Thermal barrier coatings (TBCs) are essential for the turbine blades of high-efficiency gas turbine combined cycles. A typical TBC system consists of a metal bond coat (BC) with high-temperature corrosion resistance on a superalloy substrate and a ceramic top coat (TC) using the air plasma spraying (APS) process. Recently, the suspension plasma spraying (SPS) process enabled finer microstructural control than the APS one by using fine spray particles of sub-micron size with a solvent as a suspension. It has been reported that the TBC with a columnar structure sprayed by using the SPS method has superior thermal fatigue resistance. However, there is little information about internal stress distribution in the SPS-TBC. In this study, the internal stress distribution of the SPS-TBC with a columnar structure subjected to tensile loading was evaluated by the high-energy synchrotron X-ray and the low-energy X-ray diffraction analysis. Experimental results revealed that the internal stress in the SPS-TBC was lower than the conventional APS-TBC due to the stress relaxation mechanism of the SPS-TBC' s columnar structure. The SPS-TBC exhibited a periodic residual stress reduction in the out-of-plane direction. The finite elemental analysis was also conducted using the column structure models. Based on the comparison between the experimental and analysis results, the effect of microstructure on the internal stress distribution of the SPS-TBC was discussed.

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3D printers, also known as additive manufacturing (AM) , have been developed for industrial production processes. In particular, the progress in metal AM technologies is opening innovative opportunities in the production of highly durable parts. Powder bed fusion (PBF) is one of the most feasible processes for metal AM. The combination of in-situ observation experiments, post-fabrication microstructural observation, and computer simulations has revealed that crystal growth occurs under extreme conditions that differ significantly from those in conventional solidification processes. In PBF, the melting and solidification of metal by laser or electron beam scanning is accompanied by a cooling rate of over 10⁶ K/s, a temperature gradient of over 10⁷ K/m, and a growth rate of up to 1 m/s. This review paper introduces the unique microstructures that have been found in metals fabricated by PBF and the methods to obtain scientifically useful knowledge from the analysis of physical model simulation, which we call " digital twin science ". The mechanisms of crystal growth and microstructure formation in PBF-type metal AM are reviewed.

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The historical situation and development of thermal spray technology and industry in Japan are summarized. The content covers four items to highlight the activities of thermal spray in Japan as hereinafter described. At first, the origin of thermal spray technology and its development are introduced. Secondary actual applications in the industry field are characterized by employing the coating performances, at the same time the examples of process technologies that are employed for the manufacturing thermal spray coating products are described. The market size of thermal spray industry in Japan is also estimated by references employing a few statistics. Finally, some technical issues are proposed.

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