不同模组结构高效制备单晶叶片定向凝固过程的温度场及组织模拟

Temperature field and microstructure simulation of directional solidification process of single crystal blade prepared efficiently with different module structures

摘要:

针对18个单晶高温合金叶片高效制备过程中温度场不均匀而导致的杂晶缺陷问题，设计了三种不同的单晶叶片模组结构，采用ProCast软件和CAFE模块对第二代单晶高温合金DD6不同模组结构在高速凝固工艺下的温度场和晶粒组织进行模拟研究，分析了不同模组结构下叶片的温度场演化和抽拉速率对杂晶的影响。结果表明，单层模组由于中柱的保温作用较小，导致叶片近中柱侧的散热效率高于近炉壁侧，凝固过程固液界面弯曲严重，凝固过冷大，杂晶形成倾向大；通过对单层模组添加套筒，以加强保温作用，可有效改善温度场，减小固液界面弯曲程度，避免杂晶形核；而双层叠加模组温度场分布均匀，凝固过冷小，杂晶形成倾向小。套筒模组和双层叠加模组在抽拉速率小于100 μm/s时均无杂晶形成，但双层叠加模组将模组直径缩小为其余两种模组结构的一半，降低了对炉体型腔尺寸的要求，有望实现单晶叶片的高效制备。

Abstract:

For the stray grain problem of 18 single crystal blades in high efficiency preparation due to the non-uniform temperature field, three different module structures ensure to have same production capacity were designed. The high rate solidification of DD6 Ni-based superalloy under different module structures was simulated by using ProCast software and CAFE model, the influence of the temperature field evolution and the withdrawal rate on stray grains was analyzed. The result showed that the solid-liquid interface of the single-layer module became curved seriously because the cooling efficiency of side close to the center pillar is higher than the side close to the furnace body for the heat preservation effect of center pillar is weak, and it had a large undercooling and tendency to form stray grains. By adding a sleeve to the single-layer module to increase the heat preservation effect, the temperature field can be changed effectively, the degree of bending was reduced to avoid the nucleation of stray grain. The double-layer superimposed module had a uniform thermal and a low undercooling, which could decrease the tendency of stray grain effectively. Both the double-layer superimposed module and the sleeve module could form a complete single crystal when the withdrawal rate was below 100 μm/s, however the diameter of the double-layer superimposed module reduces to a half of the other two, which could reduce the requirement of size of furnace body, it could achieve efficient preparation of single crystal blades.