Suppression of discontinuous precipitation in age-hardening Cu-15Ni-8Sn alloy by addition of V

Abstract In the present study, the morphology and growth kinetics of discontinuous precipitation (DP) in Cu-15Ni-8Sn-xV alloys were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that the DP colony presents a lamellar structure consisting of alternating lamellae of α-Cu matrix and γ-DO3 phase ((CuxNi1-x)3Sn). In addition, the growth kinetics of DP in Cu-15Ni-8Sn alloy was evaluated using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation and the time exponent can be ascertained between n = 2 and n = 1. It also demonstrates that the initiation of DP in Cu-15Ni-8Sn alloy occurs at grain edges and boundaries. Moreover, the activation energy (Q) of DP is determined to be about 75 kJ/mol by using the Arrhenius equation, thus DP reaction is believed to be controlled by grain boundary diffusion. Interestingly, the addition of V has an obvious effect on the suppression of DP in Cu-15Ni-8Sn alloy. It can be determined that the activation energy (Q) of DP in Cu-15Ni-8Sn-0.2V alloy is about 350 kJ/mol, which is much larger than that of in Cu-15Ni-8Sn alloy. The increasing activation energy of DP after adding V can certainly suppress the formation of DP greatly. Additionally, it is found that a larger number of Ni3V particles generate accompanied by addition of V in Cu-15Ni-8Sn-0.4V alloy. Therefore, the considerable precipitated Ni3V particles impose a strong pinning effect on grain boundary, which also should be responsible for the resultant suppressing effect. Besides, the interlamellar spacing of DP increases and the growth rate of lamellae decreases with increasing V content when aging at 673 K.