Cryogenic cyclic aging effect on thermal, mechanical and tribological performance of PEEK-based materials

The impact of cryogenic cyclic aging on the thermal, mechanical, and tribological properties of polyetheretherketone (PEEK) and its composites was investigated to reveal the mechanisms and factors affecting the durability of high-performance materials under prolonged exposure to extreme environments. Cryogenic cyclic aging involved twelve cycles, each consisting of 6-day aging in liquid nitrogen (−196 °C) and 1-day in oven at 40 °C in normal ambient (relative humidity ∼30 %), mimicking operational conditions of cryogenic systems. Tribological tests were conducted using a ball-on-disk configuration with a stainless steel (SS 316L) ball counterface. Tests were performed at 25 °C in air and high vacuum (10⁻⁵ Pa). The thermal stability of the materials was slightly affected. Thermal stresses developed during aging led to polymer embrittlement. Fracture toughness decreased by approximately 22 % after cyclic aging. Abrasive wear increased significantly for unreinforced PEEK, while PEEK composites showed a rise in adhesive wear with prolonged aging. In air, the wear rate increase reached 510 %, whereas in vacuum, some compositions exhibited a wear rate reduction of up to 56 %. • Cryogenic cyclic aging affects PEEK mechanical and tribological performance. • Cryogenic cyclic aging reduces PEEK composites fracture toughness by up to 22 %. • Abrasive wear was increased for unreinforced PEEK; adhesive wear for the composites. • In vacuum, tribological performance of cyclic aged materials was improved.