Hardening an amorphous-crystal dual-phase Ni–Mo–W alloy with atomic-scale planar faults

Amorphous-crystal dual-phase nanostructures represent a highly promising architectural paradigm for achieving exceptional mechanical properties. However, strategies to design such high-strength materials remain an unresolved challenge. Inspired by thermally-triggered grain boundary relaxation in nanograined alloys, we introduce an innovative approach to incorporate an ultrahigh density of atomic-scale planar faults, including stacking faults and twins, into nanocrystals in an amorphous-crystal dual-phase nanostructure realized via in-situ primary crystallization in a concentrated amorphous Ni-26.6 at.% Mo-3.5 at.% W alloy. The atomic-scale planar faults render tetragonal-shaped nanocrystals and substantially enhance the microhardness of the dual-phase alloy. The observed hardening is closely related to the density of planar faults determined by crystallization temperature. Furthermore, these planar faults markedly elevate the Young's modulus of the nanocrystals. The increased elastic modulus enhances the nanocrystals' ability to arrest shear bands and encourage shear band multiplication through the activity of partial dislocations. The underlying mechanism of hardening can be attributed to the stabilization of confined interfaces as well as enhanced elastic modulus to shear band multiplication. This study provides a novel pathway for optimizing the mechanical performance of dual-phase nanostructured alloys through atomic-scale defect engineering.