Mechanism Controlling Elevated Temperature Deformation in Additively Manufactured Eutectic High-Entropy Alloy

In the present study, high-temperature deformation behavior and creep response have been investigated for an additively manufactured eutectic high-entropy alloy (AM EHEA) with the composition AlCoCrFeNi2.1. The microstructure revealed L12 and bcc phases. High-temperature compression studies show that the yield strength tends to increase with the increase in temperature up to 400 °C and then starts declining till 800 °C. The yield strength was found to be almost similar at room temperature and 600 °C. To understand the anomaly in the temperature dependence of yield strength, first-principles density functional theory (DFT) calculations were performed using the diffuse multi-layer fault model (DMLF) to estimate the planar fault energies associated with the L12 crystal structure. It has been observed that the planar fault energy (PFE) associated with Antiphase boundary energy APB {001} was found to be the minimum among APB {111}, Superlattice intrinsic stacking fault SISF {111}, and Complex stacking fault CSF {111} thereby favoring the cross slip event of 12⟨11¯0⟩\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\frac{1}{2}\langle 1\overline{1 }0\rangle $$\end{document} from {111} to {001} leading to Kear-Wilsdorf (KW) lock. Yield strength anomaly can be attributed to the presence of L12-ordered intermetallic phase, where thermal activation of secondary slip systems plays a significant role during deformation. Further, a time-dependent deformation study at different constant loads was performed at an elevated temperature where the anomaly was observed. It was revealed that a sequential creep mechanism with dislocation climb-controlled creep is the dominant mechanism rather than diffusion creep.