Fatigue of precipitate strengthened Cu–Ni–Si alloy

Abstract

The fatigue resistance and tensile properties of a precipitate strengthened Cu–Ni–Si alloy have been investigated. Underaged material exhibited greater work hardening rates than either the peak aged or overaged material. It is proposed that this occurs because the δ-Ni₂ Si precipitates can be cut by dislocations, but the significant difference in structure between the matrix and precipitate requires that interfacial dislocations are left behind which resist further cutting. At and beyond the peak aged condition, an Orowan type strengthening mechanism is believed to operate. Transmission electron microscopy studies of underaged material after both high and low cycle fatigue tests have revealed the presence of precipitate free bands. Such bands are usually attributed to the destruction of the integrity of the precipitates by repeated cutting. In spite of the complex structure of the strengthening precipitate δ-Ni₂ Si and the higher work hardening rate observed in the underaged Cu–Ni–Si alloy, it is concluded that the above mechanism is operative in this material.