Cyclic Phase Transition-Assisted Spark Plasma Sintering of AlCoCrFeNi Complex Concentrated Alloys

This paper is devoted to achieving accelerated densification, optimized microstructure, and improved mechanical properties of AlCoCrFeNi complex concentrated alloys (CCAs) by applying cyclic phase transition (CPT) process in spark plasma sintering (SPS) at low temperature. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were performed to correlate the sintering shrinkage with associated microstructural changes. Experimental results show that CPT process promotes the formation of refined intragranular BCC/B2 structure and networked dendritic FCC phase at grain boundaries in the CCAs. The proposed CPT-assisted sintering not only promotes these CCAs to have a fully dense structure that is unobtainable in regular sintering at lower-limit temperature (800 °C), but also promotes these CCAs to have an accelerated densification that does not exist in regular sintering at upper-limit temperature (1000 °C). This better densification outcome is contributed by distinctive elemental redistribution and nano-grain clusters, which promote the mass transfer and the superplasticity behavior in the CCAs. Given this, hardened BCC phase (471HV) and softened FCC phase (188HV) can be obtained in AlCoCrFeNi CCAs after CPT-assisted sintering, which brings a synergistic effect to overcome the strength–ductility trade-off in CCAs. This work is expected to provide more insights into the efficient sintering of complex alloys.