Aerospace and Space industry has widely been a pacemaker for development and introduction of new materials systems and production mechanization in aerospace engineering. The key driving forces for material developments are weight reduction, specific performance improvement, and reduced costs. Application of advanced engineering materials has major impact on both financial and ecological issues.
Polymer matrix composites combine high stiffness and strength with lesser density and therefore extensively used for lightweight structural applications. Aluminium alloys especially overspread cryogenic and common elevated temperature range applications. Fiber reinforcements are used where very high stiffness and wear resistance are required. Titanium alloys are presently used in the temperatures range up to 500-550 degree centigrade. The fiber reinforcement offers dramatically improved strength and creep resistance, while titanium aluminides may well push the temperature limit 200 degree centigrade. Super alloys are capable of service temperature up to 1150 degree centigrade. Long-term space application requires protective coating against hot corrosion and oxidation. Thermal barrier coverings have been imposed to further expand the high temperature range of highly loaded components. Ceramics have seen limited usage so far, but the improvement of damage tolerance by the fiber reinforcement will undoubtedly broaden their applications range at temperatures above 1100 degree in the future.
Aluminium alloys have been used at normal temperature and in cryogenic applications in aerospace engineering, and researchers have focused on the further reducing density, improving the elevated temperature capabilities and the corrosive resistance of the alloys. The polymer matrix composites offer even higher strength at lower density and have, up to some extent, which will replaced metallic materials in specific applications. Titanium alloys are used where lighter aluminium alloys with the no longer meeting strengths, corrosion resistance and elevated temperature requirements. A major effort has been to increase service temperature of titanium alloys. Nearly-alpha type alloys with improve elevated temperature resistance have been introduced and there is more promising are titanium aluminides.
With use temperatures of the order of 800 degree centigrade showing above figure, these intermetallics have the potential to replace Ni-base super alloys. Ni-base superalloys are the prime choice materials in aero-engines, in the environment where the high temperature capabilities and high strength are required. Single-crystal turbine blades represent today’s advanced technology. Despite their potential for high temperature applications, ceramic components have not been introduced into advanced aero-engine design to a large extent, but the future may see an increasing number of ceramics material for structural parts, mainly when reinforced to enhance toughness.
For high strength aluminium alloys many times strength, stiffness and the toughness increase with fall in temperature. Example of low-temperature applications are the aircraft’s operating at heights beyond 12 km (220 K), structures in space (120 K), storage of liquid cryogenic fuels such as oxygen or hydrogen for propulsion launch systems such as Ariane or the space shuttle. Currently, the huge cryogenic aluminium composition is the expendable tank for the space shuttle.
Finally, for many aerospace engineering applications, the values placed on a components cannot be achieved by a one material, but requires a huge materials system where the parts of the structure satisfy different tasks. A prominent example of such a system is ceramic thermal coatings on super alloys in aero-engines. Obviously, improvement of these advanced materials requires a systems approach include the essential, such that the super alloy, and the protective coating that usually comprises a multi layer system.
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