**Preface to "New Generation Coatings for Metals"**

The world of coatings research is enormous. Coating applications span diverse areas such as nanolayers on single-crystal surfaces to organic coatings for the protection of offshore structures, such as wind turbines and drilling platforms, to heat resistant and self-healing coatings and materials for space applications. The purpose of coatings can probably be divided into two groups, cosmetic and functional. In the former case, the coating simply adds to the aesthetic of the substrate; colored paint for a wall in a house is a good example of a cosmetic coating. Functional coatings serve a purpose other than cosmetic. They can broadly be defined as extending the lifetime of the underlying substrate in a particular environment and under certain stressors. Such examples might include wear-resistant coatings applied to bearings, heat-resistant coatings applied to turbine blades to reduce thermal shock and oxidation in jet engines, corrosion-resistant coatings that prevent metal corrosion, and localized attack on metals. It may also include camouflage coatings where the coating itself disguises the substrate to minimize the risk of physical attack. Stealth coatings would fall into this category. Given the wide range of applications, it is not surprising to discover that there is also a wide range of substrates that require protection through the application of coatings including bio-derived materials, polymers and metals.

The coatings themselves draw from most scientific disciplines such as physics, chemistry, biology, and materials science, adapting many principles from these disciplines for problem-solving in coatings. This brings us to this short book. The reader will not be surprised, given the broad nature of coatings, that the research presented in this book is also of a broad nature. To begin, we look at two papers that investigate metallic coatings on different substrates. Yingying Wang et al. examine AZ91D (a magnesium alloy containing Al and Zn) coatings on steel and magnesium substrates. These coatings are deposited using cold spray technology where the AZ91D powder is accelerated to the target material as high velocity. Cold spray is an emerging technique that shows promise for coating manufacture as well as repair. In the second contribution, Liang Hao et al. use a mechanical plating method to apply Ti-based coatings onto steel balls as part of a wider program of understanding how mechanical plating works. The third paper, by Buchtik et al., explores how improved chemical and physical resistance can be obtained by applying an electroless Ni-P coating to a magnesium substrate. Electroless plating is a chemical process performed in a coating bath. The fourth contribution by Yung-I Chen et al. uses the coatings technique of magnetron sputtering. In this paper, the authors study the structure and hardness of multilayer structures consisting of a 100 nm Cr base layer and a Ru-Zr overlayer.

The next contribution by Merachtsaki et al. examines the corrosion protection of steel using a nanocomposite comprising epoxy and clay nanoparticles modified by organo-ammonium ions. The following paper is an excellent review paper by Taghavikish et al. on ionic and polyionic liquids for corrosion protection. The penultimate paper, by Xiaohui Liu et al., looks at the growth models of plasma electrolytic oxidation (PEO) coatings grown on an aluminum alloy. PEO is another relatively new coating method that promotes oxide formation during the electrical breakdown in an electrolyte. The final paper, by the editor and co-authors, looks at the characterization of the leaching of a new, non-chromate, Li-based inhibitor from a traditional polyurethane-based primer for aerospace applications. In summary, the papers presented in this volume will provide the reader with detailed studies of the breadth and type of work that is being undertaken using a variety of approaches in the field of coatings.
