Probing rare earth segregation in steels

The challenge of characterizing the precise sites of rare earth (RE) atoms has limited our understanding of microalloying and the design of RE steels with superior performance in recent decades. Electron microscopy with near-atomic resolution can be used to identify RE retention or trapping in alloys but fails to provide reliable results in steel due to the extremely low solid solubility of RE atoms. Here, we probed the segregation and clustering of RE atoms by identifying the location of RE oxides via the in situ oxidation of these extremely active atoms in dendritic regions, ultimately providing direct visualization of the distribution of RE atoms. Firstprinciples calculations confirmed that dendritic interfaces can serve as trapping sites for solute RE atoms. These findings effectively solve the problems caused by the use of traditional techniques to characterize RE atoms in steels and provide the first evidence for a solid solution of RE atoms.

近几十年来，精准表征稀土（Rare Earth, RE）原子精确位点的难题，限制了我们对微合金化过程的理解以及高性能稀土钢的设计研发。近原子分辨率电子显微镜可用于识别合金中稀土原子的固留或俘获行为，但由于稀土原子在钢铁中的固溶度极低，该技术无法在钢铁体系中得到可靠的表征结果。本研究通过在枝晶区域对这些活性极强的稀土原子进行原位氧化，从而定位稀土氧化物，以此探究稀土原子的偏聚与团簇行为，最终实现了稀土原子分布的直接可视化。第一性原理计算证实，枝晶界面可作为溶质稀土原子的俘获位点。本研究成果有效解决了传统表征技术在钢铁中稀土原子表征时面临的难题，并首次为稀土原子固溶体提供了实验证据。