Microstructure, mechanical properties and corrosion resistance of CoCrFeNiWx (x=0, 0.2, 0.5) high entropy alloys

In this study, the microstructures, microhardness, compression performance and corrosion resistance of CoCrFeNiWx (x = 0, 0.2, 0.5, denoted as W-free, W-0.2, and W-0.5, respectively) high-entropy alloys (HEAs) have been studied. Intensive studies show that W addition leads the severe lattice distortion, and thus aggravates the driving force of composition decomposition for W-free HEA. The dual-phase with face-centered cubic (FCC) microstructure in W-0.2 and W-0.5 HEAs was identified. In addition, a mu-(FeCoCr)(7)W-6 phase precipitate from the matrix in W-0.5 HEA. Moreover, the 11.12 at.% W addition induces the formation of cell dendrites and eutectic inter-dendrites with fine laminar spacing in W-0.5 HEA. W addition obviously decreases the grain size, and enhances the microhardness and yield strength of W-free HEA. The W-0.5 HEA has the high microhardness of 357.9 HV and yield strength of 556 MPa, while maintaining the reasonable fracture strain of 35.6%. The strengthening mechanism of mechanical properties can be attributed to the grain refinement strengthening, solid-solution strengthening, and interface hardening. The enhancements of the latter two strengthening effects depend upon the existence of dual FCC phases. The pitting resistance of the containing-W HEAs is enhanced in seawater solution compared with W-free HEA. Especially, the W-0.5 HEA bears the best pitting resistance and easy passivation behavior, owing to that W addition improves the stability of the protective layer.