Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Ni-based single crystal (SX) superalloys are widely used for production of blades in gas turbines and aircraft engines for their superior mechanical performance at high temperatures. To obtain high cooling efficiency, most of the SX blades consist of thin wall with cooling holes. However, thermal fatigue cracks are usually observed in blades with this kind of structures. Thus, it must be valuable to investigate the crack initiation and propagation around a hole during thermal fatigue tests in a SX superalloy. In the present work a second generation SX Ni-based superalloy was used. Plate specimens that parallel to directional solidification (DS) direction and along (100) or (110) planes were prepared. A hole with diameter of 0.5 mm was drilled vertical to the surface in the middle of the plate by electro-discharge machining (EDM). Thermal fatigue tests were performed between room temperature and 1100 ℃. Effect of crystal orientation on the crack initiation and propagation was investigated and the reasons were analyzed. It was found that a thin recast layer was produced around holes of EDM drilled. The thickness of the recast layer was 15 mm in the maximum. Crystal orientation has great effect on the crack initiation sites and propagation kinetics. After 80 cyc thermal fatigue tests, in (110) specimens cracks initiated at the edge of the holes that vertical to the DS direction, then grew quickly and propagated along directions about 45° from the DS direction. After 200 cyc tests, cracks developed to more than 2 mm in length. While in (100) specimens no cracks could be observed even after 200 cyc thermal fatigue tests. This difference was mainly due to the combined effects of different thermal stress caused by the anisotropy of single crystals and of the microstructure characteristics.
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