The effects of pH and heat treatment on morphology, structure and hardness of Co-P Coatings electrodeposited by DC current

Co-P electrodeposites are appropriate substitute for hard chromium coatings due to their suitable properties. In this study, nano-crystalline and amorphous Co-P coatings were deposited on plain carbon steel substrates using a direct current and their morphology was examined. The effect of pH on morphology, current efficiency, phosphorus content, hardness and preferred orientation of the coatings were investigated. Moreover, the effect of heat treatment on microstructure and hardness of the nano-crystalline and the amorphous coatings was studied. The results showed that, phosphorus content and hardness of the coatings were decreased by increasing the pH from 1 to 4 in spite of an enhancement in the current efficiency up to 98%. Preferred orientation and morphology of the coatings were also changed by increasing of pH values. Hardness numbers of the amorphous and the nano-crystalline coatings, deposited at the optimum condition, were about 750 and 600 HV, respectively. These values were increased and reached 1090 and 760 HV by heat treatment.