Diffusion Mechanism of Atoms in Ordered Alloys at Low Temperature

原子扩散现象的知识对于为现代技术开发新材料，然后使用由这些高度设计的材料制成的安全的机械和电子设备是必不可少的。二次铁质谱的足够分辨率已被证明可用于测量小扩散系数和低至相对较低温度的许多原子的同位素效应。本研究利用二次离子质谱仪的优势，阐明了低温下B2、DO_3和L_0型有序合金中几个溶质原子的小扩散系数、同位素效应和扩散机制。取得的主要结果如下。镍、钒、钛和硼在Fe-Al合金中的扩散系数与温度的关系不能用简单的Arrhenius关系来解释。钒、钛、硼的扩散系数受B2级的变化控制，而镍的扩散系数受DO_3级和B2级的影响。在Fe-Al合金中，在无序态和B2型和DO_3型有序状态下，B的同位素效应约为0.2。硼在Fe-Al合金中的扩散是通过高度关联的机制进行的。在CuAu合金中，有序态的硼的扩散系数不小于由无序态推算的扩散系数。无序态CuAu合金中B的同位素效应为0.1，L10型有序态中B的同位素效应为0.8。在无序状态下，硼的扩散关联比在有序状态下更强。

The knowledge of diffusion phenomena of atoms is essential to develop new materials for modern technologies and then to use safely mechanical and electrical equipments made from those highly designed materials. The sufficient resolution of secondary iron mass spectroscopy has proved to be available for determining the small diffusion coefficients and the isotope effects of many atoms down to relatively ll"ow temperature. Our research clarified the small diffusivities and the isotope effects and the diffusion mechanisms of several solute atoms in the ordered alloys of B2, DO_3 and L1_0 types at low temperatures, by using the profit of secondary ion mass spectroscopy. The main results obtained are as follows. The temperature dependences-of diffusivities of nickel, vanadium, titanium and boron in theFe-Al alloy were not explained by a simple Arrhenius relation. The diffusivities of vanadium, titanium and boron were controlled by the change of B2 order, while the diffusivity of nickel was determined by the changes of DO_3 order as well as B2 order. The isotope effect of boron was about 0.2 in the disordered state and the ordered states of B2 and DO_3 types in the Fe-Al alloy. The diffusion of boron proceeded through highly correlated mechanism in the Fe-Al alloy. The diffusivity of boron in the ordered state of the CuAu alloy was not smaller than that extrapolated from the disordered state. The isotope effect of boron in the CuAu alloy was 0.1 in the disordered state and 0.8 in the ordered state of L1_0 type. Correlation for the diffusion of boron was stronger in the disordered state than in the ordered state.