Recrystallization behavior and mechanical properties of a Cu–15Ni–8Sn(P) alloy during prior deformation and aging treatment

Abstract

The effects of deformation on the aging precipitation behavior, recrystallization behavior and mechanical properties of Cu–15Ni–8Sn and Cu–15Ni–8Sn-0.2P alloys were investigated using scanning electron microscopy, high-resolution transmission spectroscopy, and electron backscatter diffraction. The results showed that during the aging process, the transformation from DO22 to the L12 ordered phase was restrained after cold deformation. However, the coarsening of the modulated structure was promoted. Moreover, the joint effect of discontinuous precipitation (DP) and recrystallization led to the deterioration of the mechanical properties in the late aging stage. The deterioration of the properties caused by DP was much more significant than that caused by recrystallization. Compared to the deformed Cu–15Ni–8Sn alloy, the deformed Cu–15Ni–8Sn-0.2P alloy was more prone to recrystallization reactions. This ultimately inhibited the DP during the aging process. Furthermore, the addition of P in the Cu–15Ni–8Sn alloy improved the peak values of the hardness and ultimate tensile strength, and had a negligible effect on the elastic modulus. The peak-age values of the ultimate tensile strength (yield strength) and elastic modulus of the 70%-cold-deformed Cu–15Ni–8Sn-0.2P aged at 400 °C were 1303 MPa (1280 MPa) and 145.0 GPa, respectively. Nevertheless, our results suggested that the precipitation strengthening, dislocation strengthening, and solution strengthening were the major strengthening mechanisms that improved the yield strength of the Cu–15Ni–8Sn-(P) alloy. The grain boundary strengthening had a negligible effect on the properties of the alloy. Compared to the Cu–15Ni–8Sn alloy, the increase in the yield strength of the Cu–15Ni–8Sn-0.2P alloy was mainly affected by precipitation strengthening.