先进单晶高温合金均匀化-固溶热处理的研究与设计

Designing of the Homogenization-Solution Heat Treatment for Advanced Single Crystal Superalloys

摘要:

为设计更适用于先进单晶高温合金的均匀化-固溶热处理制度，研究了不同热处理温度和时间对一种先进单晶高温合金组织的影响。使用金相显微镜和场发射电子显微镜观察合金组织，使用电子探针测试合金元素分布，并分析试验结果。试验发现，当温度直接升至γ′相溶解的实际起始温度1338℃时，合金不会发生初熔；当温度直接升至γ′相溶解的外推初始温度1350℃时，合金中出现了明显初熔，但初熔组织随着保温时间的延长逐渐减少；当温度直接升至较低的1328℃时，合金中虽然没有发生初熔，但均匀化效率明显降低。结合先进单晶高温合金高熔点元素含量较高的特点对试验结果进行热力学和动力学计算与分析，结果表明，单晶高温合金的均匀化-固溶热处理窗口是一个动态的窗口，γ′相完全溶解温度和初熔温度均随着合金均匀化程度的提高而提高；高代单晶高温合金在均匀化-固溶热处理中，不须要将温度始终保持在铸态合金的初熔温度以下，只要保证温度低于合金所在均匀化状态对应的初熔温度即可；均匀化-固溶热处理中，提高每一台阶的温度可以得到的均匀化-固溶效果远优于延长热处理时间可达到的效果。根据试验及分析结果提出了一种适用于先进单晶高温合金的均匀化-固溶热处理制度设计方法，使试验合金在较短时间内得到了理想的合金组织和均匀化效果。

Abstract:

To design more efficient homogenization-solution heat treatments for advanced single crystal superalloys, an experimental single crystal superalloy was studied after homogenization-solution heat treatments with different temperatures and durations. Metallographic and field emission microscope were used to observe microstructures; electron probe was applied for component analysis. The results show that no incipient melting appears when the alloy is directly heated up to 1338℃; when it is directly heated up to 1350℃, obvious incipient melting occurs, while the incipient melting microstructure gradually fades away with holding time; for an lower temperature 1328℃, although there is no risk of incipient melting, the homogenization-solution efficiency is far from satisfactory. After analyzing the results by aid of dynamics and thermodynamics calculation, it can be concluded that the single crystal superalloy owns a dynamic homogenization-solution heat treatment window: both the γ′ solvus end temperature and the incipient melting temperature increase with the homogenization process. Such dynamic characteristic is especially noticeable for advanced single crystal superalloys since the segregation is more severe. There is no need to always keep the homogenization-solution heat treatment temperature below the incipient melting temperature of the as-cast condition, but keeping it below the incipient melting temperature of the alloy at the temporal homogenous state is necessary. For advanced single crystal superalloys, elevating temperatures of each step is much more effective than prolonging duration to get better heterogeneous effect. By using above conclusions, a new approach is introduced to design effective homogenization-solution heat treatments for advanced single crystal superalloys, and it has been successfully used on the experimental single crystal superalloy.