Investigation of Fracture Behavior in an Ultra-Ductile FCC Single-Crystal Alloy

Abstract

The tensile deformation behavior of a single-crystalline multi-principal alloy system was systematically investigated at room temperature along three crystallographic orientations [111], [110], and [100] to elucidate the orientation dependence of the fracture surface behavior. Previous studies demonstrated that the initial hardening response in the [100]-oriented crystal is governed by dislocation-mediated deformation. However, the tensile response in the [111]- and [110]-oriented crystals is accompanied by the progressive formation of mechanical twins and multi-slip activation. The interplay of these mechanisms results in a pronounced enhancement in strain hardening and overall plastic deformability. Moreover, the secondary or tertiary twinning activation in these orientations contributes an additional hardening stage, effectively suppressing strain localization and extending the regime of uniform plastic deformation. Scanning electron microscopy (SEM) analysis reveals an apparent paradox: while the [100]-oriented specimens, which exhibit the lowest ductility, fail via a ductile fracture mode, the more ductile [111]- and [110]-oriented crystals display features characteristic of brittle fracture. This seemingly contradictory behavior is rationalized by considering the enhanced stability against necking in the [111]- and [110]-oriented crystals, which promotes strain accumulation to higher levels and ultimately leads to brittle fracture.