Tribological Properties of Hard Metal Coatings Sprayed by High-Velocity Air Fuel Process
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C. Lyphout, K. Sato, S. Houdkova, E. Smazalova, L. Lusvarghi, G. Bolelli, and P. Sassatelli (Submitted April 2, 2015; in revised form July 16, 2015) Lowering the thermal energy and increasing the kinetic energy of hard metal particles sprayed by the newly developed HVAF systems can significantly reduce their decarburization, and increases the sliding wear and corrosion resistance of the resulting coatings, making the HVAF technique attractive, both economically and environmentally, over its HVOF predecessors. Two agglomerated and sintered feedstock powder chemistries, WC-Co (88/12) and WC-CoCr (86/10/4), respectively, with increasing primary carbides grain size from 0.2 to 4.0 microns, have been deposited by the latest HVAF-M3 process onto carbon steel substrates. Their dry sliding wear behaviors and friction coefficients were evaluated at room temperature via Ball-on-disk (ASTM G99-90) wear tests against Al2O3 counterparts, and via Pin-on-disk (ASTM G77-05) wear tests against modified martensitic steel counterparts in both dry and lubricated conditions. Sliding wear mechanisms, with the formation of wavy surface morphology and brittle cracking, are discussed regarding the distribution and size of primary carbides. Corrosion behaviors were evaluated via standard Neutral Salt Spray, Acetic Acid Salt Spray, accelerated corrosion test, and electrochemical polarization test at room temperature. The optimization of the tribological properties of the coatings is discussed, focusing on the suitable selection of primary carbide size for different working load applications.
Keywords
carbides grain size, corrosion, hard metal, HVAF, HVOF, sliding wear, tribology
1. Introduction In the field of protective coatings against wear and corrosion, recent restrictions in the use of the carcinogenic hexavalent form of chromium have driven the need of replacing Electrolytic Hard Chrome plating (EHC) by other materials/processes with equivalent tribological properties (Ref 1). Alternatives to EHC have emerged in the past decades in the field of thermal spray technology, which also allowed an improvement of the surface properties of critical components (Ref 2, 3), such as hydraulic pistons, ball valves, turbine valves, rolls and plungers, found in oil production systems, hydroelectric power plants, paper and mining industries, and desalinization This article is an invited paper selected from presentations at the 2015 International Thermal Spray Conference, held May 11-14, 2015, in Long Beach, California, USA, and has been expanded from the original presentation. C. Lyphout, University West, Trollha¨ttan, Sweden; K. Sato, Fujimi Incorporated, Kakamigahara, Japan; S. Houdkova and E. Smazalova, University of West Bohemia, Plzenˇ, Czech Republic; and L. Lusvarghi, G. Bolelli, and P. Sassatelli, University of Modena and Reggio Emilia, Modena, Italy. Contact e-mails: [email protected], atouk@fujimiinc. co.jp, [email protected], and [email protected].
Journal of Thermal Spray Technology
plants. In this field of application,
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