Response relationship between loading condition and corrosion fatigue behavior of nickel-aluminum bronze alloy and its crack tip damage mechanism

Corrosion fatigue is one of the major forms for nickel-aluminum bronze alloy used in marine propeller. It is greatly important to understand the corrosion fatigue behavior of nickel-aluminum bronze alloy in seawater for the purpose of improving the service life of marine equipment. In this study, corrosion fatigue crack growth rate of nickel-aluminum bronze alloy in 3.5% NaCl solution was tested under various stress intensity factors, stress ratios and loading frequencies to reveal its corrosion fatigue mechanism. The results show that corrosion environment significantly accelerates the crack growth and decreases the corrosion fatigue threshold, which is attributed to the corrosion reactions between the metals of crack tip and corrosive medium. Among the various factors, loading frequency has more predominant influence on the corrosion fatigue crack growth rate of nickel-aluminum bronze alloy, which can be rationally explained by the hydrogen embrittlement mechanism. Additionally, in the process of corrosion fatigue crack growth, the acidification and the dealumination would occur at the crack tip, resulting in the corrosion dissolution of kappa phases and the deterioration in mechanical properties of crack tip.