高锰TRIP/TWIP钢中形变马氏体与形变孪晶的原位透射电镜研究

High Mn TRIP/TWIP steels are currently one of the most attractive materials for lightweight structural applications in the automotive industry. Their excellent combination of strength and elongation depends on martensite and twins produced during plasitic deformation. However, the formation of deformation martensite and twins is largely effected by chemical composition, microstucture and deformation conditions. The key to clarify these factors lies in the understanding of the nucleation and growth process of deformation martensite and twins, as well as their competition evolution. It has long been difficult to carry out in-situ observations of the evolution of deformation microstructures at the microscale or even atomic scale, which is actually a bottle-neck to well understand the alloys. This project aims to make a breakout at this technical bottle-neck, using advanced atomic-resolution imaging techniques inculding in-situ tensile and heating techniques. In association with process optimizations and property measurements as well as energy calculations, this project also aims to reveal the evolution of deformation microstructures in real time, in order to understand the structure-property-process relations of the alloys. These research results will provide a scientific basis for the design of high Mn TRIP/TWIP steels and their application in automotive manufacturing materials, at the same time, they are of great significance to enrich the theory of phase transformation in metal materials.

高锰TRIP/TWIP钢是汽车工业中极其重要的轻量化结构材料。该合金优异的综合力学性能来源于变形过程中产生的马氏体和形变孪晶。而形变马氏体和形变孪晶的形成与材料的化学成分、组织结构、变形条件等因素密切相关。厘清这些影响因素的关键在于认识形变马氏体和形变孪晶的形核与生长过程，以及它们的竞争演变规律。过去很难实现在微观尺度上对形变产物的演变过程进行原位跟踪观察，本项目针对这一问题，拟利用先进原子成像电镜平台技术，包括原位电镜拉伸和加热技术，结合块体材料的工艺调控和性能表征以及能量计算，较为彻底地阐明高锰TRIP/TWIP钢中形变微观组织的演变规律，理解结构、性能和工艺之间的关系，为高锰TRIP/TWIP钢的设计及其在汽车制造材料中的应用提供科学依据，同时对丰富金属材料的相变理论体系具有重要意义。

高锰TRIP/TWIP钢是汽车工业中极其重要的轻量化结构材料。该合金优异的综合力学性能来源于变形过程中产生的马氏体、形变孪晶等相变产物。过去很难实现在微观尺度上对这些变形产物的演变过程进行原位跟踪观察，本项目针对这一问题，利用先进原子成像电镜平台技术，包括原位电镜拉伸技术，结合块体材料的工艺调控和性能表征，较为彻底地阐明了高锰TRIP/TWIP钢中变形微观组织的演变规律，加深了对结构、性能和工艺之间关系的理解，取得了以下重要研究成果：厘清了化学成分、晶粒尺寸、温度、变形方式等因素对形变孪晶和马氏体形成的协同作用；系统阐述了这类钢在温度和晶粒尺寸下层错能和强韧化机制的变化规律；揭示了一次形变孪晶和二次形变孪晶的形核机制；厘清了高应变速率冲击变形下高锰TRIP/TWIP钢的变形产物和变形机制。本项目为高锰TRIP/TWIP钢的设计及其在汽车制造材料中的应用提供科学依据，同时对丰富金属材料的相变理论体系具有重要意义。