The 3DAP is a very powerful tool that provides atomic scale elemental mapping of chemical heterogeneities in materials. Recently, it has been successfully employed to identify the presence of liquid phase separation in metallic glasses [14, 19]. For example, Hono’s group [14] revealed that nanoscale phase separation from the melt into Cu-enriched and was observed, since Ag−Cu has a positive heat of mixing (∆HAg−Cu= +2 kJ mol−1). Figure 5.4 (a) displays an atom map of the as-cast Nb0 metallic glass. It can be seen that the map exhibits an almost homogenous contrast. Apart from four constituent elements (Zr, Cu, Ni and Al), oxygen was also detected, mainly in the form of ZrO. In the current study, the needle-shaped specimens were prepared by electropolishing technique, which allows a possible route for oxygen uptake. Oxygen, being a mobile species, is able to diffuse further into the bulk specimen during process. It is expected that a part of oxygen in the map was from the process of specimen preparation. In order to get more details on local compositional variation, atom probe concentration depth profiles obtained from the Nb0 specimen are displayed in Figure 5.4 (b). One can see that all the constituent elements are uniformly distributed in the matrix, indicating that no phase separation occurred in the as-cast Nb0 alloy. We tried to run Nb0.5 alloy specimens several times, but unfortunately the data quality is not as good as Nb0. The specimens had quite thick oxides on the top which is
The 3DAP is a very powerful tool that provides atomic scale elemental mapping of chemical heterogeneities in materials. Recently, it has been successfully employed to identify the presence of liquid phase separation in metallic glasses [14, 19]. For example, Hono’s group [14] revealed that nanoscale phase separation from the melt into Cu-enriched and was observed, since Ag−Cu has a positive heat of mixing (∆HAg−Cu= +2 kJ mol−1). Figure 5.4 (a) displays an atom map of the as-cast Nb0 metallic glass. It can be seen that the map exhibits an almost homogenous contrast. Apart from four constituent elements (Zr, Cu, Ni and Al), oxygen was also detected, mainly in the form of ZrO. In the current study, the needle-shaped specimens were prepared by electropolishing technique, which allows a possible route for oxygen uptake. Oxygen, being a mobile species, is able to diffuse further into the bulk specimen during process. It is expected that a part of oxygen in the map was from the process of specimen preparation. In order to get more details on local compositional variation, atom probe concentration depth profiles obtained from the Nb0 specimen are displayed in Figure 5.4 (b). One can see that all the constituent elements are uniformly distributed in the matrix, indicating that no phase separation occurred in the as-cast Nb0 alloy. We tried to run Nb0.5 alloy specimens several times, but unfortunately the data quality is not as good as Nb0. The specimens had quite thick oxides on the top which is
Shuang%20thesis.docx