基于Voronoi微观晶粒结构确定Fe-Si合金中硅的晶界扩散系数

Determination of Fe-Si Alloy Grain Boundary Diffusivity of Silicon Based on Voronoi Grain Microstructure

铁基体中渗硅是生成高硅钢材料的主要方法,但现有的硅扩散过程分析往往只考虑整体的扩散效果,忽略了微观晶粒间与晶粒内的扩散差异。为了研究晶界对于扩散的影响,本文基于Voronoi图建立三维微观模型模拟了晶粒间与晶粒内的硅扩散行为。通过化学气相沉积实验、扫描电镜以及能谱元素分析测量计算得到材料微观结构参数和晶粒内的体扩散系数Dg。通过实验得到晶界宽度、晶粒尺寸等材料微观结构,在此基础上用有限元计算获得微观体积元中晶界的扩散系数Dgb。实验与模拟结果均表明硅在铁晶粒与晶界内的扩散存在明显差异,晶界扩散速率为3.3×10-3 mm2/s,大致是体扩散速率的103~104倍,通过晶界扩散入基体的硅通量达到总通量的近三分之一,因此增大晶界体积分数对提高CVD渗硅效率和渗硅量有着重要作用。

Silicon diffusing into iron base alloy is the main way to generate high silicon steel materials, however,the accurate analysis of silicon diffusion process is often considered as a whole diffusion effect, ignoring the microscopic diffusion differences in the grain and grain boundary（GB）. In order to study the effects of grain boundaries for diffusion, a 3D microscopic model based on Voronoi structure is applied to simulate the process of intergranular and GB diffusion. The body diffusion coefficient （Dg） in the inner grain and material microstructural parameters can be provided by chemical vapor deposition （CVD） experiment, scanning electron microscopy （SEM） and energy spectrum analysis （EDS）. Based on the material microcosmic parameters including grain boundary width and grain size, grain boundary diffusion coefficient （,Dgh） of micro representative volume element can be obtained. The results of the experiment and simulation effectively show Silicon diffusion in Fe grain and grain boundary have obvious differences. The Dgb value is 3. 3 × 10-3 mm2/s, roughly 103 - 104 times as high as Dg. The silicon flux through grain boundary diffusion into alloy is reached nearly a third of total flux,so increasing the volumetric fraction of grain boundary can play an important role in improving efficiency and silicon quantity of CVD siliconizing.