Comparative study of the microstructure evolution of dual-phase Al-Co-Cr-Fe-Ni high-entropy alloy prepared by direct laser deposition and vacuum arc melting

摘要

Dual-phase (FCC + BCC) Al0.7CoCrFeNi high-entropy alloys were successfully fabricated by direct laser deposition (DLD) and vacuum arc melting (VAM). It has been found that there is a significant difference between the microstructures produced by the two methods. A hypoeutectic structure (primary FCC phase + lamellar FCC-BCC eutectic microstructure) was observed in the DLD sample, while BCC phase in the VAM sample displayed basket-weave-like structures by spinodal decomposition, which can be attributed to the different thermal gradients and cooling rates for the two processes. A higher percentage of FCC phase was found in the DLD sample (63 %), compared to the VAM sample (55 %). In both samples, FCC phase was rich in Fe, Co and Cr, whereas Al and Ni were segregated in BCC phase. Furthermore, chaotic grain orientations were observed in FCC phase in both samples. A strong (001) texture along the direction of solidification was formed in BCC phase in the VAM sample, while in the DLD sample the texture showed a deviation from (001) orientation because of the complex nature of the temperature field.