Trends of thermal spraying technology in Japanese steel industry is summarized by investigating the patent applications filed in Japan Patent Office in the past 20 years from FY1990 to FY2009. The total number of patents filed in 8 Patent Offices (Japan, United States, Europe, China, Korea, Russia, Brazil and India), retrieved by the International Patent Classification symbol C23C4/00 (IPC index key: Coating by spraying the coating material in the molten state ), is 15,082. The ratio of patent applications filed in each Patent Office is as follows: JP (39%), US (22%), EP (17%), CN (9%), KR (6%), RU (3%), BR (3%) and IN (1%). The database used in this study is from commercially available “PatBase”. Number of patent applications of thermal spray technology (C23C4/00) in Japan is 4,369. Among these patents, the ratio of patents related to steel industry filed by major Japanese steel companies is 13% of total patents of every industrial segment in Japan. These patents are classified according to (1) coating applications in the process of steel production lines, (2) performances and effects obtained by coatings, .and (3) coating materials. In this paper, current status and future trend of thermal spray technology in Japanese steel industry is discussed.

Thermal sprayed ceramic coatings are well used as the electrode of corona discharge treatment in order to modify the surface of many kinds of films and papers due to its superior durability and adaptability. Some kinds of Al 2 O 3 -TiO 2 were sprayed by APS on the parallel plate electrodes, and output power of corona discharge generated by the electrodes was measured by using Sawyer-Tower circuit. In addition, discharge output power was calculated with an equivalent circuit of corona discharge. By comparing them, effects of the electrical property of the coating on discharge was researched. As a result, the electrostatic capacitance of the coatings influences the impedance of the whole circuit, and higher relative permittivity of the coating brought higher output power in a constant voltage.

Damage of marine screw propeller parts made of aluminum bronze cast material caused by cavitation erosion is one of the serious problems. Erosion resistant thermal spray coating on aluminum-bronze material is expected to extend lifetime of such propellers. In this study, Cobalt-based alloy coatings sprayed by; (a) atmospheric plasma spraying (APS), (b) low pressure plasma spraying (LPPS) and (c) high velocity oxy-fuel (HVOF) spraying and aluminum bronze cast material were evaluated by cavitation erosion test using magnetostrictive cavitation test equipment. Fracture morphology of cavitation eroded coating surfaces were analyzed by surface observations with SEM and also the amount of volume loss was measured. Cobalt-based alloy coatings sprayed by LPPS exhibited superior cavitation erosion resistance compared to aluminum bronze cast material and coatings by APS and HVOF. Moreover, mechanical properties of Cobalt-based alloy coatings were investigated in detail by nanoindentation technique. It is found that cavitation erosion resistance of coatings is subjected to interparticle cohesive strength.

Thermal spray technology trends in Japan were studied on the basis of patent information related to such technologies in Japan. Information related to research in and the basic development of thermal spray and allied coating technologies can be found in publication papers or documents submitted to national or international conferences, symposiums academic journals and so on. However, this kind of information does not always disclose key fundamentals pertinent to the industry in question. The present status of thermal spray technology and related future trends in Japan are described in this paper based on an investigating of patent filings, claims, and the specific industrial fields and applications related to such patent applicants.