Chapter 8: Thin Solid Coatings

MOSTLY, THE PERFORMANCE OF A MECHANICAL system depends on, to a large extent, surface properties and interfacial behavior of/between its individual components. Especially, in the application of micro/nano tribology, surface behaviors of materials often play a key role in the actualization of designed functions. Techniques of thin solid coatings are extensively used in many fields, which provide desired surface properties by producing thin layers on different substrates. The materials of such layers differ from that of the substrates and their thicknesses are generally in the scale of nanometre to micrometre. Figure 1 gives a typical system of thin solid coating/substrate. By selecting coating materials and deposition methods, desired properties such as low friction, wear resistance, corrosion resistance, etc., could be attained. As one of the most attractive hot spots in material science and technology, research on thin solid coatings has been extensively carried out and the emphasis is generally put on seeking proper coating materials and corresponding preparation techniques. Nowadays, numerous coating materials such as metals, polymers, alloys, ceramics, and their hybrids are available for various applications. As for techniques of coating production, physical vapor deposition (PVD), chemical vapor deposition (CVD), and their derived techniques are extensively used. In the past few decades, some new thin coating materials appeared and attracted great attention. The most attractive coating should be called a diamond-like carbon coating (DLC). With both sp² and sp³ structures, DLC coatings exhibited many excellent properties like low friction coefficient, high hardness, good bio-consistence, and so on, which make it a useful coating material for a wide range of applications. Carbon nitrides are another kind of coating material, on which much attention was paid in the past 20 years. Carbon nitride is practically a material first worked out by calculation. Being claimed possibly to have a bulk modulus greater than diamond, this exciting “calculated material” has attracted great attention since its first prediction in 1989 [1] and considerable research has been directed toward its synthesis as the form of surface coatings.