Effect of Ge addition on the microstructure, mechanical properties, and corrosion behavior of CoCrFeNi high-entropy alloys

Abstract Based on the results of many studies devoted to exploring the effect of adding different elements to CoCrFeNi alloys in the field of high-entropy alloys, in this study, Ge is included in CoCrFeNi alloys to form CoCrFeNiGex alloys (molar ratio, x = 0, 0.1, 0.2, and 0.3). Ge is used to improve mechanical properties and corrosion resistance of traditional alloys, but its application in high-entropy alloys has been less discussed. CoCrFeNiGex alloys (x ≤ 0.3) exhibit a single face-centered cubic phase. Tensile testing of these alloys revealed that the CoCrFeNiGe0.3 alloy exhibited slightly better mechanical properties—a yield strength of 223 MPa, ultimate tensile strength of 617 MPa, and elongation of 63.2%—due to solid-solution hardening. A potentiodynamic polarization test in deaerated 3.5% NaCl solution showed that Ge addition can effectively inhibit pitting corrosion and can improve the corrosion resistance of CoCrFeNi alloys by reducing the corrosion and passive current density.