A Study on the Adhesion Properties of Metallic Coatings

Adhesion properties of metallic coatings are always an interesting field of study. Therefore, three most applied pure metallic coatings, which were produced locally, have been selected for this study. Zinc, Nickel and Chromium coatings were purposely chosen for their wide industrial applications. The coatings were prepared on mild steel substrate by means of electroplating. The adhesion properties of these three coatings were compared. In this study, several parameters were studied to establish their relationship with the coating adhesion. These included coating thickness, coating-substrate hardness, coating’s microstructure, substrate’s surface hardness and coating material. Two different coating thickness and two different substrate surface roughness were prepared for that purpose. For the adhesion assessment, scratch testing was applied, using CSM-REVETEST scratch tester. The scratch tests were on the progressive load mode and the critical loads, Lc were determined by both acoustic emission signal and microscopic examination. Surface roughness test was conducted using Mahr Perthometer PGK 120 surface profiler. Rockwell-Hardness tester was utilized for both substrate and composite (coated sample) hardness test. Details, step-by-step procedure of the samples preparation and tests conducted were included. The correlation and relationship between the metallic coatings adhesion and the said parameters were established and highlighted in this report. Generally metallic coatings have improved the surface profile and hardness of the test samples. Eventually, the metallic coatings were technically ranked based on their superiority in adhesion properties. Chromium coating was found to possess the best adhesion properties followed by zinc and nickel.