Control of grain boundary connectivity based on fractal analysis for improvement of intergranular corrosion resistance in SUS316L austenitic stainless steel

The connectivity of high energy random boundaries was investigated on the basis of the fractal analyses of grain boundary microstructures in SUS316L stainless steel, to prove the usefulness of a refined approach to grain boundary engineering (GBE) for more precise prediction and control of intergranular corrosion in polycrystalline materials. It was found that the maximum connectivity for random boundary network, termed the maximum random boundary connectivity (MRBC) had a fractal nature in the studied specimens of SUS316L stainless steel. The fractal dimension of MRBC tended to decrease with decreasing fraction of random boundaries, or in other words with increasing fraction of low-energy low-Σ coincidence site lattice (CSL) boundaries. The lower coefficient of variation of grain size distribution suggesting a more homogeneous grain structure, was found to result in the lower fractal dimension of MRBC for the specimens with a similar grain boundary character distribution (GBCD). The optimum grain boundary microstructure for enhanced intergranular corrosion resistance in the SUS316L stainless steel was discussed based on the results from the fractal analyses of MRBC for different grain boundary microstructures.

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