Secondary ion mass spectroscopy of impurities in iridium

An Ir blank that had cracked during a deep drawing process and high purity Ir doped with Si or Fe were investigated in order to reveal impurity distributions by means of scanning secondary ion mass spectroscopy. On grain boundaries of the failed blank segregation of C, O, Si, Na, K, Fe, and Cr was found. Poor malleability of the Ir blank is attributed to these impurity segregation effects. A vacuum anneal of 8 h at 1400 °C lead to homogenization of O, C, Na, Mg, Al, Si, K and Ca distributions, whereas Fe and Cr segregation was still pronounced. P and S, also known to cause embrittlement of Ir were never detected. In high purity Ir doped with up to 8×10−3 weight percent (wt.%) Si only faint indications for grain boundary segregation of Si were found. Instead SIMS measurements give evidence of Si clusters in the Ir matrix. SIMS measurements also suggest that concentrations of 200×10−3 to 300×10−3 wt.% may be the onset for Fe segregation to grain boundaries.