La、Ce对马氏体时效钢中NiAl相析出及热稳定性的影响机理

马氏体时效钢是超高强度钢中性能最为优异的钢种之一。通过合理的成分与热处理工艺设计，利用显微组织与析出相调控可实现高强韧性的良好配合。前期研究中制备的稀土马氏体时效钢，在适当降低Ni、Mo含量后仍能保持优良的强韧性水平，且NiAl析出相热稳定性提高，但目前其机制与作用规律尚不清楚。本项目拟设计系列稀土马氏体时效钢，借助球差校正透射电镜与三维原子探针分析，研究时效过程中稀土及其他合金元素在NiAl/bcc-Fe体系的原子尺度分配与亚晶格占位，阐明稀土对界面错配度与界面能的影响规律；通过蒙特卡罗方法与扩散偶实验，结合第一性原理探清La、Ce对Ni、Al扩散行为的影响机理；借助电子显微分析和分子动力学方法，研究NiAl相与位错的交互作用机制。在此基础上，建立考虑界面能与扩散的析出动力学模型，揭示La、Ce对NiAl相析出及热稳定性的影响机制，这对于低成本马氏体时效钢的开发具有重要理论与实际意义。

Maraging steel is one of the most excellent steels in ultra-high strength steels. Through the reasonable composition and heat treatment process design, one can achieve a good match of high strength and toughness via manipulating the microstructure and precipitation phase. Previous study of rare earth containing maraging steels indicates that the alloy can maintain excellent level of strength and toughness after proper reduction of Ni and Mo content, and the thermal stability of NiAl precipitation phase is improved, but the corresponding mechanism and law are still unclear. This project intends to design a series of RE containing maraging steels, and using spherical aberration corrected transmission electron microscope, three-dimensional atom probes analysis, to investigate the atomic-scale distribution and sub lattice occupancy of rare earths and other alloying elements in the NiAl/bcc-Fe system during the aging process, consequently elucidate the influence of rare earth on interface mismatch and interface energy. Based on the first-principles calculation, combined with Monte Carlo method and diffusion couple experiment, the effect of La and Ce on the diffusion behavior of Ni and Al is analyzed. The interaction mechanism between NiAl phase and dislocation is studied by means of electron microscopic analysis and molecular dynamics. On this basis, a precipitation dynamic model considering the interfacial energy and diffusion coefficient will be established, and the dominant mechanism of the effect of La and Ce on the precipitation and stability of NiAl phase will be elucidated, which is of theoretical and practical significance to develop low-cost maraging steel.