Microstructure and properties of AlCoCrNiFe high-entropy alloy sintered by hot oscillating pressing

In this paper, we report for the first time the successful preparation of bulk AlCoCrNiFe high-entropy alloys (HEAs) by hot oscillating pressing (HOP). The effects of sintering temperature on sintering microstructure, Vickers hardness and corrosion resistance properties of the resulting samples were systematically characterized and compared with samples prepared by conventional hot pressing (HP). The structure of HOPed samples was both FCC and BCC phases (disordered and ordered phases). As the sintering temperature increased, the original particle boundary of HOPed samples was gradually disappeared, and its microstructure uniformity was improved. The significant microstructural coarsening (thickness of phase lamellar increasing) was occurred and the FCC phase volume fraction was increased. Moreover, the density of samples was increased as well. When the sintering temperature was 1100 degrees C, the highest density could be reached up to about 99.23%. Then its maximum Vickers hardness was nearly 488.80 HV1. While the internal defects of the material were reduced because its original particle boundary disappeared and microstructure uniformity improved, which were conducive to the corrosion resistance improvement. Thus, its minimum corrosion current density and corrosion rate in 3.5 wt% NaCl solution were only 1.5 mu A/cm2 and 0.01 mm/year, respectively. The results revealed that the samples prepared by HOP at the same sintering temperature exhibited higher density, fewer original particle boundaries, higher hardness, and better corrosion resistance than the sample prepared by HP. The current study suggests that HOP is promising for making high-quality AlCoCrNiFe HEAs.