Effect of printing parameters and heat treatment on the crystallinity of PEEK by fused filament fabrication

Polyether ether ketone (PEEK) is increasingly manufactured by fused filament fabrication (FFF) for high-performance applications, yet the local thermal history during printing and subsequent heat treatments can produce large spatial variations in crystallinity and thereby alter thermo-mechanical behavior. A systematic study was conducted to quantify how build orientation, nozzle temperature and post-print annealing affect crystallinity and viscoelastic properties of FFF-printed PEEK. Specimens were printed in three orientations, processed at nozzle temperatures between 380 and 420 °C, annealed at 150, 200 and 250 °C, and characterized by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and high intensity liquid metal X-ray radiation (MetalJet WAXS system). The melting temperature remained essentially unchanged while crystallinity and microstructural ordering were found to be strongly influenced by both print orientation and thermal history. Heat treatment at 200–250 °C reliably increased crystallinity and ordering, nozzle temperature produced a non-monotonic effect on stiffness and damping (410 °C yielded the lowest stiffness and highest damping while 420 °C partially recovered stiffness. These findings indicate that targeted combinations of printing parameters and heat treatment can tailor the coupled microstructure–property relationships of FFF-printed PEEK, including crystallinity, interlayer bonding characteristics, and thermo-mechanical behavior.