Adhesion of Trivalent Chromium Coatings on Steel: Assessment by Tensile Testing and AFM Surface Energy Measurements

Hard chromium coatings are widely used for their excellent wear and corrosion resistance, but replacing conventional hexavalent chromium with safer trivalent chromium processes remains limited by adhesion-related issues. This study proposes a simple, quantitative method for evaluating the adhesion of hard chromium coatings deposited on ductile steel substrates using an instrumented uniaxial tensile test. Adhesion is defined as the substrate strain at the onset of coating cracking or delamination, while damage evolution is monitored in situ using optical imaging. Trivalent chromium coatings, produced using four different surface preparation routes, were investigated and compared with conventional hexavalent chromium coatings used as references. Fractographic SEM/EDS analyses were performed to identify cohesive and adhesive failure modes. In parallel, the substrate surface energy prior to coating deposition was assessed using atomic force microscopy via pull-off force measurements. The tensile test successfully differentiated the adhesion performance associated with the different surface preparations. A strong correlation was observed between the critical strain measured during tensile testing and the AFM-derived pull-off forces, highlighting the major influence of substrate pretreatment on coating adhesion. The proposed methodology provides a practical tool for the qualification and optimization of hard chromium coating processes.