Platinum Metals Rev., 1988, 32, (3), 129
Oxidation Resistant Iridium Alloys
A requirement for aerospace components which are capable of serving for sustained periods of time at high temperatures has continued to focus attention on the need for suitable materials, and a recently reported study by K. N. Lee and W. L. Worrell of the University of Pennsylvania has identified iridium-containing alloys as promising high temperature oxidation resistant materials. (“The Oxidation of Iridium-Aluminum and Iridium-Hafnium Alloys at 1550°C and 1640°C”, Extended Abstracts, Electrochemical Society, Spring Meeting 1988, Vol. 88–1, Abstr. No. 281, p. 423)
It has long been known that iridium loses weight at a significant rate when it is heated to temperatures in excess of about 1100°C. Now the oxidation behaviour of arc melted iridium alloys containing 5 to 80 atomic per cent aluminium or hafnium has been examined and it has been shown that the formation of gaseous iridium oxides can be restricted on appropriate alloys by the development of a protective oxide scale on the surface. However, if the amount of the second element is too low, any oxide scale which forms is porous and permits the passage of both oxygen and gaseous iridium oxides.
Iridium-aluminium alloys containing 60 to 80 atomic per cent aluminium form a continuous non-porous oxide layer which shows protective oxidation behaviour even when the alloy is exposed to oxygen at a temperature of 1550°C.