Simultaneously enhanced strength and ductility of Cu-15Ni-8Sn alloy with periodic heterogeneous microstructures fabricated by laser powder bed fusion

Cu-15Ni-8Sn alloy with layer-by-layer periodic heterogeneous microstructures composed of ultrafine equiaxed (~2.6 µm) and coarse columnar (~12.8 µm) grains was successfully fabricated by laser powder bed fusion (LPBF) additive manufacturing. The microstructures were composed of Sn-depleted α-Cu (Ni, Sn) matrix and Sn-enriched γ-(CuxNi1-x)3Sn nano-precipitates. The γ nano-precipitates were found to be mainly uniformly distributed at the melt pool boundaries due to Sn reverse segregation, as though the densely distributed seeds on the surface of a strawberry. The interesting periodic bi-modal microstructure exhibited a simultaneous positive effect on the enhancement of strength and ductility. The yield strength, ultimate tensile strength and elongation at break were (474.04 ± 2.88) MPa, (584.36 ± 4.74) MPa and (14.29 ± 1.78)%, respectively. Remarkable improvements of 12% and 286% in the yield strength and elongation at break were achieved compared with those cast counterparts reported in the published literature. The high dislocations density (~6.78 ×1014 m−2) were the dominant source of high strength and contributed ~49% to the yield strength according to the theoretical calculation. Massive dislocation cells were generated around the γ nano-precipitates during tensile deformation, improving the dislocation storage capacity and the work hardening ability. These findings validated the LPBF printability and the property enhancement of Cu-15Ni-8Sn and provided a promising strategy for the design of high strength and ductility copper alloys through layered precipitation microstructures.