Cyclic plasticity of high entropy alloy: experiments, modelling and simulations

Prof. Xu Zhang

School of Mechanics and Engineering, Southwest Jiaotong University, Chengdu, PR China

21. January 2019, 17.00
WW8, Raum 2.018, Dr.-Mack-Str. 77, Fürth

High entropy alloys (HEAs), which are composed of at least three principal elements, have innovated the design strategy of metal materials from the perspective of thermodynamic “entropy”. Thus, they are expected to have a variety of excellent mechanical properties, such as great strength, high elongation and fatigue. During the service life, alloys are usually subjected to cyclic loading, especially stress loads. Therefore, it is important to investigate their cyclic deformation behavior and establish a cyclic constitutive model to predict their service ability, based on revealing the intrinsic plastic deformation mechanisms. However, at present experiments and constitutive models regarding the cyclic deformation behavior of HEAs are still insufficient. The present paper focuses on the non-equiatomic single-phase interstitial high entropy alloy (iHEA) Fe49.5Mn30Co10Cr10C0.5, and conduct the stress-controlled cyclic tests under different stress levels. The stress-strain responses show that the iHEA has significant Bauschinger effect and ratcheting behavior. Using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI), it was observed that multiple deformation twinning and massive martensite transformation are activated in iHEA during cyclic deformation, besides dislocation glide. Based on experimental observations, we develop a micro-mechanism based cyclic constitutive model, and perform the crystal plasticity finite element method (CPFEM) simulations, according to the loading conditions in experiments. The simulated results indicate that this constitutive model can describe the ratcheting behavior of iHEA well. Furthermore, the evolution of microstructures, such as dislocation density, volume fractions of twin and martensite with increasing number of cycles are discussed. The evolution of martensitic distribution in the represent volume element (RVE) are also analyzed.