The growing interest in environmental sustainability aims to improve resource efficiency and minimize energy consumption throughout material manufacturing, usage, end-of-life handling, and recycling aspect. Energy loss due to friction and wear of materials is the major challenge in machine components. Therefore, reducing friction and improving wear resistance with an appropriate selection of surface materials is the most direct route to reducing energy loss via reduced frictional forces, which contributes directly to sustainable development in the field of tribology and machine components. In that regard, polymer-based materials (PBM) are widely used as load-carrying components, such as bearings in tribological applications. In recent years, additive manufacturing (AM), also known as 3D printing, has gained widespread interest in the functional prototyping of PBM. 3D printing of polymers enables time-efficient processing with weight reduction and energy savings, addressing the sustainable development goals (such as SDG 9, 11, and 12) associated with the manufacturing of engineering materials. Additionally, the ability of in-field fabrication at the time of need increases the potential implementation of decentralized manufacturing with AM, reducing the resource depletion related to logistics and transportation. Therefore, AM/3D printing of PBM holds significant potential to provide a major enhancement to the current manufacturing capabilities with environmental and economic benefits.

Fused filament fabrication (FFF) is an extrusion-based 3D printing technique with increasing popularity for the manufacturing of thermoplastic polymers. The printing technique, processing parameters, material selection, part characteristics, and final application are some of the factors affecting the sustainability and performance of 3D printed PBM. It should be noted that surface finish and internal defects are two of the most important challenges within the FFF method. In addition, the requirement of high thermal processing conditions for high-performing thermoplastic matrices often complicates the processability in FFF. Therefore, this research project aims to identify and optimize the important printing parameters in the FFF method, and to understand the mechanism and formation of internal defects, bulk properties, and tribological performance of 3D printed PBM.

Initially, the key process parameters affecting the quality of 3D printed PBM are identified by employing commercially available filaments. The interrelationship between processing-induced defects and their impact on the material properties is explored. Moreover, novel polymeric composite filaments based on the polyether-ether-ketone (PEEK) matrix are developed in-house. Composite filaments are printed and evaluated as load-bearing components. To develop in-house self-lubricating filaments, microscale short carbon fibers (SCF) and nanoscale silicon dioxide (SiO2) particles are incorporated with the PEEK matrix using melt compounding and fabricated with FFF 3D printing. 3D printed parts are evaluated for their thermal, mechanical, and tribological performance. The characteristics of internal porosity and their impact on the material properties of these composites are investigated in this thesis.

3D printed PBM are examined using fractography and tomography to identify the impact of printing parameters on the bulk structure. Raster angle orientation and printing speeds impacted the location and shape of internal voids. Filament fillers were distributed along the material deposition path during the printing process. Adding micro-SCF in the PEEK matrix negatively influenced the formation of voids and interlayer adhesion, while nano-SiO2 improved the fiber-matrix interfacial bonding, reducing the internal porosity. Moreover, the mechanical properties of 3D printed composites significantly increased compared to neat PEEK. Similarly, the crystallization behavior and thermal decomposition temperatures of PEEK were positively influenced by the presence of fillers. Furthermore, 3D printed components were compared with conventional injection/compression molded samples, and the results showed similar tribological performance for both processing methods.

The experimentally developed self-lubricating PEEK-based composites exhibited significant improvement in friction reduction and wear resistance compared to commercially available filament options. The multiscale composites showed superior tribological performance in dry sliding, exhibiting up to 50% friction reduction and reduction of specific wear rates by an order of magnitude (at 10-7 mm3/Nm) compared to printed neat PEEK. Analysis of wear mechanisms indicated that neat PEEK and SCF‑PEEK suffered severe abrasion and fiber-matrix debonding with increasing contact pressures, respectively. On the contrary, SiO2-SCF-PEEK composites showed improved wear resistance with smoother surfaces due to the polishing effect of nanoparticles and enhanced stress transfer from the matrix to reinforcements. The increased tribo-contact area with a larger polymer sample size adversely impacted friction characteristics with stick-slip, however, the effect on specific wear rates remains remarkably low. Water lubrication effectively improved tribological performance by reducing running-in duration and fluctuations during the evolution of friction coefficients. In this thesis, 3D printed self-lubricating PEEK composites were successfully fabricated and exhibited comparable friction coefficients and wear resistance to their corresponding compression-molded composites. The findings are evidence that FFF 3D printing can be explored as an alternative technique for the sustainable manufacturing of PEEK-based materials for tribological applications.