Effect of polytetrafluoroethylene gradient-distribution on the hydrophobic and tribological properties of polyphenylene sulfide composite coating

PTFE/PPS composite coating was prepared on stainless steel block by spraying and curing at high temperature. The hydrophobic properties and tribological performances of the coatings were measured with CA-A contact angle meter and evaluated on a ring-on-block wear tester, respectively. Moreover, the worn surfaces of the PPS composite coating and the transfer films formed on the surface of the counterpart ring were investigated by SEM and optical microscope (OM), respectively. FTIR and XPS analyses were performed to detect the element gradient-distribution and chemical changes of the PTFE/PPS composite coating. It was concluded that during the curing process, PTFE macromolecule chain shifted gradually from coating interior to the surface, resulting in fluorine (F) enrichment on the top surface. The gradient distribution of fluorine led to the possession of both good hydrophobic property and strong adhesive strength of the PTFE/PPS composite coatings. XPS analyses indicated that the high shear force led to decomposition and oxidation of the element of S in the PTFE/PPS coating; and the generated active S reacted tribochemically with counterface Fe, atmospheric O and H₂O to form FeSO₄ or Fe₂(SO₄)₃.