Strength and plasticity of Cr/Cr <i> _X </i> N multilayers with gradient nanoarchitectures

Refining grain size and enhancing thermally assisted grain boundary activation are fundamental strategies for improving the plasticity of high-strength ceramic materials. In this study, Cr/CrXN gradient multilayers with finer ceramic grains were synthesized by modulating the nitrogen flow rate in reactive sputtering with continuous gradients. Compared to conventional Cr/CrN multilayer that exhibit shear instability, the Cr/CrXN gradient multilayer achieved a yield strength/flow strength of 6.7 GPa/6.9 GPa with the yield strength increased by 21.8% and a large plastic strain of 5.8% with improved by 50% at 200°C, and exhibit a superb strain hardening capability over 10% uniform strain at 400°C. Microscopy characterizations revealed that high grain boundary volume is critical for the enhanced plasticity of Cr/CrXN gradient multilayer because of grain boundary sliding and grain rotation, while the geometric constraints of neighboring grains contribute to continuous hardening during deformation.