基于制孔工艺的镍基单晶叶片气膜孔裂纹机理与寿命模型研究

The film cooling technology is an important approach to improve the gas inlet temperature of aero-engine turbine. However, the film holes will also destroy the structural integrity of the turbine blades, and serously affect the strength and life of the turbine blades. The film hole cracks occured frequently in domestic in-service and research aero-engine. The preject intends to study the crack nucleation, propagation mechanism of film holes and life prediction model of nickel-based single crystal blade, taking into consideration of different drilling technique and multi-hole interference. Based on single crystal blade, the original surface characteristics of film holes will be analyzed, considering laser drilling, electrical discharge machining and electro-stream machining technique. The mechanical experiments of thermal-mechanical fatigue-creep with temperature gradient will be carried out, in order to get the relation between the hole surface characteristics and macro-response. Combined with in-situ obersevation and molecular dynamics, crystal plasticity theory et al, the crack nucleation and propagation mechanism of hole surface will be studied. Aiming to thin-walled curved structure, multi-hole interference meso-mechanism and theory will be studied. Finally, the life model for nickel-based single crystal cooling blade will be established, and the finite element user subroutines are developed subsequently.The life model will be used to analyzed the life of a real nickel-based single crystal turbine blade. The project research is scientifically important with great engineering significance for fully usage of the material potential and endurance of the structural safety during the design-life time.

气膜冷却是提高航空发动机涡轮前燃气进口温度的重要技术途径，但是气膜孔破坏叶片的结构完整性，严重影响其强度、寿命，我国在役和在研的航发都出现过气膜孔处开裂的故障。 本项目针对镍基单晶冷却叶片及其服役环境，研究基于制孔工艺和多孔干涉效应的气膜孔裂纹机理及寿命预测模型。针对单晶叶片，获得激光、电火花、电液束三种制孔工艺下气膜孔表面状态的特征描述；开展带温度梯度的热机械疲劳蠕变研究，建立气膜孔表面状态与宏观响应的关系；结合原位观察和分子动力学、晶体塑性等理论模拟，揭示气膜孔孔边裂纹形核机理及扩展规律；针对薄壁曲面结构型式，得到气膜孔的多孔干涉效应的细观机理和理论；最终，基于晶体塑性理论，建立寿命预测模型，开发相应的有限元子程序，进行典型叶片应用研究。本项目对于充分发挥材料的性能储备和确保叶片在设计寿命期内不发生破坏事故具有重大科学和工程意义。

气膜冷却是提高航空发动机涡轮前燃气进口温度的重要技术途径，但是气膜孔破坏叶片的结构完整性，严重影响其强度、寿命，我国在役和在研的航发都出现过气膜孔处开裂的故障，目前国内外缺乏合理、准确的单晶叶片气膜孔裂纹机理和寿命评估模型。.本项目主要研究内容为针对单晶叶片，研究激光、电火花、电液束三种制孔工艺下气膜孔表面状态特征，建立气膜孔表面状态与宏观响应的关系；分析气膜孔孔边裂纹形核机理及扩展规律；研究得到气膜孔的多孔干涉效应的细观机理和理论；基于晶体塑性理论，建立寿命预测模型并进行典型叶片应用研究。.研究结果表明：激光制孔再铸层较厚（50μm）、存在较多微裂纹，效率较高；电火花制孔再铸层相对较薄（20μm），存在少量微裂纹；电液束制孔无再铸层，再铸层、微裂纹、表面粗糙度是气膜孔表面状态特征的三个重要方面。气膜孔存在显著的多孔干涉效应，当孔间距不变时，随着孔径的减小，最大Mises应力减小，多孔干涉效应逐渐减弱；当孔径不变时，随着孔间距的增大，最大Mises应力减小，多孔干涉效应减弱。建立了电火花、激光、电液束三种制孔工艺下气膜孔单晶结构强度寿命评估方法。气膜孔单晶结构寿命预测结果与试验数据对比最大误差在2倍分散带之内。.本项目对于充分发挥材料的性能储备和确保叶片在设计寿命期内不发生破坏事故具有重大科学和工程意义。本项目的研究成果应用到具体单晶叶片寿命分析之中，可以提供相应的分析工具与手段，不仅能够尽量避免灾难性事故的发生，减少不确定因素，而且可为充分利用叶片性能储备和安全地确定单晶冷却叶片寿命，从而推动国产发动机的发展，同时为制定适合叶片不同部位的制孔工艺提供有用的信息。