高温合金单晶叶片定向凝固过程的宏微观数值模拟

基于有限元和Panda热动力学数据库建立了单晶叶片真空熔模铸造定向凝固过程的数理模型，对不同工艺下单晶叶片试样凝固过程中的温度场、糊状区演变及枝晶二次臂间距进行了仿真，研究了缺陷形成机理和规律。计算结果与实验吻合良好。计算结果显示，拉速大时二次臂细小，但杂晶产生的趋势加大；拉速小时杂晶不易形成，但二次臂增粗。对实际空心薄壁复杂单晶叶片定向凝固过程的模拟研究表明，二次臂间距在叶身部分分布比较均一， 3.5 mm/min抽拉时有可能在缘板处产生杂晶。采用变拉速工艺，不仅可避免杂晶缺陷，还能保证工件大部分枝晶细小，提高生产效率和成品率

Macro and Micro Numerical Simulation of Directional Solidification of Super Alloy SX Turbine Blade

Defect-free blades with fine microstructure and excellent high temperature performance are needed by aero-turbine. The curved shape of SX (single grain) blade is usually very complicated, and its section varies sharply at the platform, the tip shroud, etc. Thus, stray grains are difficult to avoid during directional solidification. In order to optimize the process parameter, the physical model and the mathematical model of directional solidification of SX blade were established based on Panda thermodynamic database and finite element. The temperature field, the evolution of mushy zone and the SDAS (secondary dendrite arm spacing) during solidification of SX sample by different process were simulated, and the discipline and mechanism of defect formation were investigated. The numerical results agree well with the experimental. The calculated results indicate that with the higher withdrawal rate, the SDAS gets smaller but stray grains tend to occur; with the lower withdrawal rate, the possibility of stray grains gets lower but the SDAS gets larger. The directional solidification of complicated thin-walled hollow real SX blade was simulated as well. The results show that the SDAS is nearly uniform in the blade, stray grains may appear at the platform when the withdrawal rate is up to 3.5 mm/min. By the process with varying withdrawal rate, the stray grain can be avoided while most of secondary dendrite can be refined, thus improving the productivity and percent of pass