PhDs in year 2015

date: 01.07.2015

In the year 2015 within the Laboratory for Tribology and Interface Nanotechnology dr. Maša Zalaznik defended her PhD thesis titled Tribological properties of PEEK polymers and their composites filled with MoS₂ and WS₂ particles

Dr. Maša Zalaznik: Tribological properties of peek polymers and their composites filled with MoS₂ and WS₂ particles

The thesis presents the effect of MoS₂ and WS₂ particles in the nano and micro scale size on the dry sliding tribological behaviour when used as solid-lubricating particles in PEEK composites. A novel, compression moulding-based technique was used to prepare the PEEK composites, which allows composite manufacturing at much lower temperatures (300 °C), which is below melting. The results are compared with pure PEEK without any particles, and commercial PEEK materials. The results show that all particles, independently on material and size reduce the friction (up to 30%), however, nano scale particles require higher concentration (in analogy to longer time) to form an effective low-friction tribofilm, while MoS₂ and WS₂ particles exhibit similar friction properties. Tribofilm formation is necessary to reduce wear of all composites (up to 51 %), which is greatly promoted with the addition of nano and macro particles of both, MoS₂ and WS₂ materials. Moreover, nanoparticles resulted in even lower wear. In addition, hardness, which is greatly enhanced by the addition of all particles, significantly improves the wear behaviour. However, oxidation of particles during sliding, in particular of WS₂ particles, reduces their beneficial effect on wear behaviour. It appears that oxidation of particles is of key relevance for tribological behaviour, but the detailed effects of size, material and concentration still need further enlightenment.