原子尺度下核电用Fe-Ni-Cr耐蚀合金动态应变时效微观机制研究

Under the working conditions of nuclear reactor with high temperature and high pressure, dynamic strain aging is likely to occur in the Fe-Ni-Cr corrosion resistant alloy (CRA) for heat exchanger tube of steam generator, which is severely detrimental to the strength and toughness of CRA. For a better control of the mechanical properties for CRA under the working conditions of nuclear reactor, this project is proposed to study the micro-mechanism of dynamic strain aging in CRA at the atomic scale, which can improve the traditional research methods of dynamic strain aging based on mathematical and physical models. The macroscopic mechanical characteristics of dynamic strain aging in CRA are thoroughly investigated through hot compression tests with constant strain rate and jumping strain rate to obtain the sensitive deformation conditions of dynamic strain aging. By using microstructural characterization techniques of atom probe tomography and high resolution transmission microscope, we firstly determine the types of solute atoms and their diffusion modes which result in the serrated flow behavior (PLC effect) during hot deformation of CRA. We also explore the motion and distribution characteristics of mobile dislocations. Additionally, we study the mechanism of “pseudo-PLC effect” induced by precipitation and subsequently reveal the effect of dynamic softening on the disappearance of PLC effect. Based on the above work, the micro-mechanism of dynamic strain aging in CRA is studied at the atomic scale from multiple respects. The research results of this project can contribute to enhance the safety and stability of heat exchanger tube manufactured by CRA. Besides, these results would provide the theoretical basis and technical support for the development and application of new generation CRA materials in nuclear reactor.

在核反应堆高温高压工况下，蒸汽发生器传热管用Fe-Ni-Cr耐蚀合金容易发生动态应变时效行为，严重影响其强度、韧性等性能。为了更好地控制耐蚀合金在核反应堆运行条件下的力学性能，本项目在原子尺度下对其动态应变时效微观机制进行研究，对传统的基于数学物理模型的研究方法做出改进。通过恒定/跳跃应变速率热变形实验，研究耐蚀合金动态应变时效宏观力学特点，确定动态应变时效敏感变形条件。利用原子探针层析技术、高分辨透射电镜等微观表征技术，确定诱发锯齿屈服现象（PLC效应）的溶质原子种类及其扩散方式，分析可动位错的运动和分布特点，研究析出相诱导“伪PLC效应”的机理，揭示动态软化对PLC效应消失的影响规律。在此基础上，实现在原子尺度下对耐蚀合金动态应变时效微观机制的多角度研究。项目研究成果有助于提高耐蚀合金传热管的安全性和稳定性，为新一代核电用耐蚀合金材料的开发和应用提供理论依据和技术支持。

在核反应堆高温高压工况下，蒸汽发生器传热管用Fe-Ni-Cr耐蚀合金容易发生动态应变时效（DSA）行为，严重影响其强度、韧性等性能。在本项目的研究工作中，首先，我们通过对核反应堆服役温度条件下典型耐蚀合金热变形宏观力学行为的研究，确定了DSA敏感变形条件范围：对于800H合金，当应变速率为0.001s-1时，DSA温度区域分布在500~750℃；当应变速率为0.01s-1时，DSA温度区域分布在550~790℃；当应变速率为0.1s-1时，DSA温度区域分布在600~840℃。对于253MA合金，当应变速率为0.001s-1时，DSA温度区域分布在550~700℃；当应变速率为0.01s-1时，DSA温度区域分布在600~750℃；当应变速率为0.1s-1时，DSA温度区域分布在700~790℃。其次，我们利用基于原子尺度的先进微观组织表征技术，结合DSA激活能的计算结果，从可动位错的运动特点和溶质原子的扩散方式两个角度，直观地揭示了耐蚀合金中DSA微观机制：800H合金的DSA激活能为194kJ/mol，253MA的DSA激活能为242kJ/mol。原子尺度的微观组织分析结果显示，Cr、Ni、Ti等置换固溶原子在位错线附近的偏聚导致了DSA效应的发生。最后，我们还结合动态回复过程中位错组态的演变规律以及不同温度条件下典型碳化物的析出特点，分析了DSA效应消失的机理：动态软化过程的发生增加了可动位错的消失速率，位错的缠结导致胞状亚结构的形成，显著降低了晶粒内部的位错密度。此外，碳化物的大量析出会导致局部基体中Cr、Ti等溶质原子浓度的减小，消耗了溶质原子气团的数量，对DSA效应的消失也产生了一定贡献。