Characterization of Precipitates in Cu–Ni–Si Alloys with Different Si Contents by SAXS, SANS, and APT

Abstract

The strength of Cu–Ni–Si alloy can be improved by finely dispersing a Ni–Si precipitate into the Cu matrix by heat treatment. To investigate the strengthening effect of the precipitate, quantitative evaluation of the size distribution and dispersion state is necessary. In this work, we utilized small–angle X–ray scattering (SAXS), small–angle neutron scattering (SANS), and atom probe tomography (APT) to analyze Ni–Si precipitates in Cu–Ni–Si alloys with different Si contents. The APT results revealed two types of diffusion layers at the interface between the Cu matrix and the precipitated phases. Curve fitting of the SAXS and SANS profiles showed that the ratio of the minor axis to the major axis of the precipitates decreased with an increase in aging temperature, and the shape changed from spherical to ellipsoidal. The major axis radius of the precipitates determined by SAXS was measured to be larger than the major axis radius measured by SANS. This is due to the influence of the diffusion layer observed in the APT analysis.