Electroless Plating: A Versatile Technique to Deposit Coatings on Electrical Steel

Coatings on grain-oriented electrical steel (GOES) are produced primarily by roller coating deposition of aluminum orthophosphate on the top of forsterite. These coatings provide the insulation resistance and stress to improve the magnetic properties. Electroless deposition of nickel- and cobalt-based coatings could be used as an alternative, because these coatings can be made insulated and stress can be generated and tailored in these coatings. The rate of deposition in electroless plating is faster when compared with other chemical coating techniques, and the process is autocatalytic (no external current required). The coatings are corrosion resistant, and the magnetic properties of the coatings can be varied by simply changing the pH of the solution. Addition of alloying elements, such as phosphorus and boron, can manipulate the stress generated in the coating from tensile to compressive and vice versa. A 2.15 ± 0.15 μm thick Co-Ni-P coating on GOES was able to reduce the power loss by 9%-11%. Similarly, a 414 ± 40 nm thick coating of Co-P-carbon nanotube (CNT) on GOES was able to reduce the power losses ranging 13%-15%. The reduction in power loss in a Co-Ni-P coated sample was due to the tensile stress applied to GOES by the coating that reduced the anomalous loss. The surface roughness was improved for both the Co-Ni-P and Co-P-CNT coatings. An improvement in the surface roughness contributed to the reduction of hysteresis loss.