Nanotwins-containing microstructure and superior mechanical strength of a Cu-9A1-5Fe-5Ni alloy additively manufactured by laser metal deposition

Laser metal deposition (LMD) additive manufacturing was utilized to fabricate a Cu-9Al-5Fe-5Ni alloy with a hierarchical microstructure and superior mechanical strength. An optimized processing window of LMD was established for printing the alloy with a relative density greater than 99% using laser power of 1000-1500 W, scanning speed of 0.5-1.5 m/min and hatch space of 1.5-2 mm. The LMD-printed alloy exhibited a microstructure consisting of a martensite beta* phase, a Widmanstatten a phase, Fe3Al and NiAl nanoprecipitates, and nanotwins. The hierarchical microstructure comprising microscale cellular structures, sub-microscale grains, and nanoscale precipitates and twins was achieved. The cellular structures were formed by the martensite beta* and a phases. The nanotwins were formed at the interface of the plate-like * phase, which was induced by the low stacking fault energy of the alloy and high cooling rate of LMD. The Fe3Al precipitates were formed within the beta* and a phases, while the NiAl precipitates were distributed in the beta* phase. The yield strength, ultimate strength, and elongation of the LMD-printed alloy were 593-713 MPa, 769-949 MPa, and 10-12%, respectively. The yield strength of the LMD-printed alloy was 160% and 76% higher than that of the counterparts fabricated by casting and wire arc additive manufacturing, respectively, which was attributed to the synergistic effects of the underlying mechanisms including the Hall-Petch type strengthening, dislocation strengthening, precipitation strengthening, and solid solution strengthening. These findings validated the applicability of LMD for printing the Cu-9Al-5Fe-5Ni alloy and facilitated the potential applications in marine and offshore industries.

Automated summary

Laser metal deposition (LMD) additive manufacturing was utilized to fabricate a Cu-9Al-5Fe-5Ni alloy with a hierarchical microstructure and superior mechanical strength. An optimized processing window of LMD was established for printing the alloy with a high relative density and specific microstructure.