超高强度不锈钢中纳米析出相的调控及其对点蚀行为的影响

The stability and pitting corrosion sensitivity of the passive film are closely related to the composition and structure of Nano-sized precipitation in the ultra-high strength stainless steel. This project mainly studies the relationship between the structure of the passive film, the semiconductor characteristics and the alloy elements, aging system, environmental medium, and further explains the corrosion failure mechanism of the ultra-high strength stainless steel through the first-principles calculations and micro-area electrochemical techniques. In addition, the effects of the evolution law of the composition, structure and distribution form of the Nano-sized precipitation on the formation of the passive film and the pitting corrosion initiation are elaborated. This project focuses on obtaining the relationship between the band structure and the precipitation, substrate alloy by the combination of first-principles calculation, 3D atomic probe and scanning tunnelling microscope, and further establishing the atomic scale models of the passive film covered on the surface of the Nano-sized precipitation and the substrate. Subsequently, the passive film with excellent corrosion resistance will be designed actively by optimizing its composition and structure, and further to obtain excellent alloy system and preparation process for the ultra-high strength stainless steel. The project aims at elaborating the formation of passive film, its stability, rupture and pitting initiation mechanism. The project can provide theoretical support for the development of metal passivation theory system and provide novel ideas and approaches for the design and application of corrosion resistant ultra-high strength stainless steel.

本项目针对超高强度不锈钢中纳米析出相的组成、结构与其钝化膜稳定性和点蚀敏感性密切相关的特点，基于第一性原理计算、纳米尺度结构表征和微区电化学测试等，研究合金元素、时效制度、环境介质与钝化膜结构、半导体特性之间的关系。通过在钝化膜研究中引入微观组织特征分析，阐明纳米析出相成分、结构和分布形态等的演化规律及其对超高强度不锈钢表面氧化成膜、点蚀萌生等过程的作用机理。重点集成第一性原理计算与原子探针、电化学扫描隧道显微镜等纳米尺度表征技术，建立纳米析出相/基体表面氧化膜原子尺度模型，拟计算获得能带结构与析出相、基体合金之间关系，筛选出耐蚀性好的钝化膜组成和结构，主动设计、优化超高强度不锈钢的合金体系和制备工艺。旨在从原子尺度阐释超高强度不锈钢钝化膜的形成、稳定、破裂和点蚀萌生等过程机理。项目可进一步拓展超高强度不锈钢钝化理论体系的基础研究工作，为其材料设计和耐蚀性能提高提供新思路和新方法。

本项目针对超高强度不锈钢中纳米析出相的组成、结构与其钝化膜稳定性和点蚀敏感性密切相关的特点，基于第一性原理计算、纳米尺度结构表征和微区电化学测试等，研究了合金元素、时效制度、环境介质与钝化膜结构、半导体特性之间的关系。采用多种时效温度、时间和冷却工艺，制备了具有不同组织结构与纳米析出相的AM355、15-5PH、Custom465高强度不锈钢和自研新型超高强度马氏体不锈钢。通过在钝化膜研究中引入微观组织特征分析，阐明纳米析出相成分、结构和分布形态等的演化规律及其对高强度不锈钢表面氧化成膜、点蚀萌生等过程的作用机理。重点集成了第一性原理计算与三维原子探针、透射电镜和原子力开尔文力显微镜等纳米尺度表征技术，建立了铁基体表面氧化膜原子尺度模型。研究结果表明，以富镍Custom465钢为例，不锈钢的钝化和耐蚀性能随着时效过程中ɳ-Ni3Ti的析出和逆变奥氏体含量变化而改变，ɳ-Ni3Ti/基体界面处的低电位区域的宽度约为20 nm，基体与析出相之间最大Volta电势差为30mV。ɳ-Ni3Ti与基体之间的界面处钝化膜稳定性较低，可成为点蚀优先萌生的区域。随着ɳ-Ni3Ti相的粗化和长大，其与基体之间的界面处贫镍，同时ɳ-Ni3Ti相与基体之间的界面具有低的原子匹配度和高的界面能，进一步降低了析出相和基体的界面处钝化膜的耐蚀性。采用第一性原理计算，研究了合金元素Cr、Mo、N和Ti对NH3在α-Fe2O3上的吸附行为以及其对α-Fe2O3半导体性质的影响。阐明了不锈钢PREN公式中铬、钼、氮对提高不锈钢耐点蚀性能的微观机制，并探索其它有益于提高耐点蚀能力的元素，为开发新型耐点蚀不锈钢提供了思路。项目研究所获得的力学-耐蚀性能协同优化的时效工艺参数，已在新型超高强度不锈钢生产中获得应用。