镍基单晶高温合金DD6气膜孔热机械疲劳试验

涡轮冷却叶片气膜孔边存在大应力梯度，且服役时承受交变的机械载荷和热载荷，热机械疲劳（TMF）是其主要失效模式。通过开展带气膜孔和不带气膜孔的薄壁圆管试件TMF试验研究了气膜孔对镍基单晶高温合金TMF寿命的影响。结果表明最大循环应力在300~500 MPa应力范围内，循环应力幅值与镍基单晶高温合金TMF寿命呈现良好的对数线性关系，且气膜孔导致镍基单晶高温合金TMF寿命下降可达82.5%。继而完成了横向取向分别为〈010〉、〈110〉方向的气膜孔模拟件试验，结果表明气膜孔取向为〈110〉时寿命最短，仅为〈010〉取向的40.0%。最后开展了不同制孔工艺下的气膜孔模拟件试验，结果表明激光制孔气膜孔模拟试件寿命仅为电液束制孔气膜孔模拟试件的54.0%。气膜孔模拟件断口分析表明:TMF裂纹均萌生于气膜孔边，源区氧化严重；裂纹沿着大致与气膜孔边垂直的方向扩展。 

Thermomechanical fatigue on the nickel based single crystal superalloy DD6 with film cooling hole

Turbine blades are subjected to thermal loads and mechanical loads simultaneously occurring during operation. Thermomechanical fatigue (TMF) is a major life-limiting factor for turbine blades. Film cooling holes within the blade introduced substantial stress concentration, which could dramatically reduce the lifetime. For quantification purposes, both smooth tubular specimens and notched specimens were utilized to perform TMF experiments. Results indicated that stress and fatigue life were in a good logarithmic linear correlation when the maximum stress changes within the range of 300-500 MPa and the hole could reduce the TMF life by 82.5%. Notched specimens with 〈010〉 and 〈110〉 oriented hole were tested respectively. It was found that the hole in 〈110〉 orientation had the weakest anti-TMF ability, since its life was only 40.0% of the 〈010〉 oriented notched specimen. The effect of drilling process was also studied. The results revealed that the life of notched specimen drilled by laser was 54.0% of the notched specimen drilled by electro-streaming drilling. The crack morphology demonstrated that TMF crack initiated from the film cooling hole edge which was severely oxidized and the crack propagated along the direction perpendicular to the edge of the hole.