A Comparative Study on the Hot Corrosion Behavior of Equiaxed Mar‐M247 and Directionally Solidified Mar‐CM247LC Superalloys

ABSTRACT This study compares the hot corrosion behavior of equiaxed Mar‐M247 and directionally solidified (DS) Mar‐CM247LC superalloys at 700°C–950°C under a 75% Na₂SO₄ + 25% NaCl salt coating. Results show that the corrosion resistance of both alloys declines sharply with increasing temperature, a degradation driven by a synergistic oxidation‐sulfidation‐chlorination attack, fundamentally linked to their low chromium content (~8 wt.%). Notably, the DS Mar‐CM247LC alloy exhibits superior corrosion resistance at 800°C. This enhanced performance is attributed to its microstructure; advanced characterization reveals that the elimination of transverse grain boundaries transforms the corrosion mode from a nonuniform, localized intergranular attack in the equiaxed alloy to a more predictable planar corrosion front in the DS alloy. This change, which hinders the primary diffusion pathways for corrosive species, effectively slows the rate of intergranular degradation. While carbide morphology differences offer minor benefits, the control of grain structure is identified as the dominant factor for improving corrosion reliability.