航空镍基单晶叶片激光制造气膜孔损伤机理及寿命模型研究

Film cooling as an important thermal protection technology has been widely used in gas turbine blades. However, the analysis of turbine blade rapture shows that most of them are caused by the stress concentration due to the cooling holes and the surface quality defects during the process. Based on Laser hole making process, the project pay attention on structural characteristics and service environment for nickel-based single crystal blades. Considering the aspect of surface state, microstructure evolution, macroscopic performance and finite element simulation, the project aims to study the damage mechanism of the cooling holes and life predicted model. For single crystal material, the relationship between process parameters and surface quality, surface quality and macroscopic properties will be concluded to investigate the damage mechanism of cooling holes. Based on the continuous damage mechanics, a damage model considering the Laser processing parameters will be established. Combined with the crystal plasticity theory, a single-crystal film hole lifetime model by coupling Laser processing parameters will be established. In view of the curved surface structure and different arrangement of cooling holes, a finite element life prediction method for cooling holes will be established under complex stress state. Finally, the application of the typical blade will be analyzed and discussed. According to the different size and service environment, laser manufacturing film hole blade processing strategy will be proposed to provide theoretical guidance and technical support for the laser manufacturing film hole processing optimization, and thus improve the life and reliability of the aero engine blade.

气膜冷却作为行之有效的热防护技术广泛的应用于涡轮叶片中，但航空发动机叶片断裂故障分析表明，大部分为气膜孔引起的应力集中及加工过程中的表面质量缺陷造成的。本项目从激光制孔工艺出发，针对镍基单晶叶片的结构特点和服役环境，从表面状态、微观组织演化、宏观性能及有限元模拟等方面研究激光制造气膜孔损伤机理及寿命预测模型。针对单晶材料，总结工艺参数与表面质量、表面质量与宏观性能的关系，研究气膜孔断裂的损伤机理；基于连续损伤力学，建立考虑激光制孔工艺的损伤模型，结合晶体塑性理论，建立耦合激光制孔工艺的单晶气膜孔寿命模型；针对曲面结构及气膜孔排布方式，建立复杂应力状态下的气膜孔有限元寿命预测方法；最终，进行典型叶片的应用分析，针对不同尺寸及服役环境的叶片，提出激光制造气膜孔叶片加工策略，为激光制造气膜孔加工优化提供理论指导及技术支撑，进而提高航空发动机叶片寿命及可靠性。

气膜冷却作为行之有效的热防护技术广泛的应用于涡轮叶片中，但航空发动机叶片断裂故障分析表明，大部分为气膜孔引起的应力集中及加工过程中的表面质量缺陷造成的。目前国内缺乏对激光制孔参数与气膜孔表面质量系统的研究，没有完善的寿命预测模型。. 本项目从激光制孔工艺出发，研究基于激光加工工艺的气膜孔损伤断裂机理、寿命预测模型及考虑结构曲率、气膜孔排布方式的有限元预测方法。研究结果表明：激光制孔参数可以显著影响气膜孔表面质量，提高功率可以降低锥度；提高重复频率，会在下孔形成较大的热影响区。重复频率过大时，热影响区内还会出现裂纹；降低占空比可以降低微孔锥度，获得更好的孔形，但占空比过低会造成下孔的严重缺陷；过度的负离焦会造成上孔周能量密度过低，产生孔周缺陷；气膜孔平板断裂面是由滑移面滑出产生的，每一个断裂面与应力轴的夹角为45°并均有垂直于断裂平面的滑移迹线，断裂平面互相交错，在交错处裂纹是沿滑移迹线方向扩展断裂的；气膜孔弱化了镍基单晶的蠕变寿命及蠕变应变，光滑平板的蠕变寿命为气膜孔试样的2倍，蠕变应变为9倍左右；气膜孔平板试样断裂模式为高温变形致使孔边产生初始裂纹，沿垂直于应力的加载方向扩展。初始裂纹均产生于气膜孔最大损伤分布的区域；高温下镍基单晶合金气膜孔平板的蠕变强度从大到小依次为[111]>[001]>[011]；孔倾角对结构件的疲劳性能有着明显的影响，倾斜孔的孔边存在明显的应力集中，会形成较多的裂纹，严重缩短结构件的疲劳寿命，45º孔周裂纹数较多，30º孔次之，90º孔最少，与疲劳寿命成对应关系；采用改进的节点应力法和临界距离法可以有效地预测气膜孔结构蠕变及疲劳寿命。. 本项目对所得相关结论可以优化激光制孔工艺参数，为优化气膜孔加工策略、科学评估气膜孔质量和准确预测叶片服役寿命提供理论指导及技术支撑，进而提高航空发动机叶片寿命及可靠性。