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% H2O 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.
OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Cyclic thermogravimetric analysis (CTGA) provided a quantitative assessment of cyclic oxidation kinetics for a Ni-22Al-15Pt + 1 wt.% Hf alloy. This alloy showed a very low extent of oxide spallation and a slow oxidation rate. The adherent oxide thickness calculated from observed weight changes (due to both oxidation and scale loss) was found to be very similar to the directly measured scale thickness. It is concluded that a previously developed description of cyclic oxidation thermogravimetry is applicable, and that the alloy exhibits excellent performance.
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