Improvement of the oxidation resistance of a 5th generation nickel-base single crystal (SC) superalloy through the addition of silicon was attempted. A 5th generation nickel-base SC superalloy TMS-173 (5.6Co-2.8Cr-2.8Mo-5.6W-5.6Al-5.6Ta-0.1Hf-6.9Re-5.0Ru (Ni-bal. mass%)) has excellent creep properties. This was accomplished by increasing the ruthenium content to accommodate the increased amount of rhenium, an element that improves high temperature properties. On the other hand, their additions decrease oxidation resistance.
In this study, silicon was added to modify the oxidation property. However, TMS-173 alloy contains saturated amounts of solution strengthening elements in γ/γ′; therefore, in order to add silicon, tantalum was substituted out to maintain γ/γ′ microstructure. A 50-Cycle oxidation test at 1100°C was carried out to evaluate the effects of silicon, with each cycle lasting one hour. SEM and EDX were used for cross-section analysis.
TMS-173-Ta+Si (5.8Co-2.9Cr-2.9Mo-5.8W-5.8Al-0.1Hf-7.2Re-5.2Ru-1.9Si (Ni-bal. mass%)), showed excellent oxidation resistance; weight loss was much less than that of Rene'N5, and the oxide layer formed was exclusively Al2O3.