Electrodeposited chromium coating, Trivalent chemical baths, Cr-C alloy, Cr-C-P coating, Annealing
Chromium coating in elevated-temperature environments
The invention introduces a strategy to improve upon Cr-C plating derived from a trivalent bath through the addition of Phosphorous to the coating. Phosphorous is incorporated into the coating when hypophosphite-based baths are employed, but may also be introduced by addition of hypophosphite in organic baths, or by electroless deposition. The improved coating has hardness greater than 900 kgf/mm2 in advantageous conditions, and may similarly have hardness greater than 1000 kgf/mm2 at a temperature greater than 6500C. The coating can be deposited electrolytically or in the form of vapor. The coating should be exposed to a sufficient temperature to produce body centered cubic chromium, and annealed for at least five minutes. Upon thermal treatments, chromium nanocrystallization as well as precipitation of carbides and phosphides occurs, and the mechanical properties of the coating are improved. Detail composition of electrolytic baths can also be provided.
US Patent Number 7,910,231, issued on March 22, 2011
Last revised: April 29, 2013
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