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

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.

Key words:single crystal superalloy; homogenization; solution; heat treatment