The structure and mechanical properties of a multicomponent alloy of the Al-Co-Cr-Cu-Fe-Ni system obtained by quenching from the melt

This study investigates the influence of cooling rate on the microstructure, phase formation, and mechanical properties of the high-entropy alloy (HEA) Al4CoCrCuFeNi. X-ray diffraction analysis revealed a fascinating interplay between cooling rate and phase composition. The as-cast sample exhibited a coexistence of an ordered BCC (B2) phase and a disordered BCC phase, suggesting the presence of diffusion processes. In contrast, the melt-quenched sample displayed a single B2 phase, highlighting the suppression of diffusion at high cooling rates. This observation aligns with theoretical predictions based on thermodynamic, electronic, and atomic-size criteria. The microstructural examination further verified these findings. The as-cast sample displayed a characteristic dendritic structure, while the quenched sample exhibited a finely dispersed morphology, likely due to the formation of a planar crystallization front during rapid quenching. The microhardness measurements showcased a remarkable enhancement: the quenched HEA achieved a value of 9400 MPa, significantly exceeding the 6500 MPa of the as-cast sample. This improvement can be attributed primarily to the increased presence of the harder B2 phase in the quenched sample. Additionally, the quenched microstructure, characterized by a higher level of microdeformations and smaller grain sizes, likely contributes to the observed increase in hardness. In conclusion, this study underscores the critical role of cooling rate in tailoring the phase composition, microstructure, and ultimately, the mechanical properties of Al4CoCrCuFeNi HEA. Rapid quenching promotes the formation of a harder B2 phase and a more refined microstructure, leading to a significant enhancement in microhardness. These findings offer valuable insights for optimizing the processing techniques of Al4CoCrCuFeNi HEA to achieve desired mechanical properties for various applications.