Recently, opportunities for the utilization of X-ray tomography techniques in industry and scientific research are increasing. These techniques are applied in various ways for the assessment of the performance, quality, reliability, dimensions, and inner morphology of casting products. However, the lack of fundamental knowledge and understanding for these applications have sometimes led to the unsuccessful use of X-ray tomography techniques in industry. With this in mind, the fundamentals of two important keywords, spatial resolution and contrast, are described in detail in this paper in order to arouse the attention of readers on the importance of these two issues to effectively utilize X-ray tomography. This review was written for foundry engineers in the industry on quality assurance, development and component design relating to various casting defects of aluminum and cast iron castings, as well as engineers/researchers involved in the development and research of cast materials and cast components. In this sense, it intends to introduce various examples of objects of observations such as casting defects and component design. Finally, new functions of X-ray tomography techniques for in-line inspection devices and coordinate measuring machines are described to open up new possibilities in industry.

  Image-based finite element (FE) simulation, based on images of a model built with 3D images obtained by synchrotron radiation nano-tomography, was performed to investigate the point of preferential damage on Si particles in the early stage of tensile deformation in Al-10%Si casting alloys. By reproducing stress concentration on Si particles with the FE simulation, the effects of particle parameters such as (1) particle size, (2) particle orientation to loading direction, and (3) particle shape on damage were evaluated. Nano-tomography observation suggested that the parameters influence damage. The increasing rate of maximum hydrostatic stress differed depending on the Si particle size. Larger particles showed rapid increment in stress, suggesting that preferential damage may occur in large particles at an early stage of tensile deformation. In the study on the influence of particle orientation, particles whose longitudinal direction are more or less parallel to the tensile direction tend to also show rapid increment in stress. However, the most rapid development of the maximum hydrostatic stress was observed in particles possessing small Gaussian curvature which corresponds to severe necking. Comparisons of particles having specific parameters with damaging behavior revealed that the most influential parameter of particles on stress concentration was particle shape possessing necking.

  The morphologies of various abnormal graphite can be observed in heavy-section spheroidal graphite cast iron, which are not found in thin-section spheroidal graphite cast iron. For example, chunky graphite that crystallizes as the eutectic solidification time becomes longer is a typical abnormal graphite structure, and it is known to reduce the fatigue strength, tensile strength, and elongation in spheroidal graphite cast iron. Papers on anomalous graphite have been reported, in many cases observing two-dimensional cross-sections with an optical microscope, but few reports have focused on the overall three-dimensional structure. In this study, heavy-section graphite cast iron with different wall thicknesses is imaged by high-resolution X-ray CT, and the three-dimensional structure of graphite is observed to clarify the characteristic structural differences and formation process of chunky graphite, etc. As for the volume fractions of graphite structures, when the eutectic solidification time increases, the graphite nodule size becomes coarse. In addition, when the graphite nodule size increases from 60μm to 67μm or more, the shape of the graphite becomes more complex.