Hideki Hamatani, Masahiro Ohara and Masao Fuji
Welding & Joining Laboratory, Nippon Steel Corporation, Futtsu 293
This study is aimed at developing a high power hybrid plasma spraying device with a maximum radio frequency input power of 300 kW, in order to improve the strength and adhesion strength of sprayed coating. The stability of plasma, energy efficiency, and melting state of particles were investigated under several conditions, and then characterization of coating was carried out. The stability of plasma condition is strongly influenced by gas flow rate of Ar, N2, and H2 mixture against the power supplied. The energy efficiency of equipment is approximately 14%. The energy is lost mainly by joule's heat in the oscillator circuit. Using this device, the maximum particle diameter for full melting is approximately 250 μm. In the plasmas praying by not fully melted particles, the strength of coating decreases with increasing particle diameter because of increased porosity size. On the other hand, in the spraying by fully melted particles, it is found that the high strength of coating and the high adhesion strength at the interface between substrate and coating is obtained at large diameter particles. This tendency is explained by easy remelting or sintering at the interface between large particles. Actually, our experiment demonstrates that the maximum strength of coating and adhesion strength is more than 1300 and 250 MPa respectively, by using fully melted particles with maximum diameter.
(Received July 21, 1998; In Final Form September 14, 1998)
plasma spraying, hybrid plasma, radio-frequency plasma, supper alloy, strength of coating, adhesion strength of coating
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