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 AlCoCrFeNi_2.1. 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 \(\frac{1}{2}\langle 1\overline{1 }0\rangle \) 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.