Nanocrystalline hard chromium electrodeposition from trivalent chromium bath containing carbamide and formic acid: Structure, composition, electrochemical corrosion behavior, hardness and wear characteristics of deposits

The paper is devoted to the structure, composition and properties investigations of coatings obtained from a sulfate trivalent chromium bath containing formic acid and carbamide as the complexing agents. The results indicate that the deposits have a nanocrystalline type of structure-there are regions with atomic ordered arrangement in bulk material with the average size of 3-5 nm. Carbon is present as chromium carbide within the coating and it is distributed uniformly inside of the deposit. The deposits under study exhibit particular electrochemical behavior (absence of the active dissolution range in acid solution). The hardness of these coatings does not differ noticeably from that typical of coatings obtained in Cr(VI)-based baths. The wear characteristics of the deposits from the proposed bath are somewhat better than in the case of a common hexavalent chromium bath.