Influence of post-heat treatment and complexing agents on hardness of Ni-Cr alloy coatings

摘要

The presence of complexing agents in theelectroplating bath and post-heat treatment are two factors whichinfluence the structure of electroplated alloy coatings. Any changein structure is accompanied by changes in coating physical andmechanical properties such as hardness. The aim of this study wasto investigate the effects of complexing agents present in theelectroplating bath and post-heat treatment on the hardness ofelectroplated Ni-Cr coatings obtained from two different baths,one containing sodium citrate as its complexing agent and theother containing dimethyl-formamide. The hardness of coatingsobtained from both types of electroplating bath increased withcoating chromium content. Coatings obtained from the sodiumcitrate bath were generally harder than those obtained from thebath containing dimethyl-formamide. Alloy coatings with 18 and35%Cr were selected for this study. The hardness did not decreaseafter heat treatment up to about 300 deg C, but further increase inannealing temperature caused a sharp decrease in the hardness ofdeposits. This decrease in coating hardness with increase in theannealing post-heat treatment temperature was observed for all coatings.