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

Abstract

Abstract 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 β* phase, a Widmanstatten α 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 β* and α phases. The nanotwins were formed at the interface of the plate-like β* 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 β* and α phases, while the NiAl precipitates were distributed in the β* 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.