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고속화염용사코팅으로 제조된 WC-CoFe 코팅의 기계적 특성에 관한 연구
주윤곤 ( Yun Kon Joo ),조동율 ( Tong Yul Cho ),하성식 ( Sung Sik Ha ),이찬규 ( Chan Gyu Lee ),천희곤 ( Hui Gon Chun ),허성강 ( Sung Gang Hur ),윤재홍 ( Jae Hong Yoon ) 한국열처리공학회 2012 熱處理工學會誌 Vol.25 No.1
HVOF thermal spray coating of 80%WC-CoFe powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and hard ceramics coating because of the environmental problem of the very toxic Cr6+ known as carcinogen by chrome plating and the brittleness of ceramics coatings. 80%WC-CoFe powder was coated by HVOF thermal spraying for the study of durability improvement of the high speed spindle such as air bearing spindle. The coating procedure was designed by the Taguchi program, including 4 parameters of hydrogen and oxygen flow rates, powder feed rate and spray distance. The surface properties of the 80%WC-CoFe powder coating were investigated roughness, hardness and porosity. The optimal condition for thermal spray has been ensured by the relationship between the spary parameters and the hardness of the coatings. The optimal coating process obtained by Taguchi program is the process of oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min and spray distance 8 inch. The coating cross-sectional structure was observed scanning electron microscope before chemical etching. Estimation of coating porosity was performed using metallugical image analysis. The Friction and wear behaviors of HVOF WC-CoFe coating prepared by OCP are investigated by reciprocating sliding wear test at 25oC and 450oC. Friction coefficients (FC) of coating decreases as sliding surface temperature increases from 25oC to 450oC. (Received October 31, 2011; Revised November 15, 2011; Accepted December 16, 2011)
SKD61과 Radical Nitriding 처리된 SKD61 기판상에 Arc Ion Plating으로 증착된 TiN 박막의 미세구조 및 기계적 특성, 마찰 및 접착력에 관한 연구
주윤곤(Yun-Kon Joo),윤재홍(Jae-Hong Yoon),방위(Wei Fang),장세굉(Shi-Hong Zhang),조동율(Tong-Yul Cho),하성식(Sung-Sik Ha) 한국표면공학회 2007 한국표면공학회지 Vol.40 No.6
TiN coating on tool steel has been widely used for the improvement of durability of tools. In this work, radical nitriding(RN) is carried out on SKD61 at 450℃ for 5 hours in the ammonia gas pressure 2.7×10³ ㎩. The TiN coating is carried out by arc ion plating(AIP) with the process parameters: arc power 150 A, bias voltage ?50 V, coating time 40 minutes and nitrogen gas pressure 4×10³ ㎩. Hardness, elastic modulus, friction coefficient and adhesion of TiN coating on substrates of both TiN/SKD61 and TiN/RN SKD61 coatings are investigated comparatively. The primary crystalline faces of TiN surface are (200) and (111) for TiN/SKD61 and TiN/RN SKD61 respectively. In addition to the primary phase, Fe phase exists in TiN/SKD61 coating, but not in TIN/RN SKD61. The hardness of TiN/RN SKD61 is about 700 Hv, 250 Hv(56%) higher than that of TiN/SKD61 at the near interface of TiN and substrates. At the TiN surface, hardness of TiN/RN SKD61 is 2,149 Hv, 71 Hv(3%) higher than that of TiN/SKD61. The elastic modulus of TiN coating is improved to 26.7 G㎩(6%) by radical nitriding. The adhesion is improved by the RN coating showing no spalling. buckling and chipping on the scratch test track which are shown on the non-RN TiN/SKD61.