Formation of Cu-Ni enriched phases during laser processing of non-equiatomic AlSiCrMnFeNiCu high entropy alloy nanoparticles

Al-rich non-equiatomic high entropy alloy nanoparticles (HEA NPs) were synthesized by ablating Al40(SiCrMnFeNiCu)60 (at%) target in deionized water using nanosecond Nd:YAG pulsed laser operating at a wavelength of 1064 nm and having 8 ns pulse duration. The synthesized NPs have retained the composition and structural phases (B2 type AlFe and Cr5Si3) of the target. The colloidal solution of these NPs was further processed with a 532 nm laser. Upon laser processing, compositional and structural changes in HEA NPs are systematically investigated by using electron microscopy and spectroscopic techniques. The cyclic reheating of NPs during laser processing triggers the formation of Cu-Ni nanoprecipitate over the processed NPs. Owing to their similar ionic sizes and having FCC structural phase, Cu-Ni segregated together during the molten stage and evolve as the precipitate upon solidification. Amongst all the binary combinations of elements present in the HEA NPs, Cu-Ni phases are thermodynamically favored. Based on our experimental results, a possible growth mechanism of Cu-Ni enriched nanoprecipitate is discussed.