应用液态金属冷却(LMC)和高速凝固(HRS)定向凝固技术, 对DZ125高温合金叶片状铸件在不同抽拉速率下的组织演变规律进行了研究,并对比研究了LMC和HRS法所得铸件的微观组织. 结果表明, 同一定向凝固方法下, 随抽拉速率的提高, 铸件枝晶组织及γ'析出相得到细化; 应用LMC技术所制备铸件的枝晶组织和γ'析出相较相同抽拉速率HRS方法时更为细小; 相同工艺参数下LMC和HRS方法所制备铸件一次枝晶间距的差异随铸件壁厚及抽拉速率的增大而更显著. 通过对固/液界面前沿温度梯度进行估算发现, LMC方法可获得更高的温度梯度, 且其温度梯度受抽拉速率变化影响较HRS更小. 除70 μm/s抽拉速率外, LMC法所得γ+γ'共晶组织的含量均显著少于HRS方法; 70 μm/s抽拉速率时, LMC法产生的偏析较严重, 而其余凝固条件下偏析程度较相同工艺参数下HRS轻. 110 μm/s抽拉速率时, HRS方法较LMC方法制备铸件中MC型碳化物尺寸更大.
As a precipitation hardened unidirectionally solidified Ni-based superalloy, DZ125 has been widely applied as structure materials in advanced aeroengine for gas turbine blades and vanes. In present, the paper on the influence of solidification parameters on microstructures have been largely published, but unfortunately, few of them have focused on giving a direct comparison between directional solidification characteristics in liquid metal cooling (LMC) and high rate solidification (HRS). In this paper, the influences of processing parameters on microstructures of blade shaped castings prepared both by LMC and HRS technique were studied. The results show that the dendrite structure and γ' precipitate in castings prepared by the same method are refined with elevated withdrawal rate; in the same solidification conditions, the LMC castings have finer dendrite structure and γ' precipitate than HRS, the larger the disparity between primary dendrite arm spacings in LMC and HRS castings, the thicker wall thickness is or the higher the withdrawal rate is. It is found that higher temperature gradient in front of solid/liquid interface can be obtained by LMC, and its variation with elevated withdrawal rate, however, is smaller than that by HRS. The γ+γ eutectic fraction is lower for LMC castings than HRS castings except for withdrawal rate of 70 μm/s, only at which more severe segregation than HRS's occurs. Chinese script type MC flakes between dendrites in HRS castings are larger at withdrawal rate of 110 μm/s.
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