Evaluation of Residual Stresses and Their Influence on Cavitation Erosion Resistance of High Kinetic HVOF and HVAF-Spray
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Evaluation of Residual Stresses and Their Influence on Cavitation Erosion Resistance of High Kinetic HVOF and HVAF-Sprayed WC-CoCr Coatings Tommi Varis1 • Tomi Suhonen2 • Jarmo Laakso1 • Mika Jokipii3 • Petri Vuoristo1
Submitted: 25 November 2019 / in revised form: 6 March 2020 The Author(s) 2020
Abstract Thermal spray processes have been developing toward lower particle temperature and higher velocity. Latest generation high-velocity oxygen-fuel (HVOF) and high-velocity air-fuel (HVAF) can produce very dense coating structures due to the higher kinetic energy typical for these thermal spray processes. Thermally sprayed coatings usually contain residual stresses, which are formed by a superposition of thermal mismatch, quenching and, in case of high kinetic energy technologies, peening stresses. These stresses may have a significant role on the mechanical response and fatigue behavior of the coating. Understanding these effects is mandatory for damage tolerant coating design and wear performance. For instance, wear-resistant WC-CoCr coatings having high compressive stresses show improved cavitation erosion performance. In this study, comparison of residual stresses in coatings sprayed by various thermal spray systems HVOF (Thermico CJS and Oerlikon Metco DJ Hybrid) and HVAF (Kermetico AcuKote) was made. Residual stresses were determined through thickness by utilizing Tsui and Clyne
This article is part of a special topical focus in the Journal of Thermal Spray Technology on Advanced Residual Stress Analysis in Thermal Spray and Cold Spray Processes. This issue was organized by Dr. Vladimir Luzin, Australian Centre for Neutron Scatte & Tommi Varis tommi.varis@tuni.fi 1
Materials Science and Environmental Engineering, Tampere University Ringgold Standard Institution, Korkeakoulunkatu 6, P.O. Box 589, Tampere 33014, Finland
2
Material Modeling and Ecodesign, VTT Technical Research Centre of Finland, Espoo, Finland
3
Nuclear Reactor Materials, VTT Technical Research Centre of Finland, Espoo, Finland
analytical model. The real temperature and deposition stress data were collected in the coating process by in situ technique. That data were used for the model to represent realistic residual stress state of the coating. The cavitation erosion and abrasion wear resistance of the coatings were tested, and relationships between residual stresses and wear resistance were discussed. Keywords cavitation-resistant coatings fracture toughness HVAF HVOF in situ monitoring residual stresses WC-CoCr
Introduction The unique droplet-by-droplet manufacturing process of thermally sprayed coatings may generate relatively high residual stresses, which are necessary to understood and controlled well to avoid residual stresses causing failures during the coating manufacturing process or in use (Ref 13). Some of the latest high kinetic thermal spray processes, such as high-pressure high-velocity oxygen-fuel (HVOF) or high-velocity air-fuel (HVAF), typically produce lower flame temperatures and higher par
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