基于微观偏析统一模型及Thermo-Calc的三元合金凝固路径耦合计算

THERMO-CALC LINKED COMPUTATIONS OF SOLIDIFICATION PATHS OF TERNARY ALLOYS USING AN EXTENDED UNIFIED MICROSEGREGATION MODEL

将合金凝固微观偏析统一模型推广到三元合金凝固微观偏析的预测,并提出了能够计算三元匀晶与共晶合金凝固路径的数值计算方法.实现了在源代码层次上与热力学计算软件Thermo-Calc及其数据库的耦合,以获取多元合金凝固路径计算所需的凝固热力学数据.通过Fe-40V-40Cr,Al-4.5Cu 1.0Si.Al 10Cu 2.5Mg和Al-1.49Si-0.64Mg(质量分数,%)等多元/多相合金在不同冷速下凝固路径的实例计算,以及与相应的凝固组织定量金相实验结果对比,验证了本文多元/多相凝固模型和算法的正确性.

A model for predicting the microsegregation of ternary alloys was developed via extending a previously proposed unified microsegregation model for binary alloys. The present multicomponent/multiphase model retains the advanced features of the previous binary microsegregation model, in which the unified microscale parameter Ф takes a general function form to account for more possible influential factors, including the partition coefficient, solid fraction, solid diffusion coefficient, dendrite geometrical morphologies and solidification rate, etc. The algorithms for calculating the solidification paths of ternary isomorphous and eutectic alloys were proposed, which closely couples with a commercial software package/database of Thermo-Calc via its TQ6-interface in order to directly access to thermodynamic data needed in the multicomponent/multiphase solidification path computations. In the solidification of primary phase and three phases eutectic, solid fraction fs was selected to be a control variable when solving the equations of the microsegregation models, while in the solidification of two phases eutectic, temperature was selected to be a control variable as the relationship between the concentrations of solutes B and C was unknown. In each calculation iterative step, the names and number of the equilibrium phases were obtained from Thermo-Calc, and then saved and compared with the calculation results of the previous step. As the names and number of the equilibrium phases in each solidification stage of ternary eutectic alloys are different, the three solidification types were determined by comparing with the results in the computation process. The availability and reliability of the proposed multicomponent/multiphase model and algorithms were demonstrated by sample computations for the solidification paths of Fe-40V-40Cr, A1-4.5Cu-ISi, AI-10Cu 2.5Mg and Al-l.49Si-0.64Mg （mass fraction, %） alloys under different solidification/cooling rates, and by comparisons with the experimental results of quantitative measurements of corresponding solidification microstructures.