Effect of solidification rate on dendrite segregation and mechanical properties of Cu-15Ni-8Sn alloy prepared by directional solidification

The microstructures and mechanical properties of the directionally solidified Cu-15Ni-8Sn alloy were investigated at solidification rates ranging from 100 to 3000 & mu;m/s. The results showed that the solidification rate significantly affects the phase distribution of the as-cast Cu-15Ni-8Sn alloy. The primary and secondary dendritic spacing reduces and eventually becomes stable as the solidification rate increases. Meanwhile, the size of the primary phase decreases, and its distribution becomes more uniform. The most severe segregation problem of this alloy has been greatly improved. Upon solidification at 100 & mu;m/s, the as-cast Cu-15Ni-8Sn alloy consists of the & alpha;-Cu matrix, & gamma;-CuNi2Sn phase, discontinuous precipitation structure, modulated structure, and D0(22) ordered phases. However, as the solidification rate increases, the discontinuous precipitation structure, modulated structures, and D0(22) ordered phases decrease and even disappear, reducing hardness. As the solidification rate increases, after homogenization treatment, the composition and microhardness distributions of Cu-15Ni-8Sn alloy become more uniform. The time for homogenization is also shortened. It reduces production energy usage and facilitates further mechanical processing.