Measerement of Intrinsic Diffusion Confficients in Intevrmtallics using Analytical Electon Microscopy

在NiAl（β相）与Ni（γ相）耦合的情况下进行扩散实验。分析电子显微镜用于检查微结构特征、晶体学取向和整个界面的成分变化。研究结果如下：1.扩散退火过程中，Ni_3Al基金属间化合物相（γ '相）在Kirkendall界面处生成并长大，γ'相在1273 K以上的退火温度下以抛物线规律向γ相生长，并保持与γ相相同的取向，γ/γ '界面光滑平直。在低于1273 K的退火温度下，随着退火时间的4次方，γ '相向γ相和β相生长。在γ/γ ′界面和γ ′/β界面处不存在相同的取向。两种界面均呈现波浪形和不规则形状。3.通过扩散偶界面上的成分变化测量了γ、γ '和β相的互扩散系数。在低于1273 K的温度下退火时，相应相的互扩散系数与单相扩散偶和两相扩散偶的互扩散系数的测量值一致，这是由于晶界扩散的影响。如果单晶Ni用作电偶的端元，则可以产生3Al。

Diffusion experiments were conducted on NiAl (beta phase) coupled with Ni (gamma Phase). Analytical electron microscopy is used to examinc microstructural features, crystallographie orientation and cmpositional variation across the intcrface. The results are summarized as below.1.The Ni_3 Al-based intermetallic phase (gamma' Phase) formed at the Kirkendall interface and grew during diffusion annealing.The gamma' phase grew towards the gamma phase following a parabolic law and kept the same orientation with the gamma phase at annealing temperatures higher than 1273 K.The gamma/gamma' interface was smooth and straight. At annealing temperatures lower than 1273 K,the growth of the gamma' phase occurred towards the gamma phase and the beta phase with a 4th power of annealing time. The same orientation did not exist at the gamma/gamma' interface and the gamma'/beta interface. Both interfaces exhibited wavy and irregular configurations.3.Interdiffusion coefficients of the gamma, gamma'and beta phases were measured from the compositional variations across the diffusion-couple interface. The interdifhsion coefficients in the corresponding puases were consistent with the published values measucd from single-phase diffusion cmplcs and two-phase diffusion couples cxccpt when the couples were annealed at at temperatures lower than 1273 K.This exception arose from the effect of grain boundary diffusion.4.It was suggested that a single crystal of Ni_3 Al can be produced if single crystalline Ni is used as an end member of the couple.