Gradient TiZrHfMoW/(Mo,W)N multilayer coatings formed via Mo/W segregation: Coherent interface architecture and toughening mechanisms

Inspired by the hierarchical architectures found in natural materials, a TiZrHfMoW/(Mo,W)N gradient multilayer coating was fabricated using a simple one-step sputtering deposition technique, leveraging segregation-induced self-assembly rather than conventional sequential deposition. During the deposition process, the spontaneous segregation of W and Mo led to the formation of a layered (Mo,W)N phase within the TiZrHfMoW matrix. These sublayers exhibit epitaxial relationships with the surrounding high-entropy alloy phase, forming well-defined coherent interfaces. Compared to a monolithic (Mo,W)N coating, the gradient multilayer system maintains comparable surface hardness (∼18.8 GPa) while significantly enhancing damage tolerance under mechanical loading. The synergistic toughening mechanisms include solid solution strengthening, interface coherency strain, grain boundary hardening, and a spatially varying modulus that aids crack arrest and stress distribution. This work demonstrates a scalable, self-organizing design strategy for architectured coatings with offering superior mechanical performance under demanding service conditions.