Evolution of microstructures and properties of SLM-manufactured Cu-15Ni-8Sn alloy during heat treatment

Due to the aging hardening nature of Cu-15Ni-8Sn alloy, it is necessary to investigate the effect of aging on the properties of SLM-manufactured Cu-15Ni-8Sn alloy. In the present work, first, microstructural evolution of the alloys that underwent the direct aging treatment, solution treatment, and solution treatment plus aging are investigated in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM); and second, mechanical properties and electrical conductivity of these samples were measured. After solution treatment, it's found that fine Sn-enriched precipitates resolved in matrix, an abundance of dislocation diminished, the grain size increased and a number of annealing twins formed. Spinodal decomposition could happen during the cooling of solution-treatment. According to the comparison of the microstructure and performance of the printed sample and the solution treated sample after aging, it's concluded that the strength and conductivity of the aged SLM-manufactured samples are higher than that of the aged solution-treatment samples for same aging duration, however, the plasticity and aging strengthening effect is inverted. The sharp decrement of plasticity is mainly ascribed to network discontinuous precipitations (DPs) in the grain boundary, but not the lamellar DPs. Annealing twin boundaries depressed the formation of DPs in the grain boundary, and improved the plasticity of aged solution-treatment samples. Lamellar DPs were also considered to be enhanced the strength of aged samples, besides modulated structures, D0(22) phase and L1(2) phase.

Automated summary

The effect of aging on the properties of SLM-manufactured Cu-15Ni-8Sn alloy was investigated, showing an increase in strength and conductivity, but a decrease in plasticity. Network discontinuous precipitations in the grain boundary were identified as the main cause for the sharp decrement of plasticity.