Basal planar fault formation in a chemically complex Laves phase containing eutectic high entropy alloy

Abstract

Basal planar defects formed in a C14-type Laves phase containing eutectic high-entropy alloy were investigated using aberration-corrected transmission electron microscopy. After quasi-static deformation at 800 °C different basal planar defects were observed. Through exploring the dislocation cores, these planar faults are believed to form via synchroshear mechanism. However, at 800 °C with a much higher strain rate, only dislocation activities were observed, which indicates that synchroshear is a thermally activated process. Through site occupancy analysis, Ta occupies 4f sites, Co, Ni and Fe occupy 2a and 6h sites, while Cr prefers 2a sites which can facilitate synchroshear owing to reduced atomic bonding inside triple layers. Due to insufficient Ta fraction anti-sites and vacancies exist in the C14 lattice. By theoretical calculation the substitution of Ta by Cr can reduce the energy barrier for synchroshear. Thus, all these contributions promote stacking fault formation at low temperatures in chemically complex Laves phases.