Effect of Directional Solidification Methods on the Cast Microstructure and Grain Orientation of Blade Shaped DZ125 Superalloy

摘要:

对应用液态金属冷却(LMC)和高速凝固(HRS)方法制备的叶片状高温合金铸件的铸态组织进行了研究，以比较2种定向凝固方法的优缺点。分别对沿铸件凝固方向不同截面位置处的晶粒取向、一次枝晶间距和γ′ 相尺寸进行了分析。结果表明，对于HRS铸件的中部截面，枝晶的<001>方向偏离铸件轴向的最大角度在抽拉速率由40 μm/s提高至110 μm/s的过程中不断减小。在70 μm/s的抽拉速度下，LMC铸件中部截面处的中心区域内晶粒的最大偏离角度要大于HRS铸件的相应位置处的偏离角，但是晶粒的整体取向却呈现较HRS铸件更集中的趋势。铸件顶部截面处的枝晶组织比中部截面处要粗大，这种现象在HRS铸件中更严重。γ′ 相尺寸在铸件由叶身位置凝固至平台位置的过程中不断粗化。但当抽拉速率高于70 μm/s时，叶身位置和平台位置之间γ′ 相尺寸之间的差异在LMC铸件中更小

Abstract:

The cast structures of blade-shaped castings of DZ125 superalloy processed by liquid metal cooling (LMC) and high rate solidification (HRS) methods were studied to compare the benefits and drawbacks of these two methods. The morphologies and the growth direction of grains, primary dendrite arm spacing, γ′ size were analyzed at different cross-sections along growth directions. The results indicate that the maximum deviation angle of primary dendrites from the sample axial decreases as the withdrawal rate increases from 40 to 110 μm/s for the central zone of HRS castings. At the withdrawal rate of 70 μm/s, the grains in the central zone of LMC casting have larger deviated angles, but the overall orientations of grains become more converging. The dendrites at the top of the blade are coarser than those at the middle, especially for the HRS castings. The γ′ size becomes larger as castings solidify from the airfoil to the platform, but the difference of γ′ size between the platform and the airfoil is smaller for LMC castings when the withdrawal rate is higher than 70 μm/s.