Multi-scale structure and reinforcement mechanisms of multi-element composite ceramic coatings

• Multi-scale characteristics of composite ceramic coating are unveiled. • Doping of Ti, Zr, and Ce enhances the overlap of electron clouds and ionic bonding. • ZrO 2 and CeO 2 additives improves microstructure and macro mechanical properties. • The reinforcement mechanism lies in matrix densifying and crack shielding effects. Ceramic coating is of significant importance for improving metallic materials in terms of mechanical properties or durability, which is commonly encountered in the field of machinery, civil engineering, and aerospace, etc. However, ceramic materials optimization is a great challenge due to the complex multi-scale design from atomic to macro level. This paper investigates the multiscale characteristics of multi-element composite ceramic coating, including electronic properties, 3D pore structure, and engineering performances and gives their bottom-up connections, via first-principles calculations and multiscale experiments. The doping of Ti, Zr, and Ce in the alumina-based ceramic crystal improves the overlap of electronic clouds between oxygen and metal atoms, which modifies the atomic charges and enhances the ionic bonding. In terms of microstructure, it reveals the mechanisms of phase transformation toughening effect of ZrO 2 and the grain refinement and grain boundary purification effects of CeO 2 , which facilitates the amelioration of pore structure and macro mechanical properties. It provides multiscale information on the phase stability of multi-element alumina-based ceramics, shedding light on the fundamental atomic level mechanisms that play a crucial role in customizable functional designs