Effect of heat treatment on hydrothermal aging of CF/PEEK composites

Carbon-fiber-reinforced PEEK matrix composites are exposed to hydrothermal aging owing to their working areas. Therefore, it is important to understand how the mechanical properties of the material change during hydrothermal aging as a design criterion. Firstly, composite samples were quenched to reset their thermal history. Heat treatment (annealing) was applied to carbon fiber-reinforced polyetheretherketone (CF/PEEK) samples at 305°C for 270 min. After quenching. Subsequently, a hydrothermal aging process was applied at 80°C for 45 and 90 days. It was observed that the matrix crystallinity and fiber/matrix interface properties of the CF/PEEK composites changed significantly with the hydrothermal aging and previous thermal history of the material. There was an increase in the degree of crystallinity with heat treatment and hydrothermal aging. The flexural strength values of all materials decreased after hydrothermal aging. However, the decrease in the flexural strength values of the samples with a more amorphous structure after quenching was significantly greater than that in the heat-treated samples before hydrothermal aging. The DMA results show that hydrothermal aging reduces the fiber–matrix interface bond in both quenched and heat-treated materials. On the other hand, the tanδ values of heat-treated samples are much lower than those of quenched materials, as expected. This indicates that the interfacial adhesion was stronger in the heat-treated samples. The test results were supported by scanning electron microscopy (SEM) images obtained from the fractured surfaces as a result of the flexural test.