Effects of In Situ Preheating Technology on Mechanical Properties and Microstructure of FFF-Printed PEEK

The Polyether ether ketone (PEEK) suffers from insufficient interlayer molecular chain diffusion and weak interfacial fusion during Fused Filament Fabrication (FFF) due to its high melt viscosity and rapid cooling characteristics, restricting the mechanical properties and engineering applications of printed parts. To improve the interlayer bonding quality of FFF-printed PEEK, an in situ preheating technology integrated into the print nozzle was proposed and implemented. Through a high-temperature controllable preheating system that moves synchronously with the nozzle, local precise heating is performed on the surface of the deposited layer to actively regulate the thermal history of the interlayer interface. Systematic studies on the effect of preheating temperature were conducted. The results show that the influence of preheating temperature on part performance follows a trend of first increasing and then decreasing. When the preheating temperature is 280 °C, the comprehensive performance of the specimens is optimal: the tensile strength reaches 69.47 MPa, which is 21.3% higher than that of the non-preheated reference group; the elongation at break is 71.07%; and the porosity decreases to 8.36%. Microstructural analysis reveals that moderate preheating facilitates molecular chain diffusion and interfacial fusion, whereas excessive heating induces thermal oxidative degradation of PEEK, resulting in deteriorated mechanical performance. These findings confirm that in situ preheating represents an effective approach for enhancing interlayer bonding, thereby offering a practical solution for the additive manufacturing of high-performance PEEK components.