Understanding the formation and evolution of low-angle grain boundaries in Nickel-Based single crystal superalloys

Abstract

Grain boundaries have long been of utmost importance in the research and application of single-crystal superalloys. However, there are still many unsolved mysteries regarding the understanding of grain boundaries throughout the solidification process. The work focuses on investigating the formation, the evolution, and the disappearance of low-angle grain boundaries, including subgrain boundaries. The findings show that the low-angle grain boundaries and subgrain boundaries in various dendritic arrays exhibit morphological variances and different development processes. The subgrain boundaries in the aligned array appear to be straight, where irregularly fine-grained γ' precipitates have formed. In contrast, low-angle grain boundaries show a curved and sawtooth-like structure in misaligned arrays. The γ' precipitates locating in the region are regularly long strips. The generation of grain boundaries is a result of the adjustment in dendritic spacing, where the influence of solute leads to dendrite deflection. The misorientation of grain boundary is constantly changing in response to dynamic changes in dendrite spacing. The low-angle grain boundaries eventually dissolve as the dendritic array evolves. This study enriches understanding of the interplay between dendrite arrays and grain boundaries, offering theoretical insights into the evolutionary patterns of grain boundaries within single-crystal superalloys.