A review of advanced metallic and ceramic materials suitable for high temperature use in space structures

Abstract

Spacecraft, satellites and launch vehicles require efficient, lightweight structural materials. At present, the structural requirements can be largely met by aluminium alloys and polymeric matrix composites based on carbon fibres. However, increasingly there will be a need to specify materials capable of sustaining operational use at temperatures in excess of 250°C and towards 2000°C. Ambitious spaceplane projects such as Hermes, HOTOL, Sanger, HOPE and NASP have highlighted this need. Within the operational temperature band 250°C to 2000°C various metallic and ceramic materials are appropriate for consideration, either in alloy or composite form. This review paper identifies the status of technology on the following: 1. i) Aluminium and titanium alloys and their composites. 2. ii) Superalloys and their composites. 3. iii) Carbon, glass-ceramic and ceramic matrix composites. The development of more weight efficient and thermally stable metallic and ceramic materials has centred on a number of key areas (1). For metallics, improved alloy composition and grain refinement from Rapidly Solidified Powders have given improvements in strength retention at high temperatures (a). The introduction of reinforcements, either particulate, whisker or continuous fibre, have improved the basic alloys by reducing density, increasing stiffness and strength and extending thermal capabilities. Monolithic ceramics possess thermal stability but are inherently brittle and crack sensitive. The addition of ceramic fibres and whiskers has the effect of modifying fracture characteristics by introducing “pseudo-ductility” to raise apparent toughness. In the foreseeable future the emerging high temperature materials will find uses in: Spaceplane substructures and control surfaces; Thermal protection systems and insulation; Propulsion plants and thruster units; Air breathing engines.