Fractal Analysis of Fractured Surfaces in Cu-9.7 mass% Zn Alloy

Fracture surfaces of Cu-9.7 mass% Zn alloy have been analyzed in terms of the fractal dimension. Specimens with the average grain size of 130 μm were tensile tested on an Instron type testing machine from 300 to 973 K in Argon gas atmosphere. The initial strain rate was 3.5 × 10^-3 s^-1. Microstructure and fracture surfaces were observed by optical microscopy and scanning electron microscopy. The fractal dimension was determined from digitized images of the surfaces using the vertical section method. A ductility minimum appeared at 673 K. Cracks or voids were most frequently observed on grain boundaries of the specimen fractured at the temperature corresponding to the low ductility. There are two kinds of dimension named D₁ and D₂. D₁ represents the void formation and crack propagation, and D₂ represents the effect of grain boundary migration on the void formation. D₁ and D₂ increase with increasing test temperature and the difference between the two values decreases with increasing temperature.