Comparative Hot Corrosion Behavior of New Nickel-Based Superalloy Ad 730 and Inconel 718 in 75 wt.% Na₂SO₄ + 25 wt.% NaCl Molten Salt Medium at 700 °C

The new superalloy Ad 730 is the next-generation material for aircraft turbine disks, but the hot corrosion behavior of this alloy remains to be studied. The hot corrosion behavior of Ad 730 and Inconel 718 was investigated at 700 °C during salt deposition (75 wt.% Na₂SO₄ + 25 wt.% NaCl) and immersion in molten salt. In the deposition test, the thickness of the oxide layer on the surface of Ad 730(5 μm) is about half that of Inconel 718(12 μm). The higher content of cobalt, titanium and aluminum in Ad 730 promoted the formation of protective oxide layers, making better hot corrosion resistance. In the immersion test, the growth of protective oxides was inhibited by the limited oxygen and Ad 730 suffered more devastating damage on its oxide layer on its oxide layer(440 μm), whose thickness is much greater than Inconel 718(93 μm). The additional tungsten, the less content of chromium and the more content of nickel in Ad 730 aggravated acidic fluxing, dissolving the oxide layer.