Grain growth and defect control strategy of large module single crystal superalloy turbine blades

Abstract:

With the promotion and application of new large-sized single crystal superalloy turbine blades with complex air-cooled structures in aviation engines, the demand for single crystal turbine blades has sharply increased, leading to the prominent problem of cost reduction and efficiency improvement of single crystal turbine blades. At present, the growth and defect control technology of large module single crystal superalloy blades is one of the effective ways to reduce costs and increase efficiently of single crystal blades, and it is also an important development direction for the production technology of new single crystal turbine blades. Therefore, combining numerical simulation and experimental verification, the directional solidification process of single crystal superalloy turbine blades with different size modules will be studied to explore the behavior of single crystal growth, the formation law of stray grain, and corresponding control methods. The results show that during the directional solidification process, the liquid isotherm presents an "upward convex" shape, which leads to the inner side of the platform reaching the nucleation condition first, inducing the formation of stray grains in the platform. As the withdrawal rate and module size increase, the degree of "upward convex" of the liquid isotherm will significantly intensify, leading to an increased probability of stray grain formation. By adding graphite regenerator at the center of the module, the uniformity of the temperature field can be effectively improved and the inclination degree of the isotherm can be decreased, which can significantly reduce the probability of stray grain formation and improve blade qualification rate, thereby the problem of cost reduction and efficiency improvement for single crystal blades can be solved.