The Electrodeposition and Properties of Amorphous Chromium Films Prepared from Chromic Acid Solutions

The addition of organic compounds containing a or group such as formamide, formaldehyde, glyoxal or formic acid to a chromium electroplating bath results in a chromium deposit which has greatly improved properties compared to conventional chromium deposits. These layers have fewer defects, and the as‐deposited, amorphous layers have a Vicker's hardness of about 1000, which is comparable to that of conventional chromium plating deposits. With annealing in air, the hardness goes through a maximum of about 1700 at 500°–600°C, while the hardness of a conventional plating decreases monotonically from 1000 to 400, with annealing from 200° to 800°C. X‐ray diffraction and differential thermal analysis show that annealing up to about 600°C causes formation and growth of chromium crystallites and that chromium carbides form above this temperature. These layers are also more resistive to corrosion by hydrochloric acid than conventional chromium layers.