奥氏体不锈钢过饱和渗氮层微纳多级结构及表面复合改性机制

The nitrogen-supersaturated (10-35 at.%) layer on austenitic stainless steel produced by low-temperature nitriding has remarkable compound performance of wear and corrosion resistance. However, it is relatively difficult to model and illustrate the combining modification mechanism since the nitriding layer is metastable phase with heterogeneous structure. In this project, a micro-nano hierarchical structure of this layer is proposed. The structures at the first level are micron-scale clustered stacking faults and the face-centered cubic matrix alternatively distributed in the layer. The structures at the second level are nano-scale heterogeneous short-range ordered structures, which are composed of atomic clusters (Fe,Ni,Cr)6N. The plasma source ion nitriding process with an independent intellectual property rights is utilized to modify austenite stainless steel. The composition and structure of the clustered stacking faults and the heterogeneous short-range ordered structures will be analyzed by a combination of electron microscopy techniques, including electron diffraction and electron energy-loss spectroscopy, and first principles calculations. The micro-nano hierarchical structure model will be established. The formation of hierarchical structure and the effects of temperature, alloy elements and stress filed will be explored. Furthermore, the relationship between nitrogen concentration, clustered stacking faults, short-range ordered structures and the compound performance of wear and corrosion resistance will be established. Then, the roles of the hierarchical structure on the compound modification mechanism will be illustrated. The results will enrich and develop the theories of formation and stabilization of metastable phase on alloyed surface. They will also provide theoretical basis for the optimization and development of the low-temperature plasma nitriding process with high quality, high stability and high efficiency.

奥氏体不锈钢低温渗氮形成氮超高过饱和（10-35at.%）改性层，具有优异的耐磨损抗腐蚀复合性能。针对渗氮层是非均匀亚稳单相结构，难以建模并阐明耐磨抗蚀复合改性机制的难题，本项目提出渗氮层具有微纳多级结构，一级结构为微米尺度的层错簇和FCC基体，二级结构为八面体团簇(Fe,Ni,Cr)6N组合形成的纳米非均匀短程有序结构。采用自主知识产权的等离子体源离子渗氮技术改性处理奥氏体不锈钢，将电子衍射、电子能量损失谱等电子显微学方法与第一性原理计算紧密结合，实现对层错簇和短程有序结构的成分和结构分析，建立微纳多级结构模型，阐明温度、合金元素和应力场作用下多级结构形成规律。进而建立氮浓度、层错簇和短程有序结构与耐磨抗蚀性能的内在科学关联，揭示多级结构对耐磨抗蚀复合性能的作用机制。研究结果将丰富和发展合金化表面亚稳相形成和稳定化理论，为优化和开发高质量、高稳定性和高效率的低温渗氮工艺提供理论基础。

奥氏体不锈钢低温渗氮形成氮超高过饱和（10-35 at.%）改性层，具有优异的耐磨损抗腐蚀复合性能。为了推广这项技术的应用，迫切需要建立过饱和渗氮层完备的原子尺度结构模型，阐明渗氮层亚稳相的形成和稳定化机制，在此基础上揭示耐磨抗蚀复合改性机制。. 本项目提出奥氏体不锈钢过饱和渗氮层具有微纳尺度多级结构，并按计划顺利开展研究。在阐明短程有序结构相关基础科学问题的同时，将研究思路推广应用于碳钢界面短程有序结构和光催化材料表面短程有序结构，以及应力场对团簇结构的影响等方面，验证了研究成果在基础科学上的普适性，超额完成了预期目标。.采用自主知识产权的等离子体源离子渗氮技术改性处理304L奥氏体不锈钢，应用电子显微学方法，系统表征渗氮层中层错簇和团簇的成分和结构特征。应用第一性原理计算，阐明FCC基体和层错簇中团簇结构和团簇间相互作用规律，获得短程有序结构的具体结构特征，确认八面体团簇Fe6-nCrnN单元结构中，Cr原子倾向于在团簇中成对出现，共轭分布。. 系统表征非均匀短程有序结构在渗氮层的分布规律，建立微纳多级结构模型。其中零级结构（n = 0）为多晶渗氮层；一级结构（n = 1）为渗氮层中间隔分布的微米尺度层错簇和FCC基体；二级结构（n = 2）为层错簇区域和FCC基体中的纳米非均匀短程有序结构，由八面体团簇(Fe,Ni,Cr)6N以不同方式组合形成。. 在结构模型基础上，计算模拟了温度、合金元素和应力场对FCC基体和层错簇中团簇结构和短程有序结构的形成和稳定性的影响，探讨了辐照环境下过饱和渗氮层结构稳定性。渗氮层亚稳相稳定化机制是一种成分驱动通过高浓度的Cr、N原子形成短程有序结构所实现的稳定化机制。过饱和渗氮层亚稳相的稳定化主要与Cr、N浓度、温度和残余应力的释放有关。. 本项目建立了氮浓度、层错簇和非均匀短程有序结构与耐磨抗蚀性能的内在科学关联，研究结果将丰富和发展合金化表面亚稳相形成和稳定化理论，为优化和开发高质量、高稳定性和高效率的低温渗氮工艺提供理论基础。