Fractal analysis of cyclic creep fractured surfaces of two high temperature alloys

The fractal dimensions of cyclic creep fractured surfaces of two high-temperature alloys (Nimonic 75 and A-286 types) have been measured by using secondary electron line scanning method. All the fractures are intergranular. It is found that the fractal dimensions nearly linearly increase with the increase in fracture strain. The upper limits of measuring units for the linear range of fractal curve are below respective grain sizes. The results indicate that a larger amount of deformation results in a larger extent of irregularity of fractured surfaces caused by the propagation and linkage of intergranular cracks and the distortion near grain boundaries, and hence a higher fractal dimension.