SURFACE ENGINEERING The surface characteristics of engineering materials have a significant effect on the serviceability and life of a component, thus cannot be neglected in design. As described by Halling (1985), “Surface engineering can be defined as the branch of science that deals with methods for achieving the desired surface requirements and their behaviour in service for engineering components”. Engineering environments are normally complex, combining loading with chemical and physical degradation to the surface of the component. Surface wear damage is a phenomenon which effects how a component will last in service.

Solid Surfaces A metal may look clean and polished, however the surface microlayers as shown in figure, have been formed due to external factors including machining, temperature and oxide formation.

Why are surface-roughness design requirements in engineering so broad (a) Precision required on mating surfaces, such as seals, gaskets, fittings, and tools and dies. For example, ball bearings and gages require very smooth surfaces, whereas surfaces for gaskets and brake drums can be quite rough. (b) Tribological considerations, that is, the effect of surface roughness on friction, wear, and lubrication. (c) Fatigue and notch sensitivity, because rougher surfaces generally have shorter fatigue lives. (d) Electrical and thermal contact resistance, because the rougher the surface, the higher the esistance will be. (e) Corrosion resistance, because the rougher the surface, the more the possibility that corrosive media may be entrapped. (f) Subsequent processing, such as painting and coating, in which a certain degree of roughness can result in better bonding. (g) Appearance, because, depending on the application, a rough or smooth surface may be preferred. (h) Cost considerations, because the finer the finish, the higher is the cost.

Wear Wear is a process of removal of material from one or both of two solid surfaces in solid state contact, occurring when two solid surfaces are in sliding or rolling motion together.

Surface Modification Techniques Hardfacing Hardfacing is one of the versatile techniquesthat can produce the hard and wear resistant surface layer of various metals and alloys on metallic substrate. A. Hardfacing by Arc Welding B. Hardfacing by Gas Welding C. Hardfacing by Combination of Arc and Gas D. Powder Spraying E Laser Hardfacing Surface Coating Methods Surface coating methods are classified as under: Thermal Spraying (Metal Spraying) Chemical Vapor Deposition (CVD) Physical Vapor Deposition (PVD)