Effect of Co and Al Contents on Hot Corrosion Resistance of Powder Metallurgy Aeroengine Disk Superalloys

Abstract

Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na2SO4+5%NaCl salts at 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Meanwhile, the hot corrosion tests of Alloy 2 at 800°C were also carried out for comparison. Experimental results show that the corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr2O3, Al2O3 , NiO , Ni3S2 , NiCr2O4 and Cr2S3 at 800 °C. The cross-sectional morphologies and corresponding elemental maps indicate that a large amount of sulfides and oxides appeared in internal substrate. According to these results, the cooperating mechanism of oxidation and sulfuration in Na2SO4-NaCl salts for Alloy 1 is confirmed. Compared with 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. Key words: powder metallurgy superalloy; hot corrosion; oxidation; molten Na2SO4-NaCl salts; sulfuration