Hot Corrosion Behavior of a New Powder Metallurgy Superalloy in Molten Na₂SO₄-NaСl Salts

Abstract:

Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na₂SO₄+5%NaCl salts at 700 °C, 750 °C and 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Experimental results show that the average corrosion rate of Alloy 1 increases as the temperature elevates. The corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr₂O₃, TiO₂, Al₂O₃ , NiO and Ni₃S₂ at each temperature, meanwhile NiCr₂O₄ and Cr₂S₃ appeared at 750 °C and 800 °C respectively. The cross-sectional morphologies and corresponding elemental maps indicate that lots of Ni-Ni₃S₂ eutectic appeared in corrosion layers and a large amount of sulfides and oxides appeared in internal substrate. According to these results, the combined mechanism of oxidation and sulfuration in Na₂SO₄-NaCl salts for Alloy 1 is confirmed. Compared to Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr₂O₃ and Al₂O₃ protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect.

• Periodical: Materials Science Forum (Volume 1072)
• Pages: 57-65
• DOI: https://doi.org/10.4028/p-28w55f
• Online since: October 2022
• Authors: De Lin Liu*, Gao Feng Tian, Yang Chen, Wen Hui Yang, Ren De Mu
• Keywords: Hot Corrosion, Molten Na₂SO₄- NaCl Salts, Powder Metallurgy Superalloy, Sulfuration, Third Element Effect

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