Hexcel HexPEKK 100 is an unfilled polyetherketoneketone (PEKK) powder formulated for laser powder bed fusion (LPBF) additive manufacturing. The grade consolidates at a density near 1.30 g/cm³ and is supplied without carbon fiber or glass reinforcement, which preserves dielectric response and machinability while avoiding the anisotropic electrical conductivity of filled grades. The product is specified for service environments where continuous mechanical loads occur above 100 °C and where exposure to hydraulic fluids, lubricating oils, fuels, and common solvents would degrade polyamide 12 or polyester-based powders. The unfilled chemistry also distinguishes HexPEKK 100 from carbon-filled PEKK grades, which display higher modulus and lower elongation at break, and are not suitable for electrical insulation applications requiring low leakage current.

LPBF processing of HexPEKK 100 uses infrared laser energy to selectively melt powder layers. Published processing conditions for unfilled PEKK powders typically operate with a heated build chamber between 130 °C and 160 °C, a layer height of 100–120 µm, and a laser energy density sufficient to fuse the current layer into the previous layer without boiling the polymer. Hexcel supplies machine-specific parameter sets that include laser power, scan speed, hatch spacing, beam offset, contour strategy, and support interface settings for qualified platforms. Because powder particle size distribution, flow, and infrared absorption vary between production lots, parameter transfer from one LPBF machine to another requires a build validation cube and tensile specimen run, not simple substitution of laser power.

The thermal driving force in LPBF is the difference between the localized melt pool and the surrounding powder bed. For PEKK, this difference is smaller than for PEEK because PEKK melts at a lower temperature; the penalty is that the process window between melting and thermal degradation narrows. Operators monitor melt pool width, surface gloss, and layer-to-layer adhesion using a reference part. In production, batch-to-batch variance in melt flow rate and moisture creates shifts in these indicators. A moisture increase of 0.05 wt% is sufficient to alter melt viscosity and introduce pinholes in thin wall sections. Incoming lots are therefore dried and characterized by differential scanning calorimetry to confirm the melting endotherm onset and enthalpy before use.

Thermal and Crystallization Behavior in Laser Powder Bed Fusion

PEKK is a semi-crystalline aromatic polyketone. The para-substituted phenylene rings and ketone groups produce a glass transition near 160 °C and a melting endotherm typically reported between 305 °C and 315 °C. Compared with PEEK, the crystallization rate of PEKK is slower, meaning that molten layers remain in the amorphous or partially crystalline state for a longer time during cooling. In LPBF, this behavior reduces curl and permits lower build chamber temperatures. Where unfilled PEEK often requires chamber temperatures above 200 °C on production-scale systems to avoid delamination, PEKK can be processed at chamber setpoints in the 130–160 °C range. The slower crystallization is not an unlimited advantage: parts removed too early from the heated chamber may possess an incompletely crystallized core, shifting dimensions and reducing modulus until post-build annealing is completed.

Residual stress generation follows the melt pool cooling path. The laser creates a steep thermal gradient between the localized melt pool and surrounding powder. The solidifying track shrinks while the cooler powder below restricts contraction, forming tensile stress at the top surface and compressive stress in the interior. Chamber preheat lowers the gradient, but thin unsupported overhangs can still peel upward. Support structures must resist the shrinkage forces of the first printed layers; support tips that are too large leave rough surfaces and increase post-machining time. Excessive energy density can also sinter powder outside the intended contour, generating fused debris in narrow channels and blind cavities.

The laser wavelength influences absorption. Polymeric powders absorb differently at 10.6 µm CO2 wavelengths and near-infrared fiber laser wavelengths near 1.07 µm. An off-white or tan PEKK powder may require higher power or an absorbing additive at fiber laser wavelengths, and simply scaling laser power from a CO2 system is not valid. Hexcel parameter sets are qualified against a target laser type, beam diameter, scan head configuration, and inert gas flow field. Changing one of these variables without rebuilding the parameter set can produce unfused powder or overheated melt pools.

Powder handling must address electrostatic charge, moisture, and fines. PEKK powders are less hygroscopic than PA12 but cannot be stored in open containers in an uncontrolled environment. Drying at 120–150 °C for 4–12 h in a desiccant dryer is reported for PEKK powder bed grades, with a target residual moisture below 0.1 wt%. After drying, powder should be transferred under dry conditions; storage relative humidity above 60% can reintroduce moisture sufficient to affect build quality. Powder recovered from the build cake is sieved to remove fused agglomerates and coarse debris and is blended with virgin powder according to a validated recycle ratio. Published data for the maximum permissible recycled content in HexPEKK 100 is limited; users should verify tensile elongation and color stability at the chosen ratio. Dry-blending HexPEKK 100 with PEEK or PA12 powders creates heterogeneous melt pools because the melting point, viscosity, and crystallization rates differ, producing weak interbonds.

On production-scale LPBF systems, powder spreading failures occur when electrostatic attraction between fine particles and the recoater blade leaves streaks or short feeds. Anti-static grounding of hoppers and recoater components is required. If powder flows poorly, increasing bed temperature or lowering humidity may help, but adding free-flow agents is not recommended unless validated by the supplier. Recoater type also changes powder packing. A counter-rotating roller produces a denser powder layer and better contact with the prior layer but can compact powder over thin upward features; a knife blade reduces shear but may leave lower packing density. Parameter sets must be matched to the recoater configuration.

The melt rheology of PEKK is shear thinning, with higher viscosity than PA12 and broadly similar magnitude to PEEK at comparable superheat. In LPBF, the polymer experiences extremely short residence times in the melt state; insufficient time-temperature integration leaves interfacial failure between layers. The zero-shear viscosity is not a direct predictor of coalescence because particle size and surface area dominate initial melting. A shift in melt volume-flow rate measured under ISO 1133-1:2022 between lots should trigger a process parameter review. Powders with a wider particle size distribution can pack more densely but may segregate in the hopper, changing the local melt enthalpy and causing property drift across the build platen.

What Distinguishes HexPEKK 100 From Unfilled PEEK and Polyamide 12 in Service?

The service ranking depends on temperature, ductility, and chemical exposure. HexPEKK 100 retains useful modulus near its glass transition of about 160 °C; PA12 SLS grades lose structural stiffness above 90–100 °C under load. Unfilled PEEK has a lower glass transition near 143 °C but a higher melting point near 343 °C, which can provide a higher short-term use temperature in thin sections. The trade-off is elongation: reported tensile elongation at break for HexPEKK 100 under ASTM D638-14 is approximately 3.5% in the X-Y build orientation and below 2.0% in the Z orientation. PA12 SLS typically exceeds 20% at room temperature, making it more damage-tolerant in snap-fit and impact-loaded brackets.

Chemical resistance of PEKK to aliphatic and aromatic hydrocarbons, hydraulic fluids, refrigerants, and many industrial solvents is superior to PA12 and amorphous PEI. However, PEKK is attacked by concentrated sulfuric acid, nitric acid, and strong oxidizing halogens; sustained steam or boiling water exposure can hydrolyze the backbone and lower molecular weight. Compared with amorphous PEI, PEKK is semi-crystalline and shows improved solvent stress-cracking resistance and higher elevated-temperature stiffness, but lower ductility and a higher processing temperature. Designers replacing metal with HexPEKK 100 in chemical flow paths should test compatibility on printed coupons with the actual fluid mixture at the maximum service temperature, rather than relying on immersion data from molded plaques.

Representative values are shown for initial material selection only. Design allowables must be generated on production-intent machines, with moisture control, recycle percentage, and build orientation held constant.

The lower melting point of PEKK changes the LPBF energy balance. At a bed temperature near 150 °C, the laser must supply less enthalpy to reach the melt compared with PEEK at a bed near 200 °C. This permits lower power or higher scan speed but narrows the acceptable window because the gap between melting and degradation is smaller. Insufficient energy density leaves interlayer voids and powder-particle boundaries; excessive energy density volatilizes low-molecular-mass species, causing pinholes, discoloration, and reduced molecular weight. Stable manufacture requires measuring part density and tensile elongation per lot, not only visual surface quality. Published process capability indices for HexPEKK 100 across multiple machines are limited; internal process capability studies should be performed for each build envelope.

When HexPEKK 100 Replaces PEEK or PEI in Pressurized Fluid Ducts

When a pressurized duct is converted from machined metal or molded PEEK to LPBF HexPEKK 100, the design must account for anisotropic strength. The lowest tensile strength is in the Z orientation, where the layer interface is loaded perpendicular to the build plane. Reported Z-direction tensile strength for HexPEKK 100 is near 75 MPa, approximately 25% lower than the X-Y value. A duct carrying hoop stress should be oriented so that the hoop direction is not parallel to the Z axis; if that is impossible, wall thickness must be increased or the part joined along a plane that transfers stress to the X-Y directions.

Pressure-assisted sintering and layer-to-layer fusion are sensitive to local geometry. Thin walls surrounded by loose powder retain heat, while thick bosses act as heat sinks and can cool the adjacent melt pool, producing voids at transitions. Small liquid-filled channels can exhibit powder entrapment after depowdering; ultrasonic or vacuum-assisted depowdering may be needed, but high-amplitude ultrasonic excitation can crack thin walls in low-elongation PEKK. Threaded inserts and port fittings require separate machining operations. Carbide tooling with controlled feed rates prevents heat-induced microcracking; if coolants are used, machined surfaces must be dried before adhesive bonding. Structural bonding to PEKK generally requires mechanical abrasion or plasma treatment to raise surface energy. Published adhesive bond strength data for HexPEKK 100 in hot-wet pressurized conditions is limited.

Flammability and smoke performance are not automatically guaranteed by the powder. PEKK can meet UL 94 V-0 at limited thickness and exhibits low toxic gas generation relative to halogenated materials, but aircraft interior and duct applications require part-level testing to 14 CFR 25.853 and program-specific smoke and toxicity protocols. The base resin contains no intumescent flame-retardant package; performance depends on the printed part thickness, surface finish, and cell density. Compliance declarations at the powder level do not transfer to the manufactured article, because powder-bed fusion parts may contain microvoids and crystalline gradients that change combustion behavior.

Electrical insulation applications benefit from the absence of carbon filler. HexPEKK 100 is selected over carbon-filled PEKK when volume resistivity, dielectric strength, and stable relative permittivity are required in connectors, standoffs, and sensor housings. Comparative dielectric data should be obtained for the specific build orientation and humidity conditioning, because microporosity and crystallinity affect permittivity and loss tangent. In continuous service above 150 °C, creep under mechanical load must be evaluated because the polymer approaches its glass transition.

Qualification of HexPEKK 100 for production components requires multibatch testing across the intended build envelope. Tensile bars printed in at least three locations—center, left-front, and right-rear—capture heater uniformity and gas flow gradients. The acceptance plan should include density by ASTM D792-20, X-Y and Z tensile strength by ASTM D638-14, and flexural modulus by ASTM D790-17. If density falls below 98% of nominal, process conditions should be corrected before load-bearing parts are shipped.

In-process monitoring records laser power, chamber temperature, oxygen concentration, and recoater torque. A rising recoater torque can indicate powder clumping, electrostatic attraction, or fused debris in the feed zone. A drop in melt pool brightness on the optical pyrometer can indicate shifting powder moisture or laser window fouling. These signals should be trended against tensile property data to define machine-specific control limits. Published Hexcel data for such production control limits is limited; user-generated capability studies are required for critical parts.

After the build, controlled cooling below 100 °C before removal reduces warpage and dimensional scatter. Parts removed hot may warp at internal cavities and lose tolerance. Annealing at a temperature between the glass transition and the melt onset can stabilize crystallinity, but the exact time-temperature profile should be confirmed by differential scanning calorimetry. Under-annealed parts may display property drift during storage; over-annealing can embrittle thin sections.

Fluid compatibility data should distinguish short-term splash exposure from continuous immersion. For splash exposure, PEKK surfaces maintain tensile strength after contact with common hydraulic fluids and lubricating oils; for continuous immersion at elevated temperature, plasticization of the amorphous phase occurs and can reduce the glass transition. Testing should be conducted with the actual fluid mixture, including additives such as anti-wear packages and acidic oxidation by-products. Temperature and stress act together: environmental stress cracking can occur in the presence of organic solvents at stress concentrations. Parts with sharp internal radii and tapped holes are more susceptible than smooth coupons.

Dimensional accuracy is limited by anisotropic shrinkage and laser offset calibration. PEKK parts shrink during cooling from the build chamber, and the Z-direction shrinkage differs from X-Y. Compensated scan files are specific to a machine, chamber temperature, and layer height. Published linear shrinkage values for HexPEKK 100 are not generally available as a universal specification because shrinkage depends on laser parameters, part geometry, and surrounding powder mass. Dimensional validation on a first-article part is required for tolerances tighter than ±0.25 mm. Post-machining of critical interfaces is strongly recommended; printing to final tolerance across multiple batches remains limited by powder lot variation and thermal history drift.