터보불로워 용 회전체 주축 소재의 마찰, 마모 및 부식 저항 향상을 위한 WC-metal 분말의 초고속화염용사코팅

Abstract

High velocity oxy-fuel (HVOF) spray coating of WC-metal powder (powder) was carried out to improve the resistances of friction, wear and corrosion of magnetic bearing shaft material Inconel718 (In718) of turbo blower. A micron sized WC-metal powder (86.5% WC, 9.5% Co 4% Cr) was coated onto In718surface using HVOF thermal spraying. During the spraying, the binder metals and alloy such as Co, Cr and Co-Cr alloy were molten and a small portion of WC particles were partially decomposed to W2C and free carbon at above its decomposition temperature of 1250ºC. The free carbon and excessively sprayed oxygen formed carbon oxide gases, resulting a porous coating of porosity of 2.2±0.3%. The surface hardness of substrate increased approximately three times from 400 Hv of In718 to 1260±30 Hv of the coating The friction coefficients of the coating were approximately 0.33 ± 0.03 at 25ºC and 0.26 ± 0.03 at 450ºC. These values were smaller than those of In718 substrate at both temperatures due to the lubrication from the free carbon and the cobalt oxide debris. The corrosion resistance of the coating was higher than that of In718 both in salt water of 3.5% NaCl and acid of 1 M HCl solutions, on the contrary, it was lower in base solution of 1 M NaOH. According to this study, the HVOF WC-metal powder coating is recommended for the durability improvement of magnetic bearing shaft of turbo blower.