Digital Repository, Youth Symposium on Experimental Solid Mechanics

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Nanocrystalline cobalt-phosphorous alloy plating for replacement of hard chromium
Katarzyna Rymer, Andrzej Przywóski

Last modified: 2010-09-06




Nanocrystalline cobalt-phosphorous (nCo-P) coatings electrodeposited by pulse plating are presented as a viable alternative to electrolytic hard chromium plating. An electrolytic process is evaluated for electrodepositing a cobalt alloy which contains at least about 2 to 25% atomic volume of phosphorous. Electroplating of Co-P from citrate baths has been investigated under different conditions of current density and pulse sequences. The influence of these variables on the morphology, structure, hardness, internal stress and corrosion properties of deposited coatings has been studied in details. Wide range of current densities can be applied in this electroplating process, but not greater than about 3,5 A/dm2 to permit low stress plating. In general it is indicated that the hardness of Co-P deposits containing phosphorus concentrations between 3 to 25 wt%, can be increased to values exceeding 900VHN by annealing at a temperature greater than 300°C for a suitable period of time. Nanocrystalline cobalt-phosphorus (30 μm thick) exposed to the environment in a salt spray chamber operated according to the requirements of ASTM B117-97, performed very well, decreasing to only a 9/8 Protection/Appearance rating after 400 h exposure time.