Fatigue behaviour of age-hardened Cu-Ni-Si alloy and effect of sporadic discontinuous precipitates on fatigue strength

Microstructure and fatigue strength of Cu-Ni-Si alloy with high solute concentrations were studied. The maximum hardness of this alloy was obtained by 0.5 h aging (500°C) and the matrix was strengthened by nano-size δ-Ni2Si precipitates. In addition, some parts of grains transformed into discontinuous precipitates which bring a detrimental effect on mechanical properties, producing a sporadic distribution of discontinuous precipitates. The fatal cracks, which led to the fracture of the specimen, were initiated at the grain boundaries, not at discontinuous precipitation phases. The physical background of fatigue damage is discussed in light of the role of microstructure on the behaviour of fatigue cracks.