Fractal and multifractal analysis of fracture surfaces caused by hydrogen embrittlement in high-Mn twinning/transformation-induced plasticity steels

A fracture surface is very important evidence in failure analysis after a material fractures under the combined actions of load and environment. In this work, we used field-emission scanning electron microscopy to obtain the morphology of fracture surfaces, which is ascribed to hydrogen embrittlement (HE) for high-Mn twinning/transformation-induced plasticity (TWIP/TRIP) steels with various phase volume fractions of ε-martensite and similar ultimate tensile strengths in the hydrogen-contained environment. The fracture surfaces were then quantitatively characterised by fractal and multifractal methods. The results indicate that HE fracture surfaces of high-Mn TWIP/TRIP steels have obvious self-similar and multifractal characteristics. Moreover, the traditional simple fractal is not appropriate for the complexity of HE fracture surfaces, but the multifractal spectrum f(α)-α and generalised fractal D(q)-q curves show perfect performance in accurately depicting the roughness and homogeneity of such complex fracture surfaces. The width of multifractal spectrum (Δα) and the ratio of generalised fractal dimension Dmin to Dmax (Dmin/Dmax) show a remarkable linear negative correlation with HE susceptibility (Eloss). The internal reason was analysed in detail. It is important to note that two linear correlations between the fractal parameters and Eloss give a good indicator for evaluation of the HE property based on the morphology images of fracture surfaces without multi-step experiments and may be applied in on-site failure analysis of high-Mn TWIP/TRIP steels