Microstructure and properties of carbon-sulfur-containing chromium deposits electroplated in trivalent chromium baths with thiosalicylic acid

摘要

The chromium-carbon-sulfur (Cr-C-S) deposits were electroplated from a trivalent Cr bath containing thiosalicylic acid. In the absence of thiosalicylic acid, the Cr-C deposit was amorphous and contained a significant amount of C. The Cr-C-S deposit plated in the bath containing thiosalicylic acid displayed a crystalline structure and was mainly composed of Cr, C, S, and oxygen. The presence of thiosalicylic acid in the bath apparently reduced the codeposition of C, which, in turn, enhanced the crystallinity of the Cr-C-S deposit. Furthermore, the codeposited S influenced the microstructure and properties of the deposits. The internal stress and population density of cracks of the deposit were reduced as more thiosalicylic acid was added in the trivalent Cr bath. Moreover, the corrosion potential was enhanced and the corrosion current density and the passivation current density were reduced with increasing bath thiosalicylic acid concentration. As a result, the crystalline, crack-free Cr-C-S deposit exhibited a better corrosion resistance than the amorphous Cr-C deposit.