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采用差示扫描量热仪与铜模喷铸技术,研究了较宽冷速(0.17~100 K/s)范围内K424镍基高温合金的近平衡与亚快速凝固行为。利用光学显微镜、扫描电镜及能谱分析仪对不同冷速作用下K424合金的γ基体相、γ′沉淀相、MC碳化物及共晶组织进行了表征,并对平均二次枝晶间距进行了定量分析。结果表明:冷速的提高有效细化了初生γ相,二次枝晶间距由0.17 K/s时的84μm显著下降到100 K/s时的5μm,同时导致γ′沉淀相的析出时间缩短,平均晶粒尺寸下降。亚快速凝固条件下所形成的过饱和固溶体在后续加热过程中发生沉淀相析出。枝晶组织的细化与溶质截留的发生,降低了凝固过程中成分偏析,有利于γ+γ′共晶相及碳化物尺寸的减小。
Near-equilibrium and sub-rapid solidification behavior of K424 Ni-based superalloy with wide cooling rate (0.17 ~ 100 K / s) were investigated by differential scanning calorimeter and copper die casting technology. The γ matrix phase, γ ’precipitated phase, MC carbide and eutectic structure of K424 alloy under different cooling rates were characterized by optical microscope, scanning electron microscope and energy spectrum analyzer, and the average secondary dendrite spacing Quantitative analysis. The results showed that the increase of cooling rate effectively refined the primary γ phase, the secondary dendrite spacing decreased significantly from 84 μm at 0.17 K / s to 5 μm at 100 K / s, and the precipitation time of γ ’precipitates was shortened. Average grain size decreases. The supersaturated solid solution formed under sub-rapid solidification conditions precipitates precipitates during subsequent heating. Dendritic refinement and solute interception occur, reducing the component segregation in the solidification process, is conducive to the γ + γ ’eutectic phase and the reduction of carbide size.