Hard Trivalent Chromium Plating from a Concentrated Calcium Chloride Aqueous Solution

A hard chromium plating technique was established using trivalent chromium chloride with a highly concentrated calcium chloride aqueous solution. The obtained films show dense and uniform microstructure, high hardness of 1000 HV and good wear resistance, which are comparable to those of conventional hexavalent chromium plated film. The hardness properties showed little thermal degradation, in contrast to the case of hexavalent chromium film. The carbon content was one magnitude lower than that of a conventional trivalent chromium bath containing carboxylic acids. The lack of thermal degradation of film hardness might derive from the inhibited particle growth resulting from the low carbon content and the high oxygen content. The current efficiency was 60-70%, much higher than those of hexavalent chromium plating and conventional trivalent chromium plating. Because trivalent chromium plating technique using a highly concentrated calcium chloride aqueous solution produces excellent film characteristics and productivity, this plating technique is anticipated as a technology underpinning the industrial production of hard chromium plating.