Microstructural characteristics and mechanical properties of additively manufactured Cu-10Sn alloys by laser powder bed fusion

Cu - 10 wt% Sn (Cu-10Sn) alloy specimens were additively manufactured by varying the laser powder bed fusion (LBPF) processing parameters, e.g., laser power (200-350 W) and laser scan speed (100-1400 mm/s) at a fixed hatch spacing (0.12 mm) and slice thickness (0.03 mm), to examine their effects on the density, melt pool structure, and microstructure. Microstructural characteristics of the most dense sample were examined using electron microscopy (SEM, TEM) and X-ray Diffraction. The grains in the top-most melt pool layer showed a fanlike structure, whereas all other areas showed small columnar structure aligned nearly parallel to the build direction due to multiple melt-solidification cycles. The high cooling rates associated with LPBF yielded a fine dendritic microstructure, which consisted of primary alpha(1)(Cu) dendrites and a mixture of alpha(2)(Cu) and delta (Cu41Sn11) phases in the interdendritic region. In addition, formation of thin laths (similar to 120 nm) was observed by TEM presumably due to diffusionless martensitic transformation from the high temperature beta phase associated with fast cooling rates. The primary alpha(1)(Cu) dendrite and alpha(2)(Cu) within the interdendritic region contained low (similar to 6.6 wt %) and high (similar to 11.9 wt%) Sn concentration, respectively. Mechanical properties in tension of the dense Cu-10Sn alloy was measured in as-built condition, i.e., sigma(UTS) = 564 MPa, sigma(Y) = 387 MPa, El = 26%; these are significantly superior to the properties determined in previous LPBF investigations and as-cast Cu-10Sn alloy, most likely due to contributions from Hall-Petch and dislocation strengthening mechanisms. Solidification path in LPBF fabricated Cu-10Sn alloy was also revealed from an extensive TEM investigation.

Automated summary

Cu-10Sn alloy specimens were additively manufactured by varying the LBPF processing parameters, and their effects on density, melt pool structure, and microstructure were examined. The results showed that the alloy with high cooling rates had a fine dendritic microstructure and superior mechanical properties. TEM investigation also revealed the solidification path of the LPBF fabricated Cu-10Sn alloy.