Preparation and Tribological Properties of PI/EP-PTFE Solid Lubrication Coating Filled with ZrO2

Self-lubricating polymer composite coating has excellent frictional and mechanical properties, which improves the surface properties of engine bearing without changing the original properties of the substrate. Due to heavy environment pollution from the electroplate, the plating technology for engine bearing is taking place by polymer coating. The functional filler added into the single polymer coating would improve the mechanical properties such as low friction, wear resistance, high temperature resistance and so on. The tribological properties of PI/EP-PTFE composite coating filled by ZrO2 on the surface of A370 aluminum alloy are studied in this paper. The A370 aluminum alloys were cut into 20 mm×20 mm×3 mm cubes, and they were used as the base material for sand blasting, cleaning and preheating. Firstly, polyimide (PI), epoxy resin (E44), acetone and dimethylformamide were put into a ball milling. Then, different proportions of ZrO2 (mass fractions of 0%, 4%, 8% and 12%) were added and mixed. The uniformly mixed materials were sprayed on the surface of the preheated A370 aluminum alloy surface. The pressure of spray was 0.3 MPa, the distance of spray was (230±20) mm, and the angle of spray was (80±5)°. The sample was obtained after high temperature curing. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the cross-sectional morphology and element distribution of the coating. Then, the two-dimensional morphology and wear volume of the coating wear mark section were analyzed by a three-dimensional optical profiled analyzer (UP-Lambda). The wear trace morphology of the coating was observed and analyzed by optical microscope (SU500). The hardness and elastic modulus of the coating were tested with a nano indentation instrument (Hysitron Ti premier). The frictional tests were carried out on CSM-01 high frequency friction and wear tester. The wear rate of the sample was calculated, and the wear morphology after friction test was observed. With the increase of ZrO2 content, the agglomeration phenomenon becomes worse. The hardness of the coating increases firstly, and then decreases with the increase of ZrO2 content. The wear rate decreases firstly, and then increases with the increase of ZrO2 content under dry frictional conditions at room temperature. When ZrO2 content exceeds 8wt.%, the time of entering the dynamic equilibrium stage becomes longer. The addition of 4wt.% ZrO2 is the best, and the dry frictional coefficient and wear rate at room temperature are 0.09 and 1.01×10‒6 mm3/(N·m), respectively. With the increase of temperature, the frictional coefficient increases firstly, and then decreases. However, the wear rate increases gradually. As ZrO2 content is less than 4wt.%, the coating is mainly adhesive wear at room temperature. When ZrO2 content is more than 8wt.%, the coating is mainly abrasive wear. As temperature increases, furrows and worn tunnels become more pronounced. Under the condition of oil lubrication, the frictional coefficient and wear amount decrease further. After 8 h oil lubrication and 30 min dry friction test, the wear depth of the coating is approximately similar, and the width is different. The non-uniformly softened of polymer materials and ZrO2, agglomeration of large particle materials, viscosity characteristics of lubricating oil under temperature rise, and different friction and contact states are the main reasons, that leads to the above variations of friction and wear. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.