Environmental effects on the sliding behaviour of PEEK composites

The sliding performance of PEEK materials against steel discs was investigated in air, vacuum and hydrogen environment. PEEK compounds were filled with graphite flakes, CNTs or TiO2 particles. Results indicate that pure PEEK is environmentally sensitive. Desorption of gases in vacuum leads to weakening of the polymer, inducing high wear rate in vacuum condition. Very low friction is obtained with composites containing graphite and CNTs in hydrogen (0.04), while the lowest wear rate is achieved with the addition of TiO2 particles both in vacuum and hydrogen environments. Chemical processes occur within the materials and at the tribocontact, and interact with each other. In particular, the formation and adhesion of a thin and homogeneous transfer film strongly depend on the environments.