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

摘要

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 epsilon-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(alpha)-alpha 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 (Delta alpha) and the ratio of generalised fractal dimension D-min to D-max (D-min/D-max) show a remarkable linear negative correlation with HE susceptibility (E-loss). The internal reason was analysed in detail. It is important to note that two linear correlations between the fractal parameters and E-loss 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.