Novel precipitation and enhanced tensile properties in selective laser melted Cu-Sn alloy

Abstract

The current work reports nano-precipitation and exceptional combination of high strength and ductility in a Cu-13Sn alloy, fabricated by selective laser melting (SLM). The SLM samples revealed competitive unidirectional columnar grains with a fine cellular structure (~600 nm) having Cu-rich spherical nano-precipitates (~3 nm), and δ-phase (Cu41Sn11). Besides, the SLM samples presented a spatially heterogeneous microstructure with both microstructural and chemical heterogeneities in the length scales ranging from micron to nano-scale. The microstructural heterogeneity arises from the heterogeneous grain structure (alternate layers of coarse and fine grains) and dislocation density variations (regions with high and low fractions of low-angle boundaries). Further, the chemical heterogeneity is from the segregation of Sn to the cellular boundaries. The multi-phase hierarchy and spatially heterogeneous microstructure with fine cellular structure significantly contributed to an exceptional combination of high strength and ductility in three orthogonal directions of the SLM processed Cu-13Sn alloy. The back stress due to the heterogeneous structure and the effective stress due to the nano-precipitates, fine grains, and friction stress contribute to realizing exceptional strength. The presence of cellular structure and geometrically necessary dislocations contribute to achieving high uniform elongation in the SLM processed Cu-13Sn alloy. Overall, this work demonstrates the capability of the SLM process in developing novel heterogeneous materials with minimum tensile anisotropy and an exceptional combination of high strength and ductility.