梯度纳米结构奥氏体不锈钢中的马氏体相变研究

Deformation-induced martensitic transformation can improve dramatically the mechanical properties of strength and toughness of the metallic materials. Therefore, the study of deformation-induced martensitic transformation has extreme scientific significance and industrial application prospects. The surface mechanical attrition treatment (SMAT) has been widely used to fabricate the gradient nanostructured austenitic stainless steels, in which the deformation-induced martensitic transformation can always be activated. By using the high-resolution transmission electron microscopy (HRTEM), the previous works of the applicant have successfully revealed the atomic movement mechanism of the martensitic transformation of fcc→hcp→bcc in SMATed gradient nanostructured 304 stainless steels, which for the first time verified experimentally a classic half-century-old Bogers-Burgers martensitic transformation model at atomic-scale. However, the atomic movement mechanisms of other types of deformation-induced martensitic transformation have not yet been revealed in the SMATed gradient nanostructured stainless steels. In this proposal, with the same methodology, the HRTEM will be mainly employed to dissect the atomic movement mechanisms of other types of deformation-induced martensitic transformation in the gradient nanostructured austenitic stainless steels. Then, the thermodynamics energy model of associated martensite nucleation will be built-up to elucidate the intrinsic relationship between the microstructure of martensitic transformation and the temperature, composition, and the parameters of SMAT process, which will guide theoretically the optimal of the combination of the parameters of thermomechanical treatment-microstructure-mechanical properties.

形变诱发马氏体相变可以增强增韧金属材料的机械性能，因而研究形变诱发马氏体相变具有重大的科学意义和工业应用前景。表面机械研磨处理（SMAT）技术制备梯度纳米结构奥氏体不锈钢时，常伴随形变诱发马氏体相变的发生。利用高分辨透射电子显微镜（HRTEM），项目申请人前期工作已成功揭示 SMAT 梯度纳米结构 304不锈钢中形变诱发马氏体相变fcc→hcp→bcc的原子运动机制，首次在原子尺度上实验证实了半世纪前提出的Bogers-Burgers经典马氏体相变模型。然而，该材料中其它马氏体相变类型的原子运动机制尚未被揭示。本项目拟继续运用HRTEM，剖析梯度纳米结构奥氏体不锈钢中其它马氏体相变类型的原子运动机制；并以此建立相应马氏体相变在热力学上的能量模型，阐明其微观组织结构与温度、成分和SMAT参数之间的内在联系；从而为调控优化形变热处理参数-马氏体组织-宏观机械性能组合提供理论指导。

金属材料的马氏体相变具有相变诱发塑性、形状记忆、和增强增韧等特性。20世纪以来，马氏体相变材料仍然得到了迅速发展，成为航空、航天、医疗、能源、电子等一些高科技领域关键设备的核心材料。但是，形变诱发马氏体相变过程中的原子运动机制、热力学能量模型以及微观组织结构与温度、成分和外载之间的内在联系等一些关键科学问题仍待深入研究。本项目主要运用和发展梯度纳米结构制备方法、高分辨透射电镜、分子动力学模拟、热力学分析和相场模拟等研究手段，在马氏体相变及其塑性变形等关键科学问题上取得重要进展。例如，研究表面剧烈塑性变形技术制备梯度纳米结构金属的形成机制，重点剖析梯度纳米结构奥氏体不锈钢中几种多相马氏体相变中相界面的原子排列和晶体缺陷等关键信息，揭示其相变的原子运动机制；阐明纳米析出相与基体相fcc/bcc相界面处的晶体缺陷对高强马氏体钢的性能影响；原子尺度模拟和能量分析理解铁单晶在断裂过程中裂纹尖端处的马氏体相变路径及其原子运动机制；热力学分析和相场模拟在能量上研究成分对马氏体相变的诱发及其力学性能的影响；发展原位高分辨透射电镜力学加载装置研究纳米结构金属材料中依赖晶粒大小的塑性变形机制。以上重要进展对实现纳米结构金属材料的高强度-延展性匹配的机械性能提供有益参考。在项目支持下，研究团队已在Acta Materialia，Scripta Materialia，Journal of Materials Science & Technology，Journal of Magnesium and Alloys，Journal of Materials Science和Journal of Alloys and Compounds等国际著名专业期刊上发表学术论文14篇，申请专利1项，在国内外马氏体相变及塑性变形领域产生了一定影响。