Additive manufacturing, particularly Fused Filament Fabrication, has gained significant attraction in recent years. In order to increase the mechanical performances of several components, continuous reinforcements, such as carbon fibers, can be coextruded with a polymeric matrix.The present study relies on a specific 3D printing process, called towpreg coextrusion, which exploits continuous carbon fibers covered with an epoxy resin and polyamide (PA) as the thermoplastic matrix, thus obtaining a 3D printed two-matrix composite. Since polyamide is a highly hygroscopic material, the impact of moisture content on the mechanical properties of 3D-printed continuous composites was investigated. Tensile and flexural specimens were manufactured and tested under both undried and dried conditions. Drying treatment was carried out at a temperature of 70 °C for 2 h in oven, with weight measurements before and after for quantifying weight loss and then the moisture removal. Additionally, through thermogravimetric analysis, the thermal stability of the material was assessed. It was observed that the drying process allows for a reduction of up to 0.56% by weight of moisture in the specimens. Thus, the drying process led to an improvement in the mechanical properties of the material. Specifically, the tests reveal a 15% increase in tensile strength and an 11.5% increase in flexural strength following the drying process, reaching values of 392.78 MPa and 151.06 MPa, respectively. Similarly, an increase in the tensile and flexural moduli was noted in the treated specimens. Finally, fractured samples underwent optical and scanning electron microscopy analysis, through which different fracture mechanisms of the material and the presence of macrovoids and microvoids attributable to the 3D printing process were observed. Knowledge of deposition defects represents an important starting point for the improvement of the process and the mechanical properties obtained to date. This research provides valuable insights into optimizing 3D-printed continuous composites, emphasizing the importance of moisture control for superior mechanical performance in industrial applications.

Additive manufacturing is a promising and emerging technology that can transform the global manufacturing and logistics by cutting costs and times of production. Localized corrosion resistance properties of 0°, 45°, and 90° build-up orientations of 17-4 PH as-sintered samples, manufactured by means of Bound Metal Deposition (BMD), have been investigated by electrochemical and morphological investigations. The cyclic potentiodynamic polarization curves and the open circuit potential monitoring, together with potential drop analysis, revealed that the BMD localized corrosion resistance properties were lowered if compared to a wrought 17-4 PH: a characteristic anodic behavior and many drops in potential were recorded for BMD, whilst the wrought specimens presented a typical passive behavior with pitting corrosion. Morphological investigations by scanning electron microscopy and energy-dispersive X-ray analysis revealed the presence of porosities and defects, especially for the 90° build-up orientation, and inclusions of SiO₂. The 45° build-up orientation showed the best corrosion resistance properties among all the BMD specimens, even though defects and porosities were observed, suggesting that their morphology and geometry influenced the overall corrosion behavior.

The present work aims to study the effect of printing orientation angle and heat treatment on the mechanical properties and microstructure of 17-4 PH stainless steel 3D-printed parts obtained by the binder jetting process to assess the suitability of the process and material for rapid tooling applications. To this purpose, tensile specimens were printed at different printing orientation angles (0°, 45°, and 90°). Half of the specimens were left in the as-sintered condition after the 3D-printing operation, while the other half of the specimens was subjected to H900 heat treatment. Then, tensile and hardness tests were performed to investigate the macro-mechanical properties as a function of the printing orientation angles and postprocessing thermal treatment. Scanning electron microscopy with energy dispersive X-ray spectroscopy was used to observe the fracture surfaces and microscopical defects on the binder jetting printed parts to evaluate the fracture mechanisms. It was demonstrated that printing orientation angles do not affect the mechanical properties of 3D-printed parts, while a significant improvement in the microstructure and mechanical properties is observed after the H900 heat treatment.

The quality, reproducibility, and reliability of additive-manufactured parts strongly depend on optimizing printing parameters and post-processing treatments. This study evaluates the effects on the microstructure and corrosion resistance properties of solution annealing and aging heat treatments performed on 17-4 PH stainless steel samples fabricated with different build-up orientations using a material extrusion technology: the Bound Metal Deposition^TM. The chemical composition and microstructures were determined using X-ray diffraction, chemical etching, optical microscopy, and scanning electron microscopy. The corrosion resistance properties in neutral sodium chloride electrolytes were investigated through cyclic potentiodynamic polarization and open circuit potential monitoring and analysis. The findings demonstrated that the solution annealing heat treatment remarkably enhanced the overall corrosion resistance properties of the samples. The improvement was attributed to the growth of the ferritic phase along the grain boundaries of the martensitic matrix and a finer dispersion of copper precipitates. The aging heat treatment performed after solution annealing enhanced the ferritic phase development, resulting in a further improvement of the localized corrosion resistance properties.