Insight into deformation modes of bcc-Nb/fcc-Cantor nanomultilayer film

Abstract

The superb fracture toughness endowed by abundant deformation modes enables CrMnFeCoNi (Cantor) high-entropy alloy to be an ideal modulating layer for constructing nanomultilayer films for simultaneous strengthening and toughening. However, the lack of a comprehensive understanding of the deformation behavior of Cantor nanolayers in nanomultilayer film systems obscures the development of high-performance Cantor-based nanomultilayer films. In this work, the nanocrystalline Cantor film and bcc-Nb/fcc-Cantor nanomultilayer film were fabricated by magnetron sputtering technology, and their mechanical properties and deformation behaviors were investigated via nanoindentation and transmission electron microscopy. It is found that the plastic deformation of the nanocrystalline Cantor film is mainly carried by both grain growth and localized amorphization during indentation, which can be attributed to its intrinsically high lattice resistance and the presence of high-density grain boundaries. When the Nb nanolayers were inserted onto the Cantor nanolayers to form bcc-Nb/fcc-Cantor a nanomultilayer structure, its hardness increased to ~9.6GPa, which is 1.4 times higher than that calculated from the rule of mixture. The confinement effect of adjacent Nb nanolayers prevents grain growth in the Cantor nanolayers and promotes their complete amorphization transition in the deformed regions. However, the Cantor nanolayer on the outermost surface exhibits higher mobility, leading to the aggregation of high-density stacking faults induced by indentation. In addition, severe co-deformability occurs in the region directly below the nanoindentation tip subjected to large compressive stress, while the intermixing of Cantor and Nb nanolayers appeared in the edge region of the indentation through severe cross-slips under the combined effect of compressive and shear stresses. These results are important for understanding the deformation modes of Cantor nanolayers in nanomultilayered structure, and the findings provide new insights for developing high strength-ductility Cantor-based nanomultilayer films.