Tribological Properties of 3D Printed SCF/PEI/PEEK Composites

Polymer composites play an extremely important role in the field of high-end equipment technology and complex environmental conditions due to their good self-lubrication, high chemical stability, designability, and excellent load-bearing capacity. Short cut carbon fiber (SCF), as a reinforcing material, is widely used in polymer composites to improve their tribological properties due to its excellent mechanical properties and self-lubricating characteristics. In order to meet the increasing performance requirements of high-performance engineering plastics in aerospace and medical devices, based on the results that polyetherimide (PEI) could improve the thermal properties of poly (ether ether ether ketone) (PEEK), but reduce its wear resistance, the present study was carried out by using the fused deposition molding (FDM) technique as a means of material preparation, and PEI/PEEK as a base material, and SCF as a functional filler. The effect of SCF content on the thermal properties, mechanical properties and tribological properties of PEI/PEEK blended composites was investigated by using SCF as a functional filler. Scanning electron microscopy (SEM) and Raman spectroscopy were used to analyze the transfer film and wear surface to discuss the mechanism of SCF content and load on the tribological properties of the composites. The results showed that SCF as a reinforcing phase can significantly improve the load carrying capacity and wear resistance of polymer composites. On the one hand, SCF with high wear resistance was exposed to the surface of polymer composites during the friction process and takes the load preferentially, which reduced the deformation and damage caused by the dyadic surface to the polymer matrix. Compared with PEI/PEEK composites, the friction coefficients of the composites were reduced by 29.07% and 53.56%, and the wear rates were reduced by 82.4% and 92.28% for the composites with 3% SCF added at 2 MPa and 5% SCF added at 5 MPa, respectively. On the other hand, the addition of SCF helped the polymer composites to form a thin and uniform transfer film on the surface of the metal dyad, which significantly improves the friction reduction and antiwear performance of the composites under dry friction conditions. However, the mechanical properties of the composites were adversely affected with the increase of SCF content, especially for the composites with 15% SCF content. Compared with 30PEI/70PEEK, the tensile and flexural strengths of 15SCF/PEI/PEEK composites had decreased by 58.4% and 31.12%, respectively. Unlike the trend of strength with SCF content, the tensile and flexural modulus of the composites showed a tendency of increasing and then decreasing with the increase of SCF content, and reached the maximum value at 5% SCF content. Compared with 30PEI/70PEEK, the tensile modulus and flexural modulus of 5SCF/PEI/PEEK had increased by 26.73% and 28.81%, respectively. The SCF content had a great influence on the thermal properties of the composites, and the crystallinity of the polymer composites gradually decreased with the increasing SCF content The crystallinity of 15SCF/PEI/PEEK composites decreased by 45.76% compared with that of 30PEI/70PEEK. The residual carbon rate of the polymer composites showed an increasing trend with the increasing of SCF content, and the residual carbon rate of 15SCF/PEI/PEEK composites increased by 12.85% at 800 ℃ compared with that of 30PEI/70PEEK. The results of this study provided theoretical and technical guidance for the design and preparation of PEEK-based friction-reducing and anti-wear composites for service in high-temperature environments.