| Popis: |
There has been a significant interest in capturing how the damage is initiated and accumulated in polycrystalline Ni-based superalloys while applying thermal and mechanical impact – tensile and creep loading at 800◦C. This is because the turbine component in jet propulsion or power generation these materials applied can experience such environments while in service and need to avoid unexpected degradation and failure causing severe accidents. In situ damage observation techniques required to be developed to understand the sequential mechanisms of damage growth even in such complicated environment. In this work, for the first time in this field, a design and operation of laboratory-scale X-ray computed tomography (XCT) arrangement is developed for the purpose of in situ damage observation. The in situ XCT technique covers high-temperature mechanical testing and improvements of tomography image processing for high resolution enables to capture the sequential damage growth during tensile or creep loading at 800◦C, in examples of polycrystalline Ni-based superalloys, Inconel 718 and Nimonic 80A. Furthermore, laser-based Acoustic Emission (AE) techniques are combined with the system to determine whether the object is damaged to be captured by XCT. The developed in situ observation technique was applied to high-temperature tensile and creep testing. Our results indicated that the damage growth could be captured with the resolution of 30 µm at 800◦C, and can be compared not only with strain rate and loading condition but with the stress state of the deformed testpiece, and that AE the technique can be the damage indicator of the object by observing the change in AE energy and frequency. |
