| Co-Investigator(Kenkyū-buntansha) |
OHSHIMA Ikuya Ibaraki Univ., Mech. Eng., Assistant, 工学部, 助手 (80007632)
MURATA Ryoji Sci. Univ. Tokyo, Mech. Eng., Professor, 理工学部, 教授 (70201811)
前川 克廣 茨城大学, 工学部, 助教授 (20126329)
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| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 1990: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1989: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
Ceramice are used not only as structural components but also as thin films coated over metals and allovs. The latter use, such as thermal barriers for gas turbine and unti-wear coatings for guideways and moving parts, has been becoming more popular owing to developing coating technologies. In terms of splayung ceramics, industrial applications are limited to some extent since the bond strength of coatings is less than one tenth of the bulk mental. In order to increase the strengh, pretreatments such as cleaning and roughening of the surface to be sprayed play an imporatant role. Scratching or grit blasting is usual, and precheating above 150 ^ﾟC is a necessary process as well.
The purpose of the present study is to develop a new technology to raise the bond strength between ceramic coatings and bulk metals. A surface just after being cut is chemically active because of its high clemanness and a moderate temperature above 100 ^ﾟC. Keeping these characteristics of metal cutting in mind, w
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e have proposed a clean-cut spraying in which ceramic particles melted by a plasma heat source are sprayed on the machined surface immediately after the cut.
Choosing a structural steel for the bulk metal and an alumina for the spray powder, we investigated spraying conditions, such as cutting conditions and the distance between a spray gun and the substrate. Low cutting speeds and low feed rates in conjunction with an existing built-up edge were found to yield higher bond strength. The optimum distance was 40 mm for spraying on the outer surface of the bar substate, and 60 mm for the section spraying.
The maximum values of thickness, hardness and bond strength of the alumina ceramic coating were 0.31mm/pass, 76 (SUPERFICIAL 30-N) and 38 Kgf/cm_2, respectively. Thermal cycling and thermal shock tests of the coating showed that the clean-cut spraying was superior to the conventional spraying where grit blasting was used.
In conclusion, though effectiveness of the proposed method is derived from making full use of the activated surface by machining, machining plays a sudsidiary role to raise the bond strength since a chip removes heat excessively supplied on the substrate during plasma spraying. Further studies are needed to clarify the bond mechanism in the clean-cut spraying, to examine effects of bond coating and another characteristics of clean-cut sprayed coatings, to combine post-processing such as grinding with the present system, and so forth. Less
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