A review on physical vapor deposition-based metallic coatings on steel as an alternative to conventional galvanized coatings

An effective way to protect the steel surface from degradation is to develop a coating on top of the steel substrate. A wide variety of coating deposition processes are available to develop protective coatings on steel. To date, several processes like hot-dip galvanization (HDG), electrogalvanization (EG), and physical vapor deposition (PVD) have been investigated. Among them, the most commonly used methods are hot-dip galvanization and electrogalvanization. HDG is used extensively due to lower cost, shorter process time, the requirement of lesser maintenance, uniform protection, and ease of deposition at a larger scale. On the other hand, EG promises in providing advantages like versatility in the coating composition, good surface finish, uniformity in the coating, lower coating thickness, etc. Although both processes provide different advantages, there are always drawbacks limiting their applications. To overcome different limitations of conventional processes and for further advancement of protective coatings, PVD has received increased attention in recent years over hot dipping and electroplating. PVD process provides a more uniform deposit, higher accuracy, very low thickness, improved adhesion, a wider choice of materials, and no environmental pollution. In this paper, we review the scope and prospect of the PVD technique for the steel industry over HDG and EG. The paper focuses on different kinds of PVD techniques, their advantages, and disadvantages. An emphasis has been given to the recent development of Zn- and Al-based PVD coatings on steel substrates. The industrial competency of PVD in the steel industry has been discussed in this article. Challenges associated with the commercialization of the process and recommendations for further improvement have been discussed.