The manufacturing process of blades includes forging, followed by machining, pickling, and the blades then undergo stabilised tempering after achieving its geometry. The product is then inspected through non-destructive techniques. The inspection techniques include magnetic particle inspection, zyglo and ultrasonic tests. After inspection, the material undergoes vibro-tumbling of profile, which is then followed by the root strain hardening. The blades are then plated. The plate process is typically welding process; the blades are plated with rotor through welding. The plating of the root of blades is conducted with silver plating. The plating of aerofoil is conducted through nickel-cadmium plating; the plates are then annealed through thermal diffusion. The intent of plating i.e. the material build up is to prevent fretting fatigue. The plating offers "cushion effect and lubrication, the root of the blade is plated with silver 3-6 micrometer thickness" (Bruce, 1997).
The machining process has been further advanced, and the electrical discharge machining process is commonly employed. This process is thermal process, the electrode is melted and vaporised. The process is common for the construction of the blades. The materials which commonly undergo electrical discharge machining include titanium alloys and nickel-based super alloys. The surface integrity and the wear resistance of the base material is protected through electrical discharge machining (Mikell, 1996). Under this process, the surface integrity is protected through application of surface alloying during the process of sparking; this is possible by pouring metallic powders in the dielectric. The powders of following material i.e. graphite, aluminium or silicon are also common for the generation of surfaces with reduced cracks.
The application of partially sintered electrodes offer reliable surface finishing against application of conventional tool electrodes under standard polarity. The application of the negative tool polarity is common, "the electrodes including Al, Cr, Cr/Ni, Cu/Co, Cu/Mn, Cu/Sn, Cu/W, Ni, Ni/Co, Ni/Fe, Ni/Mn, Ni/Si, Ti, Ti/A1, TiC/Ni, W/CrC/Cu and WC/Co are used" (Kalpakjian, 1997).
The blades and nozzles of gas turbine are exposed to high temperature. The metallurgy for this machine is therefore critical, and vulnerable to high creep factor. The technology and research has evolved the material which is resistible against the extreme conditions of the gas turbine. The material preferred for the construction of the gas turbine blades and nozzles include cast nickel-base super alloys. The complicated coring technology is used to develop cooling passages for the blades. The metallurgy has simplified and advanced the manufacturing process, the process includes directional solidification and single crystal techniques.
The certain failures associated with the blades and their weld joint can be prevented through implementation of the non-destructive tests. The cracks with the metallurgy and weld joint can be prevented by improving the shape to influence the dynamics of the assembly. The "electro-corundum blasting in place of sand blasting will eliminate the possibility of silica entrapment" (Thyer, 1991).