Non-destructive analysis is important in terms of improving the reliability of ceramics. In the study, the internal structure of Al 2 O 3 ceramics with artificial pores was observed via optical coherence tomography (OCT). The OCT observation was performed on a surface perpendicular to the tensile surface of the specimen. The spherical pores were successfully observed via OCT. The strength and fracture origin were predicted from the size and position of the observed pores. The lowest predicted strength (which is realized as the strength of the specimen) was in agreement with the bending strength obtained via three-point bending tests. The actual fracture origin observed by scanning electron microscope was also the same as that predicted via the OCT observation. Thus, the results indicated that the nondestructive testing via OCT was useful in terms of predicting the strength and fracture origin of ceramics.
Optical coherence tomography (OCT) is an observation technique utilizing optical interferometry. Images of the internal structure of opaque materials can be obtained dynamically and three-dimensionally in a few seconds. In this work, the internal structures of ceramic sintered body and slurry was observed by OCT. In the case of Al 2 O 3 ceramics, an artificially induced spherical defect having smaller than 50 µm in diameter which lies 700 μm below the top surface was observed successfully. Furthermore, it was observed that the internal structure of Al 2 O 3 slurry was drastically changed during drying, followed by formation of a crack in the dried green body.
In situ observation of sintering of ceramics is important to understand the sintering behavior, including the development of internal structures, and to fabricate ceramics with superior properties. However, there has been no studies thus far on high‐speed in situ observation of the internal structure of green and sintered bodies at high temperatures with micrometer‐scale resolution. Here, we applied swept‐source optical coherence tomography (OCT) to observe the evolution of the internal structure in Al2O3 green bodies during sintering. In situ OCT observations revealed that internal structure changes during sintering, such as the development of density distribution and growth of coarser pores. We could also obtain the sintering shrinkage ratio and relative density from the OCT images. The OCT observation of the internal structure during sintering of green bodies with added or stacked granules of different primary particle sizes confirmed that inhomogeneous regions developed as the densification progressed at high temperatures. These results indicate that in situ observation of the sintering behavior of ceramic green bodies using swept‐source OCT is a novel technique that facilitates real‐time observation of the evolution of the internal structure during sintering.
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