Polymer-based coatings are a long-established category of protective coatings for metals and alloys regarding corrosion inhibition. The polymer films can degrade, and when coated on metallic substrates, the degradation facilitates moisture and oxygen penetration, reducing the polymer film’s adhesion to the metallic substrate and exposing the substrate to extreme conditions capable of corrosion. For this reason, pigments, inhibitors, and other compatible blends are added to the polymer coating formulations to enhance adhesion and protection. To prevent the possible deterioration of inhibitor-spiked polymer coatings, inhibitors are encapsulated through diverse techniques to avoid leakage and to provide a controlled release in response to the corrosion trigger. This review discusses polymer-based coating performance in corrosion-causing environments to protect metals, focusing more on commercial steels, a readily available construction-relevant material used in extensive applications. It further beams a searchlight on advances made on polymer-based coatings that employ metal–organic frameworks (MOFs) as functional additives. MOFs possess a tailorable structure of metal ions and organic linkers and have a large loading capacity, which is crucial for corrosion inhibitor delivery. Results from reviewed works show that polymer-based coatings provide barrier protection against the ingress of corrosive species and offer the chance to add several functions to coatings, further enhancing their anti-corrosion properties.

The development of composite/nanocomposite coatings on various surfaces based on electroless process has much interest among researchers due to their enhanced mechanical, electrical, magnetic, and optical properties compared with their metallic or alloy counterparts. These coatings have shown many applications in automotive, aerospace and industrial fields with unique characteristics obtained by the incorporation of secondary particles as reinforcement at micro or nanoscale in the matrix. However, properties of the product depend upon not only the nature of secondary particle used but also the specific characteristics of the metal matrix. This paper critically reviews the recent developments in micro and nanostructured metallic composite coatings formed by electroless coating techniques and retrospect into the various mechanisms of the electroless coating process, its preparation with different metallic systems, properties, and applications in detail.