Analysis of phase transformation and deformation behaviors on Laves phase of as-cast (CoCuFeNi)100-xZrx high entropy alloys

Abstract

In this study, the effects of Zr contents on the microstructure, phase, mechanical properties and deformation behavior of CoCuFeNi medium entropy alloy (MEA) have been investigated. With increasing Zr contents to 7 at%, Ni-Zr C14 type Laves phase formed due to high negative mixing enthalpy between Ni and Zr contents which display eutectic morphologies in matrix. The mechanical properties increased from 232 MPa to 446 MPa without decreasing plastic strain. Furthermore, the enhanced work-hardening rate was observed according to adding Zr. By the TEM analysis, we can confirm that the observed deformation behavior is relative to the phase transformation of Laves phase, in which C14 type Laves phase transformed into C15 type Laves phase through synchroshear process. Numerous dislocation formed in FCC phase piled up in C14 Laves/FCC interface, which made the enhanced hardenability. On the other hand, the transformed C15 Laves showing better dislocation mobility enable dislocation to glide into C15 Laves/FCC interface, which allowed the stress-strain curve to change the slope. In this study, our research provides the detailed transformation mechanism and deformation behavior in terms of dislocation motion.