Study of Ni 63 -Co 37 nanocrystalline electrodeposited alloy as anti-wear coating on mild steel substrate
Résumé
Ni63-Co37 nanocrystalline electrodeposited alloy is studied as wear protective coating on StW24 mild steel. The analyses of coatings composition by XRF demonstrate an anomalous codeposition behavior of Ni-Co alloy. SEM shows that saccharine leads to the nanometric granular grains of Ni-Co coatings. XRD pattern of Ni-Co deposits confirms that the addition of saccharin in the electrolyte leads to crystallites size in the nanometric order and also to the predominance of (111) as preferential crystallographic orientation. Vickers micro-indentation shows that the solid solution hardening and the Hall-Petch strengthening lead to hardness of Ni-Co coating three times higher than that of substrate. The pin-disc wear tests under dry sliding conditions reveal that Ni-Co coated steel has much higher wear resistance than the uncoated substrate thanks to its relatively higher hardness, but the coated substrate shows higher friction coefficient because the formation of uncompleted tribofilm on its worn surface due to its specific wear mechanism, where SEM observations on the wear tracks morphologies of the uncoated and Ni-Co coated substrate show that the mechanism governing the wear of the bare steel is an abrasive oxidative mechanism, whereas that of the Ni-Co coated substrate is a mixed adhesive-abrasive oxidative mechanism.