Characterization of intermediate Cr-C layer fabricated by electrodeposition in hexavalent and trivalent chromium baths

The effect of formic acid and current density on the crystal structure, surface morphology and crystallization of intermediate Cr-C layers deposited in both hexavalent and trivalent chromium baths were studied to observe chrome-carbide formation behavior and to develop an environmental protective Cr-C electroplating technology. Formic acid in hexavalent and trivalent chromium baths effectively produces intermediate Cr-C layers. The intermediate Cr-C layers has initially amorphous type microstructure. Crystallization of the intermediate Cr-C layer occurs at a current density above 27.5 A/dm2 in a trivalent chromium bath and above 100 A/dm2 in an hexavalent chromium bath, respectively. The carbon content of the intermediate Cr-C layer prepared in hexavalent chromium bath is twice as much as that of the layer prepared in trivalent chromium bath. Cr23C6 and Cr7C3 were observed in the intermediate Cr-C layer prepared in hexavalent chromium bath, whereas, Cr23C6 was formed in the layer prepared in trivalent chromium bath after vacuum annealing at 800 °C.