Microstructural evolution in a spinodal copper alloy and its effect on elastic moduli and hardness

Cu-15Ni-8Sn (wt%) is a high-performance alloy that derives its strength from spinodal decomposition and subsequent ordering. Here, the microstructural changes that occur during ageing are assessed and correlated with both elastic moduli, obtained using resonant ultrasound spectroscopy, and Vickers hardness measurements. Increases in shear modulus and hardness are observed during the initial stages of ageing and attributed to the development of a spinodally modulated structure accompanied by nanoscale D0 22 and L1 2 ordering. With prolonged thermal exposure, discontinuous precipitation of γ and δ phases occurs, associated with a reduction in hardness. Precipitation of γ coincides with a marked decrease in shear modulus, whereas δ precipitation leads to an increase in the shear modulus. The findings highlight the potential of resonant ultrasound spectroscopy for the detection of microstructural changes in this alloy. • Non-monotonic shear modulus variation occurs during ageing of Cu-15Ni-8Sn (wt%). • Spinodal decomposition and ordering lead to a marked increase in shear modulus. • γ and δ phases form by discontinuous precipitation. • γ phase formation associated with a reduction in shear modulus.