Preparation and Properties of Microarc Oxidation Self-Lubricating Composite Coatings on Aluminum Alloy

Abstract

Microarc oxidation (MAO) coatings were prepared on 2024-T4 aluminum alloy using pulsed bipolar power supply at different cathode current densities. The MAO ceramic coatings contained many crater-like micropores and a small number of microcracks. After the MAO coatings were formed, the coated samples were immersed into a water-based Polytetrafluoroethylene (PTFE) dispersion. The micropores and microcracks on the surface of the MAO coatings were filled with PTFE dispersion for preparing MAO self-lubricating composite coatings. The microstructure and properties of MAO coatings and the wear resistance of microarc oxidation self-lubricating composite coatings were analyzed by SEM, laser confocal microscope, X-ray diffractometry (XRD), Vickers hardness test, scratch test and ball-on-disc abrasive tests, respectively. The results revealed that the wear rates of the MAO coatings decreased significantly with an increase in cathode current density. Compared to the MAO coatings, the microarc oxidation self-lubricating composite coatings exhibited a lower friction coefficient and lower wear rates.

Corrosion and wear resistance of coatings produced on AZ31 Mg alloy by plasma electrolytic oxidation in silicate-based K2TiF6 containing solution: Effect of waveform

“…As a result, the low COF at the initial stage is due to the low real contact surface and the smoothness of the ball surface. By reciprocal ball movement, the roughness and wave peaks created on the ball surface are easily penetrated the surface pores of PEO coating [49] . In this way, a strong mechanical interlocking has happened between the ball and coatings, which increases the friction coefficient until it reaches its maximum value under 3 N normal load [49] .…”

“…By reciprocal ball movement, the roughness and wave peaks created on the ball surface are easily penetrated the surface pores of PEO coating [49] . In this way, a strong mechanical interlocking has happened between the ball and coatings, which increases the friction coefficient until it reaches its maximum value under 3 N normal load [49] . For the unipolar-coated sample, COF is raised gradually up to 0.48, and after a drop, it becomes stabilized in the range of 0.15-0.36.…”

“…Then, the coating is broken and strongly damaged, where the substrate has completely evident after ∼ 30 m distance, then the substrate is worn until 100 m, and the COF of the substrate is recorded. The fluctuation of COF is caused by the uneven distribution of cracks and pores on the surface of the coatings, especially for the coatings produced using unipolar waveform [49] . However, the specimens coated using bipolar and soft sparking waveforms are slightly worn under 3 normal load.…”

Features of Composite Layers Created Using an Aqueous Suspension of a Fluoropolymer

“…Moreover, in general, the thickness of the inner sublayer is much less than the outer porous one. At the same time, due to such a morphological structure, the PEO layer can serve as a good basis for the creation of composite coatings (CC), which make it possible to impart new functional properties to the treated surface, as was presented in [ 3 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ]. In this case, the main promising approach is to fill the pores of the PEO coating with functional materials that have the necessary set of service characteristics.…”

“…One such promising materials is polytetrafluoroethylene (PTFE), a chemically inert, electrically insulating material with antifriction properties and a very wide operating temperature range from −200 to +320 °C [ 71 , 72 , 73 ]. In this regard, the methods of forming composite coatings using PEO and fluoropolymer were considered in various papers [ 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 74 , 75 , 76 , 77 , 78 , 79 , 80 ].…”