Effect of stress on grain boundary sulfidation of heat resistant alloys

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A 0.1 μm thick Cr_2O_3 scale formed on an Fe-25Cr alloy in Ar at 973K for 7.2 ks, and then constant loads of 30-40 MPa were applied at 973K in Ar to the specimen. During creep deformation of the specimen the scale cracked at the end of the third creep stage at the grain boundaries, and then propagated into inner grains in the third creep stage. Cracks arrayed perpendicular to the stress loading direction and inter-crack spacings in the grain boundaries on the specimen are shorter than that of in the inner grains. Strain rate in each area is estimated. Inter-crack spacings (L) have power law relations with the creep rate of specimens (ε') as a form of L ∝ (ε')^n. Strain rate exponentη is estimated as -0.44 for the alloy grain boundaries and -0.22 for the alloy grains in this study.