Quantitative unraveling of spinodal decomposition in Cu-15Ni-8Sn alloys via small-angle neutron scattering: Kinetics and strengthening mechanisms

Cu-Ni-Sn alloys are widely used in electrical and other fields owing to their excellent mechanical properties. Spinodal decomposition (SD) plays a critical role in strengthening these alloys. However, its early-stage kinetics and quantitative evolution remain insufficiently characterized by conventional techniques. Here, small-angle neutron scattering (SANS), combined with transmission electron microscopy, is used to resolve the early-stage SD quantitatively and statistically in a Cu-15Ni-8Sn alloy aged at 400 °C. The results show that as aging time extends from 0.5 h to 8 h, the SD wavelength ( λ S D ) increases from 52.1 to 102.9 Å and its amplitude ( A SD ) from 16.6 to 22.3 at.%, following a diffusion-controlled coarsening law λ SD ∝ t 0.25 . Concurrently, L1 2 /D0 22 ordered phases precipitate within NiSn-rich regions. Through quantitative strengthening analysis, it is revealed for the first time that ordered phase strengthening (∼449 MPa) is the dominant mechanism, contributing approximately twice the effect of SD strengthening (∼235 MPa). This work not only demonstrates the unique capability of SANS in deciphering nanoscale phase separation but also establishes a quantitative microstructure-property relationship for designing high-performance Cu-Ni-Sn alloys.