Vol . 8 No. 4 August 2000
Materials have a wide variety of applications in aerospace engineering. These materials have to be light, should be able to withstand high temperature and pressure, and provide high strength-to-weight ratio besides being amenable to be manufactured with highly complex aerospace components. DRDO has done pioneering work in this field. Some recent developments of DRDO in the area of aerospace materials are:
Technology of High Pressure Compressor Disc of Aircraft Engine by Isothermal Forging of Titanium Alloy
Isothermal forging is a metal processing technique during which the work piece and the forging dies are maintained at the same temperature throughout the process of forging. The method has found extensive applications in the processing of strain rate sensitive materials, like titanium alloys. Technology of producing high pressure compressor discs of an aeroengine through near isothermal forging of a titanium alloy designed for applications up to 520oC is at advanced stage of development.
Titanium Alloys for Aerospace
The use of intermetallics (Ti Al/TiAl)-based titanium alloys in hotter sections of aeroengine can lead to significant weight saving and increased thrust-to-weight ratio. The intermetallic-based alloys have limited ductility and are difficult to process. DRDO has developed several key technologies, such as melting, forging, rolling and closed die forging at Hindustan Aeronautical Ltd to produce Ti Al-based alloys in various product forms and final components.
Investment Casting Technology
The investment casting technology has been developed for producing state-of-the-art superalloy components for aeroengine applications. The components of Kaveri engine, viz. , high pressure turbine vane (HPTV), high pressure turbine blade (HPTB), low pressure turbine vane (LPTV) and low pressure turbine blade (LPTB) are extremely complex in shape with complicated internal cooling channels. They represent contemporary design and pose a major challenge for manufacturers. The integral stators and rotors for jet fuel starter have also been successfully developed. These components are now qualified for flight and will be incorporated in LCA.
Powder Metallurgy in Aerospace
Various critical components used in aerospace applications are made using powder metallurgy techniques. Several such components have been developed successfully, which have been productionised and integrated into the systems. The application of these components can be outlined as:
Power Absorption Applications. Brake pads for different fighter aircraft, viz., MiG, Hunter, Jaguar, etc. and also for transport and trainer aircraft.
Power Transmission Applications. Clutch discs for helicopters (Mi-4) reconditioned.
Avionics/Accessories. Heavy alloy components in the stall warning system, metallic fuel/airfilter for fighter aircraft.
Brake Piston Insulators for LCA. The insulator pads are mounted on brake pistons for restricting the temperature rise of hydraulic oil during brake application. The insulator pads therefore not only face compressive stresses but are also subjected to high temperature as a result of conversion of kinetic energy during the application of brakes.