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Influence of post-treatment on the microstructural and tribomechanical properties of suspension thermally sprayed WC-12 wt%Co nanocomposite coatings
: Ali, O.; Ahmed, R.; Faisal, N.H.; Alazani, N.M.; Berger, Lutz-Michael; Kaiser, Arno; Toma, Filofteia-Laura; Polychroniadis, E.K.; Sall, M.; Elakwah, Y.O.; Goosen, M.F.A.
The potential to improve the tribomechanical performance of HVOF-sprayed WC-12Co coatings was studied by using aqueous WC-12Co suspensions as feedstock. Both as-sprayed and hot-isostatic pressed (HIPed) coatings were studied. Mathematical models of wear rate based on the structure property relationships, even for the conventionally sprayed WC-Co hardmetal coatings, are at best based on the semi-empirical approach. This paper aims to develop these semi-empirical mathematical models for suspension sprayed nanocomposite coatings in as-sprayed and heat-treated (Host Isostatically Pressed (HIPed)) conditions. Microstructural evaluations included Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The nano hardness and modulus of the coated specimens was investigated using a diamond Berkovich nano indenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that the HIPing post-treatment resulted in crystallization of amorphous coating phases and increase in elastic modulus and hardness. Influence of these changes on the wear mechanisms and wear rate are discussed. Results are also compared with conventionally sprayed High Velocity Oxy-Fuel (HVOF) hard metal WC-Co coatings.