For the first time, the analytical electron microscopy has been used to determine the solute concentration profiles left behind the moving reaction front (RF) of the discontinuous precipitation (DP) reaction in a Fe-13.5 at.% Zn alloy. These profiles have been converted into grain boundary diffusivity (sδD_b) values, using Cahn’s diffusion equation in its original form and the data of the growth rate of the discontinuous precipitates obtained from independent measurements. This approach has essentially removed existing difference in comparison to sδD_b values obtained from Cahn′s simplified and Petermann–Hornbogen models relevant for the global approach to the DP. Simultaneously, the local values of sδD_b have been up to 8–10 orders of magnitude higher than the data for volume diffusion coefficients and much greater than for diffusion at the stationary grain boundaries of Zn in pure Fe. This is clear indication that the rate controlling factor for DP reaction in the Fe-13 at.% Zn alloy is diffusion at the moving RF.

中文翻译：

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Fe-13.5 at。％Zn合金中不连续析出的微观分析研究

分析电子显微镜首次用于确定Fe-13.5 at。％Zn合金中不连续沉淀（DP）反应的移动反应前沿（RF）后面的溶质浓度分布。这些简档已被转换成的晶界扩散率（sδD _b）值，并使用在其原始形式的Cahn的扩散方程，并从独立的测量中获得的不连续析出物的生长速率的数据。这种方法基本上已经删除现有的相比差别sδD _b从有关全球的方法来DP卡恩的简化和彼得曼-Hornbogen模型得出的值。同时，当地的价值观sδD _b比体积扩散系数的数据高8-10个数量级，比纯铁中Zn固定晶界的扩散大得多。这清楚地表明，Fe-13 at。％Zn合金中DP反应的速率控制因素是在移动RF处的扩散。