应力对第3代单晶高温合金超高温蠕变断裂机制的影响

Stress Effect on Rupture Mechanisms of a Third Generation Single Crystal Superalloy Crept at Ultra-High Temperature

对第3代单晶高温合金DD33进行了1150℃,80~150 MPa的蠕变测试,借助SEM、EBSD、EDS和TEM研究了不同应力下蠕变断口形貌和截面损伤特征,分析了应力对蠕变断裂机制的影响。结果表明,不同应力条件下近断口铸孔普遍发生多面体化且沿端角开裂,与低应力条件相比,150 MPa下可观察到较多蠕变孔及其诱发的裂纹。80 MPa下,由于长时间暴露,样品表面产生较厚的氧化影响区,使有效应力提高了35 MPa;断口附近局部可见TCP相,并在其与γ′相界面产生较多孔洞和裂纹。随着应力进一步增加,深入基体的表层裂纹增多,更多碳化物开裂,但组织中未发现TCP相。因此,不同应力下合金的最终断裂除了与内部孔洞开裂、彼此联结直接相关外,还应考虑氧化影响区、深入基体内部的表层裂纹、TCP/γ′界面裂纹以及开裂碳化物的贡献。

Creep tests at 1150℃,80-150 MPa were carried out in a 3rd generation single crystal superalloy DD33.The fracture morphology and damage characteristics in longitudinal section were studied by SEM,EBSD,EDS and TEM.The effect of stress on the fracture mechanisms was analyzed.The results show that the casting pores near the fracture are almost polyhedral,and cracks initiated at the corner of pores.Compared with the lower stress,more creep pores and cracks were induced at 150 MPa.Besides,at 80 MPa,theγ/γ’matrix bears an extra 35 MPa effective stress due to the thick oxidation affected zone.The highly-localized topologically close-packed(TCP)phase can be found nearby the fracture,and some pores as well as cracks exist at TCP/γ’interface.With the further increase of applied stress,more surface cracks penetrate into the matrix and more carbides are cracked.Thus,the final failure of the alloy not only directly relates to the internal pores and the pore-induced cracks,but also the effect of the oxidation affected zone,surface cracks penetrating into the matrix,cracks at TCP/γ’interface and cracked carbides should be considered.