Effect of TiB2 Phase and Cooling Rate on Microstructure, Wear and Anticorrosion Properties of AlCoFeNiTiB High-Entropy Alloy

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This paper presents the results of research on the structure and properties of the AlCoFeNiTiB high-entropy alloy (HEA) obtained by two casting methods. Microstructural studies confirmed the formation of the BCC, TiB 2 , and L2 1 phases in the alloy, both in the as-cast state and in the form of plates. Mössbauer spectroscopy showed that in the AlCoFeNiTiB alloy, the iron atoms were mainly distributed in the BCC structure. The paramagnetic properties of the alloys at room temperature were also observed. SEM images revealed the presence of a spinodal decomopsition in the tested alloy in both the ingot and plate forms. Increasing the cooling rate from the liquid state had a positive effect on the corrosion resistance of the alloy in environments of 3.5 and 5 pct NaCl solution. The AlCoFeNiTiB plate in the more aggressive environment showed the best corrosion resistance (polarization resistance of 58.6 kΩcm 2 , corrosion current density of 0.31 μA/cm 2 and the lowest weight loss of 0.0076 mm/year). The results of the electrochemical impedance spectroscopy (EIS) study indicated the beneficial effect of higher cooling rate on the protective abilities of the oxide and hydroxide layer which forms on the alloys surface. The hardness of the rapidly cooled plates (685 HV1) was slightly higher than the hardness of the more slowly cooled ingots (648 HV1), which is likely due to the refinement of the alloy’s microstructure and, consequently, the occurrence of fine grain strengthening. The AlCoFeNiTiB HEA ingot and plate, as well as the AlCoFeNiTi HEA, were described by the same average value of the friction coefficient (0.69); however, the surface morphology of the wear tracks showed a beneficial effect of the TiB 2 phase and the increased cooling rate.