Abstract
The present study investigates the influence of hygrothermal ageing on the tribological behaviour of polytetrafluoroethylene (PTFE) polymer composites. Three PTFE composites along with unfilled PTFE were tested in sliding contact against Inconel 625 (a Ni-based alloy) plates in both dry and water-lubricated conditions, utilising a unidirectional pin-on-disc tribometer. The tribo-tests were performed at a constant sliding speed of 0.13 m/s with a normal load of 84N providing an apparent contact pressure of 5 MPa. Hygrothermal conditioning was carried out at two different temperatures, and the water absorption evolution and kinetic parameters were estimated. Various characterisation methods were used to identify the wear mechanisms and influence of hygrothermal ageing on the degradation of the filler/matrix. The different tribological behaviour for different PTFE composites was observed within the ageing timeframe. The wear resistance of the fibre-filled samples was reduced compared to the non-aged ones over the ageing timeframe. However, the friction and wear resistance of the bronze-filled PTFE were enhanced by hygrothermal ageing.
Highlights
Used mineral and synthetic oils in hydropower plants pose concerns because of fear of spillage and downstream contamination
The friction force and the wear depth of polymer pin were continuously measured with a strain gauge force transducer and a displacement sensor, a linear variable differential transformer (LVDT), which was sequentially coupled to the pin holder
The results show a great reduction in the bronze-filled PTFE aged for 132 days at 80 ◦ C, which can be attributed to the oxide layer formed on hydrophobicity of bronze-filled PTFE aged for 132 days at 80 °C, which can be attributed to the oxide the specimen
Summary
Used mineral and synthetic oils in hydropower plants pose concerns because of fear of spillage and downstream contamination. Due to increased environmental concerns, the hydropower industry has strived actively for alternative lubricants to replace oil-based lubricants within their facilities. Oil-free plants are being introduced by replacing conventional lubricants with water. This solution presents challenges regarding material selection. The use of polymers and their composites in tribological applications arises from their favourable bulk and surface characteristics [1,2]. Polytetrafluoroethylene (PTFE) and its composites are appealing in load-bearing tribological applications due to their corrosion resistance, low dynamic friction in sliding against metal surfaces under certain conditions, and low water absorption [3]
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