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Influence of Iridium on the Properties of γ′‐Strengthened Co‐Base Superalloys
Author(s) -
Bauer Alexander,
Neumeier Steffen,
Pyczak Florian,
Göken Mathias
Publication year - 2015
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201400266
Subject(s) - materials science , microstructure , superalloy , iridium , solvus , creep , alloy , phase (matter) , metallurgy , volume fraction , precipitation , lamellar structure , composite material , meteorology , biochemistry , chemistry , physics , organic chemistry , catalysis
The influence of iridium on the phase stability, oxidation behavior, and high temperature creep strength of γ′‐hardened Co‐base superalloys is discussed. Ir increases the γ′‐solvus temperature and γ′‐volume fraction since it partitions slightly to the γ′‐phase. However, Ir leads also to a discontinuous precipitation transformation of the metastable γ/γ′‐microstructure into a lamellar microstructure of Co 3 W, CoAl, and a Co‐rich fcc phase for the W‐rich alloys. A reduction of W in presence of Ir leads to a higher phase stability. The constrained lattice misfit between the γ and γ′ phase in the Ir and high W containing alloy is +0.5%. The alloying element Ir strongly increases the creep strength at 850 °C as long as the γ/γ′‐microstructure is not discontinuously transformed. Furthermore, the oxidation resistance is improved by the addition of iridium.