金属材料表面纳米化研究与进展

大多数金属材料的失效都是从其表面开始的，进而影响整个材料的整体性能。研究表明，在金属材料表面制备纳米晶，实现表面纳米化，可以提升材料的表面性能，延长其使用寿命。金属材料表面纳米化是指利用反复剧烈塑性变形让表层粗晶粒逐步得到细化，材料中形成晶粒沿厚度方向呈梯度变化的纳米结构层，分别为表面无织构纳米晶层、亚微米细晶层、粗晶变形层和基体层，这种独特的梯度纳米结构对金属材料表面性能的大幅度提升效果显著。根据国内外表面纳米化的研究成果，首先对表面涂层或沉积、表面自纳米化以及混合纳米化3种金属表面纳米化方法进行了简要概述，阐述了各自优缺点，总结了表面自纳米化技术的优势，在此基础上重点分析了位错和孪晶在金属材料表面自纳米化过程中所起的关键作用，提出了金属材料表面自纳米化机制与材料结构、层错能大小有着密不可分的联系，对金属材料表面自纳米化机制的研究现状进行了归纳；阐明了表面纳米化技术在金属材料性能提升上的巨大优势，主要包括对硬度、强度、腐蚀、耐磨、疲劳等性能的改善。最后总结了现有表面强化工艺需要克服的关键技术，对未来的研究工作进行了展望，并提出将表面纳米化技术与电镀、气相沉积、粘涂、喷涂、化学热处理等...

Research and Progress on Surface Nanocrystallization of Metallic Materials

It is well known that the failure of most metallic materials starts from their surfaces, which in turn affects the overall performance of the whole material. Numerous studies have shown that the preparation of nanocrystals on the surface of metallic materials, i.e., surface nanosizing, can enhance the surface properties of materials and extend their service life. Surface nanosizing of metallic materials makes use of repeated violent plastic deformation to make the surface coarse grains gradually refine to the nanometer level, forming nanostructured layers with gradient changes of grains along the thickness direction, including surface non-woven nanocrystalline layer, submicron fine crystal layer, coarse crystal deformation layer and matrix layer, and this unique gradient nanostructure is effective for the significant improvement of surface properties of metallic materials. The process technology and related applications of nanocrystalline layers on the surface of metallic materials in China and abroad are introduced, and the research progress of high-performance gradient nanostructured materials is discussed. Starting from the classification of the preparation process of gradient nanostructured materials and combining with the research results of surface nanosizing in China and abroad, a brief overview of three methods of metal surface nanosizing, namely, surface coating or deposition, surface self-nanosizing and hybrid nanosizing, was given, the advantages and disadvantages of each were discussed and the advantages of surface self-nanosizing technology were summarized. On the basis of this, the key role of dislocations and twins in the process of surface self-nanitrification of metallic materials was analyzed, and the mechanism of surface self-nanitrification of metallic materials was inextricably linked to the material structure and the size of layer dislocation energy, and the current research status of the mechanism of surface self-nanitrification of metallic materials was summarized. Finally, the key technologies required to be overcome in the existing surface strengthening process were summarized, and future research work was prospected. It was proposed to combine surface nanosizing technology with some existing surface treatment technologies such as electroplating, vapor deposition, tack coating, spraying, chemical heat treatment, etc., to replace the high-cost manufacturing technologies and prepare inexpensive complex-phase surface layers with more excellent performance. Techniques for the preparation of gradient nanostructured materials include surface coating or deposition, surface self-nanosizing, and hybrid surface nanosizing. Surface coating or deposition technology has the advantages of precise control of grain size and chemical composition, and relatively mature process optimization, etc. However, because the coating or deposition technology adds a cover layer on the material surface, the overall size of the material increases slightly, and there is a certain boundary between the coating and the material, and there will be defects in the specific input of production applications. In addition, the thickness of the gradient layer prepared by this technology is related to the deposition rate, which takes several hours to prepare a sample. The surface self-nanitrification technique, which generates intense plastic deformation on the surface of metal materials, has the advantages of simple operation, low cost and wide application, low investment in equipment and easy realization of unique advantages. The nanocrystalline layer prepared on the surface of metal materials with the surface self-nanitrification technique has a dense structure and no chemical composition difference from the substrate, and no surface defects such as pitting and pores, but the thickness of the gradient layers and nanolayers prepared by this technique as well as the surface quality of the material vary greatly depending on the process. Hybrid surface nanosizing is a combination of the first two techniques, in which a nanocrystalline layer is firstly prepared on the surface of a metallic material by surface nanosizing technology, and then a compound with a different composition from the base layer is formed on its surface by means of chemical treatment. To realize the modern industrial application of this new surface strengthening technology, it is still necessary to clarify the strengthening mechanism and formation kinetics of surface nanosizing technology as well as the effect of process parameters, microstructure, structure and properties on the nanosizing behavior of the material. For different nanosizing technologies, the precise numerical models for nanosizing technologies need to be established and improved, and the surface self-nanosizing equipment suitable for industrial scale production needs to be developed. In the future, surface nanosizing technology will be combined with some existing surface treatment technologies (e.g. electroplating, vapor deposition, adhesion coating, spraying, chemical heat treatment, etc.) to prepare a complex phase surface layer with more excellent performance, which is expected to achieve a greater comprehensive performance improvement of the surface layer of metal materials.