Gradual Change of Pulse Parameters as a New Strategy for Synthesis of Functionally Graded Ni-Cr Coatings

Abstract

Synthesis of functionally gradient coating was the main goal of researches to cover some deficiencies of metallic coatings. In this study, a new strategy for generating functionally gradient coatings of nickel-chromium on a carbon steel substrate using pulse electrodeposition has been presented. The gradual changes of the duty cycle and pulse frequency were used to generate the functionally gradient coating, and the chemical composition, microstructure, microhardness, wear and corrosion of them were investigated. Gradual changes of the duty cycle from 45 to 80% led to a gradient structure with a chromium content of 83% on the surface and 3% in the vicinity of the interface. Frequency changes had no significant effect on the chemical composition and did not result in the production of gradient coatings. In both groups, wear resistance improved related to the monolayer one so that weight loss in former group is reduced about 33-62% and in later group decreased almost 13-30%. Also, the corrosion current density in the samples deposited by gradual change of duty cycle was approximately 0.01-0.04 times of that for monolayer coatings. The microhardness value in the top layers of FGD coating was in the range of 650-800 HV 0.01 which reduced gradually towards the substrate. The high Cr content in the top layers is the reason for high hardness and good corrosion resistance.