prabha haran

The development of cladding (also called as hardfacing coatings) as a surface treatment is technologically significant in many industries like aeronautical, automotive, agricultural, Power Plants etc. The conventional surface coating techniques such as Physical Vapor Deposition (PVD), Chemical Vapour Deposition (CVD), Thermal Plasma Spraying, Electro deposition, Carburizing, Nitriding, Flame Induction Hardening, Galvanizing Diffusion coating offer many limitations like High processing time, high heat input energy, high material consumption, lack of flexibility, poor precision and lack in scope for automation. But surface engineering techniques using laser as source energy are free from these limitations. Also they have advantages over conventional welding metal deposition Gas Metal arc welding (GMAW) Gas Tungsten Arc Welding (GTAW) is the smaller dilution zone which in turn produces a smaller Heat Affected Zone (HAZ). Further laser cladding provides with more dense coatings, metallurgical bonding with substrates and minimal thermal distortion in the processed parts as compared to other more standard deposition methods. In addition to these advantages, the laser cladding process, as a method of hardfacing, is used to increase the wear, abrasion, corrosion and oxidation resistance and or at higher operating temperatures and impact performance of metallic components. One of the major benefits associated with laser cladding is the ability to finely control the heat input. With the continuous developments, the present technology on this process is employed to produce Laser Cladding with Metal Matrix to deposit hard facing coatings on metallic surface subjected to high abrasive wear and corrosive atmosphere. The hardfacing material consists of a mixture of hard, reinforcing phases immersed in a ductile metal/alloy matrix. The reinforcement constituent is normally a ceramic or a compound of a refractory metal as titanium, tungsten or chromium carbides or Nitrides and Borides. The matrix is usually a Nickel or Cobalt or alloy based on these elements which further enhances the layer resistance to corrosion, particularly at elevated temperatures. The mechanism of producing hard and wear resistant microstructure is that uniform distribution of hard and fine particles in a ductile matrix results in considerable improvement in wear resistance. Such a composite microstructure combines advantages of both the hard but brittle ceramic particles and the soft but ductile metallic matrix. This microstructure if produced into a surface layer of a component enhances wear life of that component. This review work focusing on this modern laser cladding techniques, studies the deposition of ductile material like Nickel (Ni) and Chromium (Cr) based composite layers on Carbon Steel/Martensitic steel (substrate). Nickel/Chromium alloy matrix, comparatively ductile provides toughness, ductility, corrosion and impact resistance whilst being wear resistance at elevated temperatures. More commonly Tungsten Carbide ceramic material is used as hard substance since it has outstanding physical and chemical properties compared to other commonly used ceramic materials. Tungsten Carbide (WC) has high melting point (3410º C), high hardness, low thermal expansion and good wettability by molten metals and alloys. The fine control of the heat input allows the matrix to be completely melted and alloyed to the substrate surface (Base Metal), whilst at the same time, the ceramic particles are distributed evenly throughout the matrix giving an extremely hard, wear and corrosion and impact resistant coating. Also, optimum conditions to obtain dense, uniform carbide distribution and hardness close to nominal values will be defined. Following objectives are generally achieved through optimization of the laser cladding processes. Effect of heat input on the Heat Affected Zone (HAZ) Characterization of Microstructure Micro Hardness Bead Geometry parameters Correlation between the various influencing parameters The effect of Nickel/Chromium content with respect to microstructure, susceptibility for cracking and the wear rate of the resulting coating.