X-ray Analysis of Precipitates Formed in Copper-base Alloys

The formation and growth process of precipitates in Cu-Ni-Si alloys during aging were investigated by anomalous small angle scattering (ASAXS) and X-ray absorption fine structure (XAFS). ä-Ni2Si precipitates with wide nanometer size distribution were formed in the Cu-Ni-Si alloys after a long aging time of 10 s. However, the addition of a small amount of Fe appears to reduce the wide-size distribution of the precipitates in the alloy, resulting in the formation of precipitates with a homogeneous size. XRD measurements were also carried out to analyze microstructural change of Cu matrix after aging. The average size of Cu crystallites in the Cu-Ni-Si alloys without the Fe addition became very large after a long aging time of 10, while no significant change in the average size of Cu crystallites was observed in the Cu-Ni-Si alloys added with Fe. The wide-size distribution of precipitates for the Cu-Ni-Si alloys without Fe is believed to relate to the microstructural change in the Cu matrix. On the other hand, the Fe addition is likely to enhance homogeneous growth of precipitates.