Ceramic/fluoropolymer composite coatings by thermal spraying - a modification of surface properties

Even if polymer coatings are widely used for industrial applications, their performances are often limited by a poor scratch resistance or a high water and gas permeability. To overcome such limitations, the composite coating of ceramics with polymer can be a solution to be adopted. Thermal spraying may help to achieve this objective, thanks to its ability permitting to deposit many kinds of materials with an important range of coating thicknesses. The aim of this paper is to develop composite coatings (fluoropolymer/ceramic) by plasma spaying. Due to different thermal characteristics of the initial materials (PTFE or PFA polymers and Al2O3-TiO2 ceramic), three types of powders injections are elaborated. To compare these three conditions, microstructure, surface wettability and wear resistance deposits behaviour were characterized. Al2O3-TiO2/fluoropolymer (PTFE or PFA) composite coatings are characterized by a well-melted ceramic matrix in which rounded polymer particles are randomly distributed. The as-sprayed polymer particles kept at the coatings surface can however be spread thanks to a thermal treatment at 350 degreesC during 15 min. Unlike the PFA, a large PTFE loss was noticed during the spraying process. Thus, the highest polymer/ceramic ratio is observed in the coatings made with the separated injection of the Al2O3 - TiO2 and PFA powders. The lowest friction coefficient is also measured for this coating. (C) 2004 Elsevier B.V. All rights reserved.