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The requirements on structural materials for the hot parts of the propulsion of aircraft and spacecraft are extremely demanding. High temperatures, high mechanical stresses, an oxidizing and corrosive environment often act together in a complex way. Well known materials for high temperature applications are nickel base superalloys. Polycrystalline nickel base superalloys are used for discs and blades of aircraft turbines and for rocket engine nozzles. For the hottest parts of modern jet engines, the blades in the first and second row of the turbine, single crystal nickel base superalloys are the materials of first choice. Considerable efforts were made in the last two decades to develop ceramics and intermetallics for use at very high temperatures. Materials often forgotten in the discussion of applications at high temperature are platinum base alloys. Conventional Platinum Base AlloysPlatinum base alloys can be used at temperatures up to 1700 °C. Despite their high prices, their exceptional chemical stability, resistance to oxidation, high melting points, ductility, thermal shock resistance and electrical or thermal conductivity make them interesting for some aerospace applications [1,2]. Platinum alloys are used for nozzles to bring satellites into orbit from the carrier rocket or for nozzles to make trajectory correction. Another important field of application for platinum alloys as structural materials lies in the glass industry. High melting glasses and high-quality glass fibers require the use of platinum-tank furnaces, stirrers and feeders. Pure platinum has only weak mechanical strength at temperatures above 1100 °C. Therefore platinum is usually alloyed with iridium or rhodium [1,3]. Alloying platinum with up to about 20 % rhodium or up to about 30 % iridium increases the stress rupture strength considerably (Fig. 1). The solid solution alloys have good ductility at high temperatures and can be welded to themselves or similar alloys. The common Pt-10% Rh and Pt-20% Rh alloys are absolutely oxidation resistant even at temperatures above 1000 °C. Platinum-iridium alloys show small weight losses after long exposure to high temperatures due to evaporation of the alloying element iridium. Amounts of rhodium or iridium higher than 30 % result only in a small further increase in strength but are accompanied by a great lost in workability. Platinum alloys with more than 20 % of rhodium or iridium are generally so difficult to process that forming operations are possible only at elevated temperatures, and alloys with iridium contents > 20 % tend to embrittle when exposed at intermediate temperatures. Most platinum alloys used are Materials for Transportation Technology. Edited by P. J. Winkler

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