Journal
SURFACE & COATINGS TECHNOLOGY
Volume 207, Issue -, Pages 443-449Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2012.07.047
Keywords
Pulse plating; Electrodeposition; Nanocrystalline coatings; Cobalt-phosphorous; X-ray diffraction; Transmission electron microscopy
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Co-P alloy coatings were electrodeposited from a Watts type base electrolyte using a galvanostatic pulse plating technique. Alloy deposits of P content as low as 1% were obtained operating at very high pulse current density and low duty cycle from an electrolyte with a small concentration of phosphorous acid, in the presence of a surfactant and a stress reliever. Alloy deposits with low P content - in the range 1-2% - had a peculiar mixed nanociystalline-amorphous structure: a fully amorphous deposit was obtained when the P content was in excess of about 5-6%. A short and relatively low temperature annealing of the mixed structure triggered a strong enhancement of the hardness, in connection with the precipitation of a phosphide phase in a slightly regenerated nanocrystalline structure. The remarkable thermal stability of the transformed structure of the alloy was lost in conjunction with the on-set of the allotropic transformation from hcp to fcc-Co. A side effect of the hardening was the cracking of the layer and its obvious impact on the protective performance of the Co-P alloy deposit. Alloy deposits with low P content and a mixed nanocrystalline-amorphous structure hold promise as alternative to traditional electroplated hard coatings. (c) 2012 Elsevier B.V. All rights reserved.
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