One-step fabrication of amorphous/ITO-CNTs coating by plasma electrolytic oxidation with particle addition for excellent wear resistance

Abstract

As moving machine parts, aluminum alloys suffer from poor wear resistance, however, the combination of amorphous materials and anti-friction lubricant phases has rarely been investigated to improve tribological performance. The amorphous coatings were fabricated by one-step plasma electrolytic oxidation (PEO) with ITO and CNTs addition, of which CNTs were used as lubricant additives to enhance the anti-friction properties of aluminum alloy. It is found that the amorphous phases in the coatings increase with ITO concentration in the electrolyte. As well as, when the concentration of ITO in the electrolyte reaches 40 g/L, XRD cannot detect Al2O3 phase, but only ITO and amorphous phase. The formation of the amorphous coating is due to the fact that In3+ can be used as a network modifier to improve the glass-forming ability of molten oxides and the rapid cooling after discharge. Further, the amorphous coating exhibits a higher hardness (1472 HV0.5) compared to single Al2O3 coatings (267 HV0.5) and its main wear mechanism is adhesive wear with a high friction coefficient (∼0.68). In contrast, with the incorporation of CNTs, the amorphous coating exhibits slight abrasive wear after 6000 sliding cycles under dry friction conditions, with a stable frictional coefficient of around 0.14. Of which, the amorphous coating (1704 HV0.5) serves as a load-bearing and CNT acts as a lubricant phase during friction and wear. Hence, through the synergistic effect of the CNTs additive and the amorphous coating, the tribological properties of aluminum alloy are significantly improved, with a low friction coefficient and shallow wear trace.