Materials Performance

SEP 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 88 of 128

30 SEPTEMBER 2018 W W W.MATERIALSPERFORMANCE.COM COATINGS & LININGS T A cermet is a metallic matrix with dis- persed ceramic particles. Tungsten carbide dispersed in nickel (WC-Ni) is a cermet. This article discusses WC- Ni brazing on the surface of an impel- ler to improve wear and corrosion re- sistance. The coating was applied in a conventional vacuum furnace while rotating the impeller to develop a homogeneous and uniform coating layer during the brazing process. Ap- propriate revolutions per minute were derived using the finite element method with input on centrifugal and gravity forces. The service life of the impeller with the WC-Ni brazed coat- ing was measured to be almost eight times longer than the life of the non- brazed impeller. The application of surface treatments— coating layers with properties superior to those of the substrate—generally are used to improve the service life of equipment in i n d u st r i a l s e tt i n g s . 1 - 2 C o n t r o l l i n g t h e surface layer's mechanical properties is considered to be an important attribute for current engineering applications. Minor damage of the surface sometimes results in mechanical component failure, which has caused fatal accidents. Surface treatments can also provide a longer service life with a consequent reduction of total costs. 3 WC-based composite layer coatings have good resistance to abrasive and ero- sive wear due to the presence of WC parti- cles that are dispersed in an alloy binder such as nickel or cobalt. 4 Thermal spraying, such as high-velocity oxygen f lame spray- ing, plasma spraying, wire arc spraying, flame spraying, and other techniques, 5 is a useful technology to produce WC-based composite layer coatings. Because it is a mechanically bonded coating, however, thermal spraying has low bond strength between the coating layer and the sub- strate. Also, it exposes the WC powder to oxygen or water vapor, w hich leads to porosity and oxide formation. 3 Another process for preparing a WC composite layer coating is based on the infil- tration brazing technology. In brazing, the substrate is wetted by the melted filler metal and a metallurgical bond is formed. The bond strength is superior to that of thermal sprayed coatings. 6 It can be applied to curved, inner, or outer surfaces simultane- ously, which can reduce the cost of machin- ing the coating surface after brazing. It also has less distortion, lower residual stresses, and lower substrate dissolution. 7 Tungsten carbide dispersed in nickel (WC-Ni) is a cermet, which is a metallic matrix with dispersed ceramic particles, and is widely used in industries due to its high hardness and good wear resistance. Gao, et al. 8 reported on a WC-Ni brazed coating made with WC and Ni-based metal powders applied through high-temperature vacuum brazing. Lu and Kwon 6 reported that wear resistance of the WC-Ni brazed coating is better than other overlaid coat- ings under wet sand abrasive wear and rotating slurry erosive wear. Klaasen, et al. 9 investigated th e strength and residual stress between a WC-Ni brazed coating and the substrate. They found that the plastic- ity and proof stress of the filler metal affect the reliability of WC-Ni brazed coating. Development of WC-Ni Cermet Brazing Process Hyung g oun Joo, School of Mechanical Engineering, Yonsei University, Seoul, South Korea Kang y ong Lee, State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Liaoning, People's Republic of China g uo Ming Luo and d a Quan Z H ang, Department of Environmental Engineering, Shanghai University of Electric Power, Shanghai, People's Republic of China

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