【摘要】 DD10是一种新型的镍基单晶高温合金，针对其母合金易出现微观偏析等凝固缺陷问题，本文运用Thermo-Calc热力学软件以及微观偏析模型计算冷却速度对微观偏析的影响规律，并利用光学显微镜（OM）、电子探针（EPMA）等实验方法研究浇注温度对DD10母合金微观偏析和碳化物的影响机制。微观偏析模型计算结果表明，随着冷却速度的增大，微观偏析减弱。结果表明，DD10母合金的显微组织为典型的树枝晶，随着浇注温度的降低其二次枝晶间距减小，冷却速度增大；母合金的微观偏析随浇注温度的降低呈现先减弱后增强的趋势。此外，随着浇注温度的降低，碳化物的析出量和尺寸先降低后增大，而碳化物的数量持续降低。因为微观偏析程度受二次枝晶间距和液相流动性的共同影响，在适当的浇注温度时，合金的二次枝晶间距适中，液相流动性也较好，故而微观偏析程度较轻；碳化物的析出过程主要受微观偏析和二次枝晶间距的影响，微观偏析越严重，碳化物析出量越多，而二次枝晶距越小越有利于生成大尺寸长条形碳化物。因此，浇注温度过高易导致大尺寸块状碳化物生成，浇注温度过低则有利于生成大尺寸长条形碳化物。更多还原

【Abstract】 The elevated alloy content in superalloy master alloys results in significant microsegregation during the solidification process, potentially giving rise to the formation of sizable carbides and brittle eutectic phase. Nonetheless, eliminating the brittle phase from the master alloy of single-crystal superalloys during subsequent directional solidification is challenging, as it tends to be retained and can significantly degrade the product′s performance, particularly in turbine blades. To address the challenge of microsegregation and other solidification defects in superalloys, an investigation into the impact of pouring temperature on microsegregation and carbide precipitation in DD10（nickel-base single crystal superalloy） master alloy was conducted. Aiming to address the susceptibility of superalloys to solidification defects, such as microsegregation, a 1.3 kg DD10 master alloy ingot was produced in a laboratory vacuum induction furnace.Subsequently, a small sample was extracted from the ingot for analysis. Following grinding and polishing of the sample, scanning electron microscope（SEM） and energy dispersive X-ray spectroscopy（EDS） techniques were employed to observe and analyze the carbides present. Additionally, the sample underwent corrosion treatment using a microetching solution（comprising 76.45% HCl, 7.21% H₂SO₄ and 16.34% CuSO₄）. Optical microscopy was utilized to examine the alloy′s microstructure. Further analysis was conducted with electron probe microanalysis（EPMA）, involving both surface scanning and point scanning of the samples at various pouring temperature to assess microsegregation within the ingot. The equilibrium distribution coefficient of alloying elements in superalloy DD10 was determined using the equilibrium module within the Thermo-Calc thermodynamic software. To comprehensively investigate the impact of cooling rate on microsegregation, it was considered in conjunction with the microsegregation model. The results indicated that DD10 master alloy exhibited a characteristic dendritic microstructure. As the pouring temperature decreased, secondary dendrite spacing decreased while the cooling rate increased. Al, Ta, and Ti exhibited positive segregation between dendrites, while Co, Cr, and W showed negative segregation within the dendrite core. Mo, on the other hand, exhibited relatively uniform distribution without a noticeable segregation tendency.The segregation of Ti, Ta, and W was particularly pronounced. As the pouring temperature decreased, the segregation of alloy elements initially decreased and then increased, with the lowest segregation observed at 1380 ℃. Significant improvement in the segregation of Ti, W, Cr, and Co was observed at a pouring temperature of 1380 ℃. Thermo-Calc thermodynamic software calculated the liquidus temperature of the DD10 master alloy during equilibrium solidification to be approximately 1341 ℃, with a solidus temperature of about 1293 ℃. During solidification, the γ phase precipitated initially, followed by the precipitation of MC carbides. At 1172 ℃, following solidification, the γ phase underwent a transformation known as γ′. Results from the microsegregation model calculations indicated that as the cooling rate increased, the concentrations of positive segregation elements Ti and Ta in the interdendritic regions decreased, while the concentrations of negative segregation elements W in the same regions increased, resulting in a weakening of microsegregation in the alloy. Nonetheless, the extent of microsegregation was influenced by secondary dendrite spacing and liquid fluidity. At a pouring temperature of 1380 ℃, the alloy exhibited a moderate secondary dendrite spacing, coupled with good liquid phase fluidity, resulting in the least degree of microsegregation. The findings revealed that carbides within the DD10 master alloy were predominantly located in the interdendritic regions. At a pouring temperature of 1360 ℃, numerous large-scale strip carbides, characterized by their richness in Ti and Ta（referred to as MC carbides）, were observed. However, at temperatures of 1380 ℃ and 1400 ℃, predominantly massive carbides were present. Bulk carbides were categorized as either composite or pure carbides. Composite carbides primarily consisted of Ti（C, N） at the core, with peripheral carbides comprising MC carbides rich in Ti and Ta. Similarly, pure carbides also consisted of MC carbides rich in Ti and Ta. The size and area ratio of MC carbides exhibited an initial decrease followed by an increase with rising pouring temperature.At a pouring temperature of 1380 ℃, the MC carbides attained their minimum size, with an average size of 7.27 μm. Conversely, at 1360 ℃, the carbides reached their maximum size, averaging 10.28 μm. The average carbide size was 7.86 μm at 1400 ℃. As the pouring temperature decreased, the quantity of carbides diminished. This phenomenon was primarily associated with microsegregation and secondary dendrite spacing. Greater microsegregation resulted in more carbide precipitation, while smaller secondary dendrite spacing facilitated the formation of large-size long strip carbides. The formation of large-size massive carbides at higher pouring temperature and large-size strip carbides at lower pouring temperature adversely impacted the alloy′s properties. In conclusion, when the pouring temperature was 1380 ℃, the microsegregation of the master alloy was at its minimum, while the precipitation amount and carbide size were optimized. Consequently, selecting the appropriate pouring temperature enhanced the reduction of microsegregation and optimized carbide formation in the master alloy.更多还原