Fabrication and properties of a lubrication composite coating based on poly(p-hydroxybenzoic acid) (PHBA)

The present paper describes an approach for fabricating smooth, compact and homogeneous composite coatings of PHBA/PA/MoS₂ on test blocks. The tribological behaviors were tested on a ring-block machine. For the PHBA/PA 6,6/MoS₂ coating of 20 wt.% PA 6,6 and 30 wt.% MoS₂ with the thickness of 20–40 μm, the steady friction coefficient was approximately 0.04 with the lowest wear loss while sliding against AISI 1045 steel ring. The PHBA in coating was synthesized in situ at 200 °C for the first step and 260 °C for the second. The chemical structures and thermal properties of the obtained PHBA were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry/thermogravimetry (DSC/TG). The results showed that the chemical structure of the obtained PHBA was identical to that of the commercial PHBA powder despite that the decomposition temperature and the crystal transition temperature of the former were approximately 10–20 °C lower than that of the latter. The influence of nominal pressure and sliding velocity on the friction coefficient (μ) and wear volume loss of the coatings was investigated. The results displayed that μ increased with the increase of sliding velocity, while it decreased when the nominal pressure was increased. For the volume loss, it increased with both the increase of speed and pressure.