Microwave-Induced Interlayer Bonding of Extruded Polyether Ether Ketone via Calcium–Zinc Ferrite and Carbon Nanotube Synergy

Abstract

Poor interlayer bonding leading to low Z-direction strength remains a major limitation for structural applications of fused deposition modeling (FDM) polyether ether ketone (PEEK). Microwave postprocessing provides a promising noncontact consolidation approach; however, achieving rapid heating while controlling structural deformation and maintaining process control for additively manufactured components remains challenging. In this work, a manufacturing-oriented noncontact microwave postprocessing strategy is developed using a dual-susceptor system consisting of calcium–zinc ferrite (CZF) and carbon nanotubes (CNTs) to enable controlled interlayer fusion of FDM-printed PEEK composites. Processing behavior was systematically evaluated by correlating filler composition with extrusion stability, printability, and microwave response. CNT-only composites exhibited excessively rapid heating that resulted in localized overheating, gas expansion, and structural deformation during irradiation. By introducing CZF into the CNT/PEEK system, a stable and controllable consolidation window was established, enabling rapid interlayer fusion under noncontact conditions (∼500 W, ∼40 s) while preserving macroscopic shape retention. Consequently, the Z-direction tensile strength increased from approximately 19 MPa in the as-printed state to approximately 53 MPa after microwave consolidation, outperforming conventionally annealed counterparts. This work demonstrates a scalable postprocessing route compatible with additive manufacturing workflows for improving the through-thickness mechanical performance of PEEK composites.