Processing of high purity iridium alloys and effects of impurity elements

摘要

Iridium alloys find use in high-temperature applications due to a unique combination of high melting temperature, elevated temperature strength, and resistance to oxidation and corrosion. Iridium has an FCC crystal structure but exhibits a distinct ductile-to-brittle transition and strain-rate sensitivity common to many BCC metals. Control of trace elements has been shown necessary to obtain the required ductility in the alloys. The purification behavior during electron beam melting is characterized for a wide variety of impurity elements and is shown to be consistent with the Langmuir equation for vaporization in vacuum. The effects of residual impurity elements on mechanical behavior are also discussed. In particular, silicon is found to be detrimental while cerium and thorium have beneficial effects.