机械研磨对电场作用下表面渗镀的影响及作用机制的研究

电场作用下的电荷表面富集效应，提高了金属材料表面的扩散能力和相变形核率，有效地促进了化学热处理过程；机械研磨导致金属材料表面的晶粒细化、晶体缺陷及内应力，进一步强化了电荷表面富集效应的作用效果，以及表面的扩散能力，为改善金属材料表面渗镀层的组织结构特性、消除缺陷、提高性能提供了一条有效途径。本项目研究在这一过程中，机械研磨对金属表面电荷富集特性、阳离子选择性吸附、表面饱和扩散特性和渗镀层组织转变特性的影响，通过分别研究C和Al向基体的扩散特性和规律、计算扩散激活能和扩散系数，探讨机械研磨和电场促进扩散过程的作用机制及影响因素；通过分析渗镀过程的组织变化特性，探讨渗镀层合金化过程中相变的核形与长大规律，以及机械研磨与电场促进相变过程的作用机制。进而搞清楚这一过程中的离子选择性吸附、促进扩散、改变相变形核规律等的作用机制，为机械研磨和电场能够更广泛地应用于表面化学热处理领域提供理论依据。

The diffusion capability of cations and the nuclear rates of phase transformation will be apparently enhanced by applying electrical field in surface chemical heat-treatment of alloys due to the charges concentration on surface layer of alloys. Surface mechanical attrition processes (SMAT) induce ultra-fine grains, crystal defects and residual stress which will strengthen the effect of charges concentration. It’s a new approach to improve the microstructure of coatings, eliminate the defects in the surface layer and enhance the properties of alloys by combining the surface mechanical attrition processes with electrical fields..In this study, carburization and pack aluminizing on carbon steels will be carried out in the condition of various currents and surface mechanical attrition processes. The mechanism of diffusion and phase transformation will be investigated by characterizing the microstructure of the coatings and calculating the diffusion activated energy and coefficient. As charges concentrate on surface layer of alloys in electric field, there is a high energy region on the surface of substrates. The ultra-fine grains, crystal defects and residual stress induced by SMAT will further enhance the surface energy lever and cause lattice distortion. All these factors will promote diffusion processes and change the characteristics of phase transformation. Nucleation and growth of new phases will be depended on the surface effect and the interaction of different physical fields, which also determine the microstructure and properties of the coatings..In this study, the research will figure out the feature and mechanism of diffusion and the effects of the SMAT on the nucleation and growth of new phases. The results not only make us clearly understand the diffusion properties and the solid phase transition, but also give some theoretical guidance to apply this technology into surface cementation and chemical heat treatment areas.