Fractal fracture and transformation toughening in CuNiAl single crystal

The fracture toughness J _Ic (ρ) and fractal dimension D _f of fractured surfaces of CuNiAl single crystal have been measured at temperatures in the range 20 °C to 120 °C, in which thermoelastic martensitic transformation takes place. The parent phase has higher fracture toughness than the martensite phase due to stress-induced transformation. The relationship between J _Ic (ρ) and D _f has been studied. It was found that log J _Ic (ρ) is linearly related to D _f if the failure involves a single mechanism. The slope of the plot may either be positive or negative for brittle or ductile failure, respectively. The difference in the J _Ic (ρ)-D _f correlation can be understood in terms of the micromechanism of fracture.