Refractry iridium has a unique position among methods due to its resistance to corrosion and its inclination to brittle fracture, the latter only occurring under tension. Since 1960 iridium has been the subject of much research, but this has not lead to an understanding of its inclination to brittle fracture under load, although the problem of working iridium has been successfully solved. Grain boundary brittleness during mechanical treatment is the main problem with iridium, and is a continuing and important topic for academic discussion about iridium. Discussion of this problem, begun forty years age, is continued here.
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