An automated three-dimensional internal structure observation system based on high-speed serial sectioning of steel materials

► We developed 3D internal structure observation system based on serial sectioning. ► This system incorporates ultrasonic vibration cutting device and optical microscope. ► This system permits automated serial sectioning with high-speed of 1 min/slice. ► 3D shapes of Inclusions in bearing steel were observed from 400 sectional images. For three-dimensional observation of the internal structure of hard materials, we developed an automated system based on serial sectioning with precision cutting and optical microscopy. The elliptical vibration cutting device in the system created mirrored surfaces suitable for optical microscopy during the serial sectioning of steel materials. In this study, high-speed sectioning with several micron thickness and repeated precise machining to depths of up to around 1mm were achieved with a flat-edge cutting tool. For a 3mm×3mm area of bearing steel, a mirrored surface could be created in about 1min, and 400 serial sectioning images were obtained within 7h without additional machining processes such as cleaning or changing of tools. The three-dimensional shapes and positions of continuously distributed inclusions found deep within the bearing steels, as well as cracks originating from these inclusions, could be detected with resolutions as high as 80nm×80nm and in a wide field of view using this system.