Sliding wear evaluation of hot isostatically pressed thermal spray ceramet coatings
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V. Stoica, R. Ahmed, M. Golshan, and S. Tobe (Submitted 21 August 2002; in revised form 10 December 2002)
The principal aim of this study was to compare the sliding wear performance of as-sprayed and Hot Isostatically Pressed (HIPed) thermal spray cermet (WC-12Co) coatings. Results indicate that HIPing technique can be successfully applied to post-treat thermal spray cermet coatings for improved sliding wear performance, not only in terms of coating wear, but also in terms of the total volume loss for test couples. WC-12Co coatings sprayed by a HVOF system were deposited on SUJ-2 bearing steel substrate and then encapsulated and HIPed at 850 °C for one hour. A high frequency reciprocating ball on plate rig was used to measure the sliding wear resistance of these coatings in dry conditions under steel and ceramic contact configurations at two different loads. Results are discussed in terms of coating microstructure, microhardness, fracture toughness and residual stress evaluations. Microstructural investigations indicate fundamental changes in grain morphology, whereas x-ray diffraction revealed beneficial transformations in phase composition of these coatings during the HIPing post treatment. The effects of these microstructural changes on the physical properties and wear resistance are discussed.
Keywords
hot isostatic pressing, mechanical properties, microstructure, residual stress, sliding wear, thermal spray coatings, WC-Co, wear mechanisms
1. Introduction Thermal spray coatings technology has evolved to be one of the preferred techniques for applying coatings of various metallic, ceramic, and polymer materials on a variety of substrates. The design of such surface engineered components thus caters to the economical, technological and environmental challenges faced by the industry. In wear-resistant applications, the coated layer provides the resistance to wear, while the substrate supports the impact to which the system (coating and substrate) is subjected. Various thermal spraying techniques can be used to achieve the best combination of coating and substrate properties for industrial applications. Nowadays, advances in thermal spraying make possible the replacement of bulk components in paper milling[1] or the replacement of chromium plating in aircraft manufacturing[2,3] or automotive industry.[4,5] Also the deposition of thermally sprayed coatings on critical parts in petroleum drilling[6] or on components in aero-applications such as fans and high-pressure compressors[7,8] were successful using detonation gun spraying (D-Gun), high velocity oxygen fuel (HVOF), and atmospheric plasma spraying (APS). To bear the severe wear conditions in service life, a component should have, beside the high hardness, an acceptable level V. Stoica and R. Ahmed, Heriot Watt University, School of Engineering and Physical Sciences, Riccarton, Edinburgh, EH14 4AS, United Kingdom; M. Golshan, CLRC, Daresbury Laboratory, Warrington, Cheshire, WA4 4AD, United Kingdom; S. Tobe, Ashikaga Institute of Technology, 268 Ohmaecho, Ash
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