大模组涡轮叶片单晶生长规律与杂晶缺陷控制策略

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

摘要:

随着具有复杂气冷通道的新型单晶高温合金涡轮叶片在航空发动机上的推广应用,单晶涡轮叶片的需求量急剧增加,导致单晶叶片降本增效的需求越来越迫切。而大模组单晶叶片铸造技术是实现其降本增效的有效途径之一,也是单晶涡轮叶片制备技术的重要发展方向。因此,本文采用数值模拟和实验验证相结合的方法,研究了不同尺寸模组叶片的单晶生长行为、杂晶缺陷形成规律以及相应的控制方法。结果表明,单晶涡轮叶片生长过程中,液相等温线呈现“上凸”形状,导致叶片缘板内侧率先达到形核条件,诱发缘板杂晶形成。随着抽拉速率和模组尺寸的增加,液相等温线“上凸”的程度会显著加剧,进而增加叶片杂晶缺陷的形成几率。通过在模组中心位置增加石墨蓄热体,可有效提高温度场均匀性,减小等温线倾斜角度,显著降低杂晶缺陷的形成几率,提高叶片合格率,解决单晶叶片降本增效问题。

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.