the spray coating of the turbine blades of the moon bound Saturn rocket. Principle of operation Plasma arc welding is an advanced form of tig welding. In the case of tig, it is an open arc shielded by argon or helium, whereas plasma uses a special torch where the nozzle is used to constrict the arc while the shielding gas is separately supplied by the torch. The arc is constricted with the help of a water-cooled small diameter nozzle which squeezes the arc, increases its pressure, temperature and heat intensely and thus improves arc stability, arc shape and heat transfer characteristics. Plasma arcs are formed using gas in two forms; laminar (low pressure and low flow) and turbulent (high pressure and high flow). The gases used are argon, helium, hydrogen or a mixture of these. In the case of plasma welding, laminar flow (low pressure and low flow of plasma gas) is employed to ensure that the molten metal is not blown out of the weld zone. The non-transferred arc (pilot arc) is employed during plasma-welding to initiate the welding process. The arc is formed between the electrode(-) and the water-cooled constricting nozzle (+). A non-transferred arc is initiated by using a high-frequency unit in the circuit. After the initial high-frequency start, the pilot arc (low current) is formed between the elect by employing a low current. After the main arc is struck, the nozzle is neutral or in case of welding-mesh using micro plasma, there can be an option given to have a continuous pilot arc. A transferred arc possesses high energy density and plasma jet velocity. Depending on the current used and flow of gas, it can be employed to cut and melt metals. Microplasma uses current between 0.1 and 10 amps and is used foils, bellow, and thin sheets. This is an autogenous process and normally does not use filler wire or powder. Medium plasma uses current between 10 and 100 amps and is used for higher-thickness plate welding with filler wire or autogenous up to 6 mm plates and metal deposition (hardfacing) using specialised torches and powder feeders (PTA) using metal powders. High-current plasma above 100 amps is used with filler wires welding at high travel speeds. Other applications of plasma are plasma-cutting, heating, deposition of diamond films (Kurihara et al. 1989), material processing, metallurgy (production of metals and ceramics), plasma-spraying, and underwater cutting. Equipment The