异形气膜孔对镍基单晶合金蠕变性能的影响

Effect of film cooling holes on creep properties of nickel-based single crystal superalloy

为满足航空发动机涡轮进口温度不断提升的要求,通常采用气膜冷却技术来有效降低叶片壁面温度。然而气膜孔的存在破坏了叶片结构的几何完整性,在离心载荷与热载荷的影响下易发生蠕变断裂。因此开展气膜孔对镍基单晶叶片蠕变性能的研究具有重要意义。通过开展1 000℃/300 MPa下圆柱形、簸箕形和燕尾形3种气膜孔试验件的蠕变试验和有限元仿真,结合微观表征手段研究了气膜孔孔型对DD6单晶高温合金蠕变损伤的影响机理。结果表明:圆柱孔和簸箕孔的平均蠕变寿命相似,较燕尾孔分别提升了17.4%和15.9%。从断口分析可知,含孔板件的蠕变断裂是由于孔边应力集中引起,裂纹主要萌生于孔边位置。扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和有限元仿真表明,塑性变形区与仿真高应力区相对应,且γ′相筏化形貌与应力分布有关,同时应力越高的地方氧化越显著;能谱仪(EDS)对氧化物的分析结果表明氧化物主要分为3层:外层为Ni O和Co O,中间层为Cr、Ni和Ta的混合物,内层为Al_(2)O_(3)。氧化层附近存在γ′相溶解,孔边的塑性变形与γ′相溶解促进了再结晶的形成。

In order to meet the increase of the turbine inlet temperature of advanced aeroengines,film cooling is used to reduce the blade temperature.However,the geometrical integrity of the blade structure is destroyed by the film cooling holes,which makes the turbine blade more susceptible to creep damage around the film cooling holes under the influence of centrifugal and thermal stresses.Therefore,it is important to understand the creep performance of nickel-based single crystal superalloys with film cooling holes.The creep damage mechanism of DD6 single crystal superalloy with the cylindrical,dustpan and dovetail film cooling holes were studied through the creep experiment and finite element simulation at 1 000℃/300 MPa,and the detailed microscopic characterizations were conducted.The results show that the average creep lives of cylindrical and dustpan holes are similar to each other,and are increased by17.4%and 15.9%respectively compared with the dovetail hole.Based on the fracture analysis,stress concentration and oxidation around the hole edge led to cracking first.Combined with Scanning Electron Microscope(SEM),Electron Back-Scattered Diffraction (EBSD) and finite element simulation,the plastic deformation zone obtained by EBSD corresponds to the high stress region obtained by finite element analysis,and the γ′phase rafting morphology and the oxidation is related to the stress distribution.Energy Dispersive Spectrometer (EDS) analysis indicates that oxides can be divided into three layers,i.e.,the outer layer is mainly Ni O and Co O,the middle layer is mainly a mixture of Cr,Ni and Ta oxides,and the inner layer is Al_2O_3.The γ′free layer occurs adjacent to the oxide layer,and the plastic deformation and γ′phase dissolution around the hole edge facilitate recrystallization formation.