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Effectiveness of platinum and iridium in improving the resistance of Ni‐Al to thermal cycling in air–steam mixtures
Author(s) -
Kartono R.,
Young D. J.
Publication year - 2008
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.200804127
Subject(s) - iridium , spallation , materials science , alloy , temperature cycling , spall , metallurgy , aluminide , platinum , intermetallic , bar (unit) , thermal , chemistry , thermodynamics , geology , catalysis , biochemistry , physics , quantum mechanics , neutron , oceanography
The aim of this work was to assess the value of platinum and iridium additions, with and without hafnium, to binary Ni‐Al alloys, intended to act as models for aluminide coatings. Attention was focused on a ( γ + γ ′) Ni‐22Al alloy, but comparisons were made with β ‐Ni‐50Al. All compositions are given in at%. Alloys were exposed to flowing gases at a total pressure of 1 bar for one thousand 1 h cycles at 1200 °C. Compared to binary Ni‐Al alloys, the Pt‐modified alloys performed much better (with or without Hf) in dry air. Thermal cycling in air + 12% H 2 O led to more rapid weight losses, due to enhanced spalling. Again, the addition of Pt was beneficial, but weight losses were still significant in the absence of Hf additions. A Ni‐22Al‐15Pt + Hf alloy slowly lost weight by scale spallation over 1000 cycles, but a Ni‐22Al‐30Pt + Hf alloy resisted weight loss. Partial substitution of Ir for Pt was beneficial in both wet and dry air. However, in the case of wet air, Hf additions were necessary to prevent slow spallation losses.