A method for providing a substantially-smooth protective coating on a metal-based substrate is disclosed. It comprises the steps of: (a) applying a thermal barrier coating over the substrate by plasma-spraying; (b) plasma-heating the applied coating according to a time- and temperature schedule sufficient to re-melt the surface region of the coating, allowing it to flow and smoothen; and then (c) cooling the surface region to a temperature below its melting point. The thermal barrier coating is often zirconia-based, e.g., yttria-stabilized zirconia. After being cooled, the surface is much smoother than when originally applied, thereby allowing the coating to be used in a higher-temperature environment.