金属玻璃微观形貌对晶化过程的影响

The effect of the microstructure of metallic glasses on the crystallization process

使用电解双喷法制备了金属玻璃中的环状和带状结构,利用扫描透射电子显微镜(STEM)、X射线能谱(EDS)和电子能量损失谱(EELS)等手段,没有发现明显的相分离现象,证实这些结构主要是样品厚度起伏导致的衬度变化。进一步原位退火实验表明,这些环状或条带状结构在加热后发生了明显地相分离,其中Ni和Cu元素聚集在厚区和薄区的交界处,产生了明显的偏聚现象,而Al的偏聚现象并不明显。这表明金属玻璃中的微观结构形貌可以显著地影响金属玻璃在晶化过程的相分离,局域偏析可能与Cu和Ni在厚区与薄区交界处优先成核有关,同时表面扩散速率与体扩散速率的差异也是导致晶化后元素浓度变化的原因之一。

The annular and striped features in the bulk metallic glass samples thinned by electropolishing are researched by the means of scan transmission electron microscopy （ STEM ） , energy dispersive spectrometry （ EDS ） and electron energy-loss spectroscopy （ EELS） . The results show that these features are resulted from thickness variation of samples instead of phase separation. Further in-situ observation of the annealing sample shows that remarkable phase separations emerge in the annular or striped features;in addition, Ni and Cu concentrate on the boundary between the thicker and thinner area and significant segregation of them is observed, while the segregation of Al is unobvious. The observation indicates that the microstructures of metallic glasses have an significant effect on the phase separation in the crystallization process, and the local segregation is probably related to the preferred nucleation of Ni and Cu on the boundary between the thicker and thinner area. Also, the difference between surface diffusion and bulk diffusion is one of the factors that account for the element concentration variation in the crystallized alloy.