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/Cr<i>_X</i>N 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/Cr<i>_X</i>N 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/Cr<i>_X</i>N gradient multilayer because of grain boundary sliding and grain rotation, while the geometric constraints of neighboring grains contribute to continuous hardening during deformation.细化晶粒尺寸、强化热辅助晶界活化是提升高强度陶瓷材料塑性的核心策略。本研究通过在连续梯度反应磁控溅射工艺中调控氮气流量，合成了拥有更精细陶瓷晶粒的Cr/CrₓN梯度多层膜。相较于表现出剪切不稳定性的传统Cr/CrN多层膜，Cr/CrₓN梯度多层膜在200℃下实现了6.7 GPa/6.9 GPa的屈服强度/流动强度，屈服强度提升21.8%，塑性应变达5.8%（增幅达50%），并在400℃下展现出优异的应变硬化能力，可实现10%以上的均匀应变。显微表征结果表明，由于晶界滑移与晶粒转动效应，高晶界体积占比对Cr/CrₓN梯度多层膜的塑性提升至关重要；而相邻晶粒的几何约束效应则在变形过程中促进了持续硬化。