Electrodeposition of amorphous chromium deposits

摘要

Because of their micro-cracked structure, chromium coastings exhibit comparatively poor corrosion resistance in spite of their otherwise excellent physical properties. Drawing on the analogy of the superiority of nickel-phosphorus coating to those of nickel, improved corrosion resistance was predicted with the incorporation of metalloids in the deposit. Thus amorphous chromium-carbon deposita with a smooth surface morphology and chromium-phosphorus deposits from a Cr(III) bath were formed, with atendency to cracking and high hardness values. Where these deposits are crack4ree, they show good corrosion resistance. Phosphorus-containing amorphous deposits were also formed from hexavalent chromium baths in which the proportion of metalloids depended on current density and additive concentration. after heat-treatment, these exhibited hardness values up to 1500 HV with good corrosion resistance where they were crack-free.