活性元素“晶界聚相”在金属高温氧化中的作用机制研究

(限3000字符) During the high temperature oxidation of metals, the grain boundaries diffusion of reactants through the thermally grown oxides layer usually dictates the rate at which the new oxides form and their characteristics, such as microstructure, and therefore affects the macro-scale progression of oxidation. One of the “Reactive elements effects” utilizes the segregation of reactive elements along the grain boundaries of the thermally grown oxides to reduce the grain boundary diffusion rate of the reactants, so as to improve the high temperature oxidation resistance of the materials. However, some knowledge of the grain boundaries of the thermally grown oxides is still missing: there is a missing mechanistic link between the macro-scale oxidation behavior and the micro-scale phenomenon. Besides the commonly-seen analyses on the oxidation kinetics, this project propose to introduce a novel theory in the area of grain boundary engineering: “grain boundary complexion” and its investigative techniques to the study of grain boundary-related phenomenon in high temperature oxidation of metals, and to carry out in-depth investigation on the segregation of reactive elements on the grain boundaries of the thermally grown oxides, aiming to obtain fundamental knowledge of reactive element grain boundary complexions. Meanwhile, we will utilize meso-scale statistical grain boundary characteristic distribution theories and methodology to characterize and calculate the grain boundary characteristic distribution of the thermally grown oxides, in order to establish the connection between macro-scale oxidation behavior and atomic-scale microstructure of reactive elements segregants. This proposed project would also employ computational simulation to investigate the effects of the formation of reactive element grain boundary complexions on the grain boundary diffusion of oxidation reactants. All of the proposed studies will greatly enrich and expand our understanding on the mechanisms of reactive element effects.

(限400字)金属的高温氧化过程中反应物在氧化层中的晶界扩散行为通常主导着新氧化物的生成速率、微观结构等特征，从而影响宏观氧化进程。“活性元素效应”之一就是利用活性元素在热生长氧化物的晶界偏聚而减缓反应物的固态扩散速率来改善金属材料的抗高温氧化性能。但目前的研究对氧化物晶界的认识缺乏能够联系宏、微观现象的根本机制。本项目引入晶界研究领域的新理论体系：“晶界聚相”及其研究方法来考察金属高温氧化中的晶界现象，在原子尺度上深入考察活性元素在热生成氧化物晶界的偏聚行为，获得对活性元素晶界聚相的基础认识；并且，将使用介观尺度的晶界特征统计学分布理论和研究方法，计算氧化物晶界的统计学特征，同时结合常规宏观氧化过程动力学分析，建立材料宏观氧化行为与活性元素原子尺度微观结构之间的联系。本项目还将利用计算机模拟考察晶界聚相的形成对氧化反应物的晶界扩散行为的影响，从根本上丰富和扩展对活性元素的作用机理的认识。

金属的高温氧化过程中反应物在氧化层中的晶界扩散行为通常主导着新氧化物的生成速率、微观结构等特征，从而影响宏观氧化进程。“活性元素效应”之一就是利用活性元素在热生长氧化物的晶界偏聚而减缓反应物的固态扩散速率来改善金属材料的抗高温氧化性能。本项目铁基和镍基的二元及三元合金在添加活性元素后的高温氧化行为进行了研究，分别对宏观氧化行为进行了常规氧化过程动力学分析，在介观尺度的上和更小的尺度上对热生成氧化物的晶界进行了表征，表征手段包括EBSD、TEM和AFM。本项目还使用了计算材料学的方法对热生成氧化物的生长和固态扩散模拟进行了尝试。目前取得的初步结果证实了一部分我们在计划书中提出的研究猜想。