Effects of 211 and 413 ordering on the corrosion behavior of V-Al-C MAX phases prepared by spark plasma sintering

Abstract

In the present study, two V-Al-C based MAX phases, i.e., V2AlC and V4AlC3 having two types of ordering were successfully manufactured by spark plasma sintering and the corrosion behavior of sintered samples was evaluated. Al, V and C metal powders were mixed with the desired molar ratios by a mixer mill, and sintered at 1300 °C. The relative density calculation revealed almost full densification for both prepared MAX phases. The measurements of mechanical properties showed a low increase in bending strength and Vickers hardness of V4AlC3 compared to V2AlC MAX phase. Evaluation of corrosion behavior of developed MAX phases was carried out in 6.5 M HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. Corrosion current density and corrosion potential of V2AlC (5.3 ± 0.21 μA/cm2 and -0.451 ± 0.01 V, respectively), and V4AlC3 (1.07 ± 0.22 μA/cm2 and -0.091 ± 0.02 V, respectively) were measured and no passivation behavior was observed in their potentiodynamic polarization curves. However, EIS tests at open circuit potential confirmed more corrosion resistance of V4AlC3compared to V2AlC. These tests also revealed the active dissolution of MAX phases in 6.5 M HCl solution at anodic potential of +0.1 V, while the impedance values of V4AlC3 were larger than those of V2AlC. Microstructural investigation revealed the preferential dissolution of V2AlC phase in grain boundaries after corrosion test. Moreover, the layered structure of V2C MXenes was observed in some regions. After corrosion test, V4C3 MXene layers had larger thickness compared to V2AlC. It was found that V4AlC3 with higher amount of Al2O3 and thicker layers has more corrosion resistance than V2AlC MAX phase.