晶界扩散对Ti-6Al-4V中α 相溶解的相场模拟

The Phase Field Simulation of Effect of Grain Boundary Diffusion on α Phase Dissolution

摘要:

晶界作为溶质的快速扩散通道，在扩散控制的相变过程中起着重要作用。为了探索晶界扩散作用下的相变过程，本文将晶界扩散耦合到定量的扩散控制相场模型，研究了Ti-6Al-4V合金多晶体系中的晶界数量、α相的空间分布和尺寸分布等对α相溶解的影响。研究结果表明：晶界是溶质扩散的快速通道，晶界边数越多，α相溶解速度越快，即当α相位于三岔点时，α相溶解最快。而α相位于晶界上和α相均匀分布基体中时，两种情况下的α相溶解速度差别较小。与二维条件下α相溶解速度相比，三维条件下的晶界扩散对α相溶解的影响更加显著；当相变以溶质的体扩散为主时，α相的空间分布是影响α 相溶解的主要因素之一；但当相变以溶质的晶界扩散为主时，除了均匀尺寸分布外，其它尺寸分布对α 相溶解影响不显著。

Abstract:

The grain boundaries as a fast diffusion path for solutes play an important role in multi-component diffusion-controlled phase transformations. In order to study the phase transformations in consideration of the grain boundary diffusion, the diffusion along grain boundary is incorporated in the quantitative phase field model coupled with the Kim-Kim-Suzuki (KKS). An integration method was used to calculate the equivalent grain boundary diffusion in the phase field method. The thermodynamic and mobility data was obtained from Thermo-Calc and DICTRA software respectively. The effect of the number of grain boundaries, the spatial distribution and size distribution (PSD) of α phase on the α phase dissolution was researched in the paper. The results show that grain boundaries are a faster element diffusive path. The number of grain boundaries is larger, the kinetics of α phase dissolution is faster. Namely, the kinetics of α phase dissolution is fastest when phase located at triple junctions; However, the dissolution kinetics is little difference when α phase is on the grain boundary and distribute uniformly in the matrix. Compared to the phase dissolution rate in two-dimensional condition, the effect of the grain boundary diffusion on dissolution kinetics is more obvious in three-dimensional condition. When phase transformation is dominated by bulk diffusion of solute, the spatial distribution of α phase is a main factor affecting the α phase dissolution. But when phase transformation is dominated by grain boundary diffusion of solute, the effects of other size distributions on the dissolution of alpha phase are not obvious except for uniform PSD.