Abstract
Cermet based WC–Co–Cr thermally sprayed coatings are known for their good wear and corrosion performance. Different intermediate layers with various deposition processes were performed between cermet WC–Co–Cr coatings to form a sandwich structure to enhance adhesion and to damp particle impacts during erosion. As the outer cermet layer exhibits high hardness against abrasion whereas the intermediate layer is ductile to damp the shock due to particle impact in erosion, sandwich coatings might have potential improvement in life time of coated tools used in mining, drilling, cutting and grinding. Adhesion tests were performed and the tribological behavior of cermet coating and sandwich structured materials was mainly investigated with dry erosion and high pressure slurry jet erosion tests with 30° and 90° impinging angles to study wear mechanism and particle impact at interfaces between coatings. In this work, the adhesive strength of different coatings was measured for each combination. Cermet coating, combinations of Ni–Cr 80–20 and Ni-plating showed high strength value. In spite of the low erosive wear rate Ni–Cr 80–20, the metallographic examination revealed many cracks within this coating due to the particle erosion at high pressures that has been found to drive microcracks through the interfaces between splats leading to flaking of the sprayed coatings. The electrochemically deposited interlayer showed better tribological performance under metallographic observation, because of its homogeneous microstructure, since the electrochemical deposition does not provide splat formation. Consequently, the absence of discrete interfaces limits crack initiation within the coating and at the interface. However, the microstructure of the interlayer is known to be related to coating deposition process such as microsplats and oxide formation in spraying process. Therefore, the influence of microstructure on wear mechanism was investigated.
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