Plasmon energy changes in FeMo14C15B6Erx (x=0-2) bulk metallic glass during in-situ heating

Variations of volume plasmon energy of both ribbon and bulk FeMo14C15B6Erx (x=0-2) metallic glasses were measured as a function of the temperature in an analytical transmission electron microscope using valence electron energy loss spectroscopy (VEELS). The plasmon energy was found to decrease with increasing temperature, due not only to thermal expansion but also to chemical reordering in the glasses. The chemical reordering stimulates a specific solute cluster formation; M23(C, B)6 solute clusters began to form above about 200°C in both ribbon and bulk FeMo14C15B6Erx (x=0, 0.5, 1) metallic glasses. The formation of the M23(C, B)6 solute clusters was only found above 400°C in the ribbon FeMo14C15B6Er2 metallic glass, indicating inhibition of the M23(C, B)6 solute clusters occurred owing to the formation of Er-(C, B) complexes/clusters. The Er-(C, B) complexes/clusters were formed in the cooling process of the sample fabrication. In contrast to the ribbon sample, the formation of the M23(C, B)6 solute clusters did not occur in the bulk FeMo14C15B6Er2 metallic glass during heating. The amount of the Er-(C, B) complexes/clusters in the bulk sample was larger than that in the ribbon sample because of the slow cooling rate in the bulk sample fabrication. Because the solute carbon and boron atoms were mostly consumed by the formation of Er-(C, B) complexes/clusters in the bulk FeMo14C15B6Er2 metallic glass, the formation of M23(C, B)6 solute clusters was suppressed. This study demonstrates that chemical reordering during the relaxation of metallic glasses can be detected by the VEELS, providing valuable insight into the relaxation stage of metallic glass during heating.

本研究采用价电子能量损失谱（valence electron energy loss spectroscopy, VEELS）结合分析型透射电子显微镜，测定了薄带与块体FeMo₁₄C₁₅B₆Erₓ（x=0~2）金属玻璃的体积等离激元能量随温度的变化规律。研究发现，等离激元能量随温度升高而降低，该现象不仅源于热膨胀效应，同时与金属玻璃中的化学重排密切相关。化学重排会触发特定溶质团簇的形成：在薄带与块体FeMo₁₄C₁₅B₆Erₓ（x=0、0.5、1）金属玻璃中，M₂₃(C,B)₆型溶质团簇均在约200℃以上开始形成。而仅在薄带型FeMo₁₄C₁₅B₆Er₂金属玻璃中，M₂₃(C,B)₆型溶质团簇的形成仅在400℃以上才被观测到，这表明Er-(C,B)复合团簇的形成会抑制M₂₃(C,B)₆型溶质团簇的生成。Er-(C,B)复合团簇在样品制备的冷却过程中即已形成。与薄带样品不同，块体FeMo₁₄C₁₅B₆Er₂金属玻璃在加热过程中并未观测到M₂₃(C,B)₆型溶质团簇的形成。由于块体样品制备过程中的冷却速率更低，其内部Er-(C,B)复合团簇的含量高于薄带样品。在块体FeMo₁₄C₁₅B₆Er₂金属玻璃中，溶质碳、硼原子大多被Er-(C,B)复合团簇的形成所消耗，因此M₂₃(C,B)₆型溶质团簇的生成受到抑制。本研究证实，可通过价电子能量损失谱（VEELS）检测金属玻璃弛豫过程中的化学重排现象，为理解金属玻璃加热过程中的弛豫阶段提供了重要参考。