A thermal uniformity-based downward directional solidification technology for controlling the hysteresis effect during solidification of single-crystal turbine blades

The hysteresis effect is an essential characteristic that arises during the directional solidification of single crystal (SC) castings when using traditional processes that employ circular molds and drum-shaped heating and cooling systems. This effect is primarily responsible for the formation of freckles and stray grain defects in the SC castings, contributing to a high rejection rate. To effectively control the hysteresis effect, this paper proposes a novel thermal uniformity-based downward directional solidification (TUDWDS) technology. This process is systematically compared with a conventional high-rate solidification (HRS) process in terms of controlling freckle and stray grain defects, validating its capability to manage the hysteresis effect through both experimental and simulation methods. The results indicate that the TUDWDS process completely eliminates freckles by preventing longitudinal solute convection due to its solidification mode aligning with gravity. Additionally, its parallel heating and cooling systems provide a more uniformly distributed temperature field compared to the HRS process, significantly reducing stray grains in SC castings. These findings suggest that the TUDWDS process exhibits a strong capability to control the hysteresis effect. Moreover, the novel process facilitates stronger heat transfer directions, which enhances the overall heat exchange effect and thermal gradients during the directional solidification, further mitigating the defects associated with lower thermal gradients. Therefore, this process shows promising potential for widespread use in the industrial production of SC castings.