Element concentration mapping

Fig. 1 Process of absorption edge formation (top). 3D concentration mapping of copper in Al-5Cu as-cast alloy and solution-treated specimen (bottom left). At a glance, copper seemed to be evenly distributed after heat treatment, but there were large local differences, as shown in the bottom-right figure.

@Monochromatic X-ray CT is effective for determining the 3D distribution of element concentration in binary system alloys (Review paper 1),but not in materials consisting of three or more components. A high-contrast imaging method that involves taking transmission images of both sides of an absorption edge, calculating the difference, and selectively emphasizing a specific element, has been used in the field of medicine. By calculating the picture element differences, through precisely adjusting the locations of the images and correcting picture element values, it is possible to perform 3D/4D element concentration mapping (Review paper 2). Theoretically, the method can be applied to elements that have an absorption edge in the energy range that produces monochromatic light with SPring-8, i.e., from Fe (atomic number: 26) to Bi (atomic number: 83). It ensures similar detectability and reproducibility to those of SEM-EDX (Paper 1),and has been used to assess the spatial non-uniformity of microstructures and its effects on fracture(Paper 2, 3Review paper 3).

Fig. 2 Visualization of Zn concentration distribution in foamed Al-10Zn-1.5Ca-1.5Ti-1.0Mg by absorption edge difference imaging. The 4D observation of the fracture process clearly demonstrated the relationship between the fracture pathway and the regions of high Zn concentrations.

@The Cu concentration distribution in Al-Cu alloy is shown in Fig. 1 as an example (Paper 1). Sufficiently long homogenization at a high temperature seemed to have uniformized the Cu concentration. However, the mean Cu concentration and the distribution of Cu distribution differed markedly among 10 spherical regions that were sampled and assessed. Figure 2 shows the relationship between the zinc segregation in a porous material, and the pathway of crack propagation during fracture (Paper 2).It clearly demonstrates that local fluctuations of alloy element concentration similar to those shown in Fig. 1 determined the fracture. Concerning the positive and negative effects of solution treatment at an extremely high temperature, which caused melting of the eutectic compounds, this method was also effective in visualizing the preferential fracture in zones that were brittle with respect to the melting of the eutectic compounds(Paper 3).

Review paper

  1. H. Toda, M. Kobayashi, Y. Suzuki, A. Takeuchi, K. Uesugi, X-ray Micro- and Nano-tomography Techniques and Their Applications, Kenbikyo, Vol.44CNo.3C2009C199-205.
  2. H. Toda, M. Kobayashi, Y. Suzuki, A. Takeuchi, K. Uesugi, 3D¥4D Materials Science: Its Current State and Prospects, Hihakaikensa, Vol.58CNo.10C2009C433-438
  3. H.Toda, M. Kobayashi, Fracture Behavior Analysis in Pours Metals by X-ray Micro-tomography, Materia, Vol.47CNo.4C2008C191-195.
  4. H. Toda, M. Sato, H. Okuda, M. Kobayashi, Observation and analysis of materials with synchrotron radiation, Keikinzoku Vol.61, No.1, 2011

Research paper

  1. H. Toda, K. Shimizu, K. Uesugi, Y. Suzuki and M. Kobayashi, Application of dual-energy K-edge subtraction imaging to assessment of heat treatments in Al-Cu Alloys, Materials Transactions, Vol. 51, No.11, 2010, 2045-2048
  2. Q. Zhang, H. Toda, Y. Takami, Y. Suzuki, K. Uesugi, M. Kobayashi, Assessment of 3D inhomogeneous microstructure of highly alloyed aluminium foam via dual energy K-edge subtraction imaging, Philosophical Magazine, Vol.90, No.14, 2010, 1853-1871
  3. H. Toda, T. Nishimura, K. Uesugi, Y. Suzuki, M. Kobayash, Influence of high-temperature solution treatments on mechanical properties of an Al-Si-Cu aluminum alloy, Acta Materialia, Vol.58, 2010, 2014-2025