Solidification processing and cooling rate effects on hexagonal Co22Cr18Cu20Mn16Ti24 high-entropy alloys

The majority Laves-FCC Co22Cr18Cu20Mn16Ti24 high-entropy alloy (HEA) was studied via electromagnetic levitation processing (EML) to elucidate the effect of cooling rate on the solidification microstructures and phase formation in this alloy. The relationship between the secondary dendrite arm spacing (S-DAS) and cooling rate was utilized to characterize different regions of the solidification microstructures. The cooling rates were determined via the dendrite arm spacing (DAS) equation, DAS=kε−n, with k = 16. The Co22Cr18Cu20Mn16Ti24 alloys were initially made using arc-melting to produce spherical 1.5 g buttons, which were then processed via EML. The molten samples were dropped from either completely molten state, dropped during solidification, dropped during re-melting, or solidified in the magnetic field. Microstructural characterization indicated that depending on the cooling rate, the sample may contain two to four phases. It was found that high cooling rates (≳102 K/s) led to the suppression of the randomly dispersed CoTi-rich dendrites. At slow cooling rates, all four phases were present, while at cooling rates ≳102 K/s, hexagonal dendrites surrounded by FCC interdendritic matrix were seen. Differential scanning calorimetry (DSC) displayed three distinct peaks at 905 °C, 1205 °C, and 1295 °C corresponding to these phases. •Electromagnetic levitation processing was carried out on Co22Cr18Cu20Mn16Ti24 alloy.•Secondary dendrite arm spacing was used to approximate the cooling rates.•Fast cooling rates led to the suppression of randomly dispersed CoTi-rich phases.