Prediction of strength based on defect analysis in Al₂O₃ ceramics via non-destructive and three-dimensional observation using optical coherence tomography

Abstract

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.

Control of the particle-assembled structure and a novel evaluation technique for high-performance ceramics

“…Based on these results, OCT observation was applied for the nondestructive inspection of the Al 2 O 3 ceramics. 38) Although the details are omitted in this review, the predicted mechanical strength and the morphology and position of the defect as the origin of fractures detected by OCT observation showed good agreements with the strength obtained from a three-point bending test and the SEM observation.…”

In situ observation of evolution of internal structure of alumina during sintering by swept‐source OCT

“…In the infrared transmission image, bright spots with sizes of several tens of micrometers were also observed. According to our previous reports, the bright pairs in the OCT images originate from the reflections at the upper and lower surfaces of the pore 23,24 . Although SEM observations of the same positions are not available in this study, it is suggested that there are large pores in the Al 2 O 3 ceramics that grew during sintering.…”

“…As described above, swept-source OCT has the necessary features for in situ observation of evolution of the internal structure of green bodies during sintering. Previously, we reported static observations of the internal structure of green bodies and ceramics with artificial defects using swept-source OCT. 23,24 These reports clarify the physical meaning of the raw OCT images of the green body and ceramics by comparing them with images obtained by infrared microscopy, X-ray CT, and ultrasonic microscopy. Other static observations of the internal structure of ceramics using OCT have also been reported.…”

“…We have been employing optical coherence tomography (OCT) to observe the internal structure of ceramics 23,24 . OCT is a nondestructive observation method based on optical interferometry 25–27 .…”

“…We have been employing optical coherence tomography (OCT) to observe the internal structure of ceramics. 23,24 OCT is a nondestructive observation method based on optical interferometry. [25][26][27] Moreover, a relatively new OCT system, swept-source OCT, was initially applied to a commercially available apparatus for imaging the choroid and sclera at the back of the retina in 2012.…”