Warm spray (WS), which is an improved version of high velocity oxy fuel spray (HVOF), can be used to deposit a dense coating of high-strength metals by spraying metal powders with high velocity in the temperature range between that of HVOF and cold spray. In this study, various Ti-6Al-4V coatings formed on an aluminum substrate by WS with different powder sizes and spray conditions were evaluated by laser ultrasonic testing (LUT) so as to study its feasibility as non-destructive testing. The porous internal structure and the rough surface of the Ti-6Al-4V coatings significantly decreased the amplitude of longitudinal and shear waves. As a result, these coating properties had a considerable influence on whether LUT could detect artificially prepared defects in the WS Ti-6Al-4V coatings.

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Mechanical properties of heat-affected cold spray coatings are important. However, the mechanism of multi-scale property change by heat treatment is not well-known. In this study, cold sprayed nickel specimens heat-treated in several conditions were prepared to investigate the influence of heat treatment on the multi-scale properties. Young's modulus and modulus of rigidity were measured by a free resonance method. The microstructure was observed by electron backscatter diffraction (EBSD). The EBSD analysis indicated that the crystal grain size of an as-sprayed coating was finer compared with feedstock powder. The crystal grains grew with increasing heat treatment temperature above 673K. The kernel average misorientation map showed that the strain in the coating disappeared drastically at 673K, and then the hardness decreased. On the other hand, the coating porosity increased with increasing heat treatment temperature above 873K, and then the elastic moduli degreased. It was concluded that microstructure of a nickel coating via cold spray changed with two different scales by heat treatment. First, microscopic strain in the coating was released, and then the macroscopic porosity increased due to diffusion.

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Three types of cold spray (CS) nozzle gas/particle flows were calculated using a one-dimensional computer model. In a conventional CS system, the carrier gas is injected at the converging part of the nozzle (converging-part injection type). However, this paper is focused on the gas/particle flow from the gasdynamic effect of the carrier gas injected at the diverging part of the nozzle (diverging-part injection type). Nitrogen was selected as the process/carrier gases. The stagnation pressure and heater-exit temperature of the process gas were set at 1.5MPa and 600K, respectively. The ratio of the mass flow rate of the carrier gas to that of the process gas was set at 0.1. The calculated results are summarized as follows; 1) The carrier gas injection at the diverging part of the nozzle creates a sudden decrease in the gas velocity, resulting in possible frictional choking. It creates a normal shock wave followed by a subsonic flow in the nozzle. A slower gas flow causes a slower particle velocity. 2) In order to prevent frictional choking, the gas-flow Mach number at which the carrier gas is injected needs to have a larger supersonic value. In addition, the ratio of the nozzle axial length to its inner diameter should decrease. 3) A smaller carrier-gas injection-angle creates a smaller decrease in the gas velocity at the carrier-gas injection point of the nozzle. It lowers the possibility of frictional choking occurring. 4) A diverging-part injection type CS nozzle can provide the equivalent particle velocity and a lower particle temperature compared to the converging-part injection type CS nozzle.

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The pandemic caused by the new type corona virus is now going to change the structure of our society from the ground. Under such a circumstance, we can see so much interest in “ infection ” among us people in the world, inevitably. With the increase interest, the market relating to antibacterial matters is now expanding very rapidly. The antibacterial phenomena can be considered as correlation between materials’ surfaces and microbiome environments. Therefore, problem solving approach from the viewpoint of surface finishing technology can pave the way to establish effective countermeasures. Surface Finishing and Coating technology is one of the promising ways to solve the industrial problems in the field, not only from business, but also from humanitarian standpoints. In this paper, we introduced the evaluation methods for antibacterial, antivirus and antibiofilm coatings in microbiome environments and tried to show our trial research and development for them.

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Photocatalyst coatings have experienced considerable development in the recent years. However, methods for producing high performance photocatalyst coatings are still not fully understood. Thus, in this study, two methods were investigated for generating high performance photocatalyst coatings.
TiO₂ powders with three particle sizes were used to produce the coatings: 7 nm (ST-01), 20 nm (ST-21), and 200 nm (ST-41). The powders were prepared by the spray dry method using a slurry, which was uniformly mixed by bead mill equipment. Agglomerated anatase TiO₂ powders were sprayed by high-velocity oxy-fuel (HVOF) spraying and cold spraying on an A5052 (Al-Mg alloy) substrate. The photocatalyst coating prepared by cold spray exhibited higher photocatalytic performance than that prepared by HVOF. This reduced performance can be attributed to the heat generated from the flame used during spraying. Thus, it is critical to suppress the heating effect on powder particles. Moreover, a phase transformation from anatase to rutile occurred during the HVOF spraying process. Coating by the cold spray method using ST-21 powder shows high photocatalytic performance and high deposition efficiency on the substrate. Moreover, the addition of WO₃ to the TiO₂ slurry improved photocatalytic performance of the sprayed coatings. The decomposition was examined by acetaldehyde gas examination, and the decomposition rate was found to increase by the addition of WO₃ powder. The photocatalyst coating prepared using WO₃ powder (5%) exhibited maximum performance.

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Coronavirus disease 2019 (COVID-19) has spread widely on a global scale. One of the main route of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-29) to cause COVID-19 is a transmission through human respiratory droplets. There seems no relationship between this transmission process of COVID-19 and thermal spray process, but we have notified actually they handled similar phenomena in terms of their physical fluid dynamic behaviors. The formation process of droplet nuclei from a human respiratory system resembles the droplet formation in a suspension thermal spray process. The criteria of the deposition of droplet nuclei of SARS-CoV-2 particles resembles the fine particle behavior in the boundary layer in fine particle thermal spray such as aerosol deposition. The similarity and difference between the SARS-CoV-2 transmission process and the thermal spray process is discussed.

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