Effect of Undercooling on Microstructure Evolution in IN718 Superalloy

摘要:

采用复合熔盐净化法进行了IN718高温合金快速凝固研究，获得了250 K的大过冷度，研究了合金深过冷凝固的组织演化过程。结合BCT模型，分析了合金凝固与组织转变机制。结果表明，过冷IN718高温合金的组织形貌受到熔体过冷度大小的影响。在0~250 K过冷度范围内，IN718高温合金凝固组织将发生两次晶粒细化：当0 K≤ΔT<63 K，凝固组织发生了第1次晶粒细化；当63 K≤ΔT<90 K，发生第2次晶粒细化，随着过冷度的增大，凝固组织发生粗化；当90 K≤ΔT<250 K，凝固组织由树枝晶向粒状晶转变，晶粒明显细化，平均晶粒尺寸达到5.5 μm。

Abstract:

The method of molten salt denucleating was applied to study the rapid solidification of IN718 superalloy. The highest undercooling up to 250 K was produced, and the microstructure evolution with undercooling was investigated. Based on the calculations of the dendritic tip radius, the dendrite growth velocity and undercooling, the solidification behavior and structure transition mechanisms were analyzed by adopting BCT dendrite growth model. Result show that the solidification morphologies of the undercooled IN718 superalloy are dependent on the degree of undercooling. Within the achieved undercooling, 0~250 K, the solidification microstructure of IN718 undergoes twice grain refinement. When 0 K≤ΔT＜63 K, it is the first grain refinement; when 63 K≤ΔT＜90 K, with the increasing of undercooling, grain coarsening comes into being; when 90 K≤ΔT＜250 K, it is the second grain refinement, and aforementioned dendritic structure transforms into granular grain with average grain size about 5.5 μm