were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Potentiodynamic polarization curves elucidated active, active-passive, and passive regions of these alloys to determine the presence of localized corrosion. Experiments were carried out under deaerated aqueous conditions of 3.5 wt.% NaCl solutions at pH 4 and temperature of 40°C. Oxygen content is suppressed from the environment by using CO₂ as stripping gas.

Reference: G.R. Holcomb, J. Tylczak and C. Casey, JOM, 67 (2015) 2326-2339