Tribological properties of MAO/MoS2 self-lubricating composite coating by microarc oxidation and hydrothermal reaction

Abstract To decrease coefficient of friction (CoF) of the 6063 aluminum alloy modified by microarc oxidation (MAO) treatment, a MoS2 lubricating layer was synthesized on the MAO coating by hydrothermal reaction. The as-synthetized MoS2 powders demonstrated high purity and interesting micro-spheres structure assembled by many nano-lamellae. The prepared MoS2 layer was ~11 ± 3.3 μm thick, and padded the surface porosity of MAO ceramic coatings. These composite coatings were slidden against GCr15 steel counterparts in air at variable applied loads. According to the results of tribological test, the CoF of MAO/MoS2 composite coatings reduced by ~31.4%, 45.5% and 42.1% compared to single MAO coatings at 2, 4 and 6 N loads, respectively, due to the low shear strength of MoS2. The wear track of MAO/MoS2 composite coatings also displayed more uniform and smoother, causing more stable sliding process. Additionally, the existence of MoS2 layer significantly decreased the wear rate of both coatings and related counterpart balls, implying the enhanced anti-wear properties. Scanning electron microscopy (SEM) and Raman spectrometer revealed that the primary wear mechanism of single MAO coating was a combination of adhesive wear, abrasive wear and oxidation, while the MAO/MoS2 self-lubricating composite coating only showed slight abrasive wear combined with oxidation occurrence.