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Bcc / B2 phase equilibria and phase transformation from B2 to β’ in refractory Nb-X(Pd, Rh, Ir)-Al

  • T. Yamanouchi (a1), S. Miura (a1), M. Ohno (a1) and K. Ikeda (a1)

Abstract

For the improvement of oxidation resistance of Nb-based alloys, PdAl-B2 is expected as Al reservoir for Al2O3 surface layer because it is in equilibrium with Nbss (bcc) phase. However, PdAl forms cracks during casting caused by B2 -> β’ transformation. To suppress B2 -> β’ transformation, Rh, Ru and Ir were chosen as additive elements. It is found that bcc / B2 two-phase field in Nb-Pd-Ir-Al system is limited to be small fraction of Ir, while (Pd,Rh)Al-B2 is in equilibrium with bcc solid solution in a wide composition range and addition of Rh prevents occurrence of B2 -> β’ transformation. Composition range of (Pd,Ru)Al-B2 in equilibrium with bcc phase is wider than (Pd,Ir)Al-B2 but narrower than (Pd,Rh)Al-B2. Rh and Ru addition are also beneficial for improving eutectic temperature of Nb-bcc / B2 aluminide two-phase alloys.

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Keywords

Bcc / B2 phase equilibria and phase transformation from B2 to β’ in refractory Nb-X(Pd, Rh, Ir)-Al

  • T. Yamanouchi (a1), S. Miura (a1), M. Ohno (a1) and K. Ikeda (a1)

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