The austenitic stainless steels utilized in the production of osteosynthesis devices are susceptible to crevice corrosion. Several studies have compared the corrosive behavior of austenitic and duplex stainless steels (DSS), both of which are recognized as viable biomaterials for tissue engineering applications. All of the in vitro and in vivo studies on animals and clinical results reported to date indicate that austeno-ferritic duplex stainless steel can be recommended as a suitable alternative to ASTM F138 steel, since it is resistant to crevice corrosion in the human body and presents superior mechanical properties. The use of DSS for biomedical applications is still under discussion, mainly due to the lack of knowledge of its behavior in terms of device heating or induced movement when exposed to magnetic fields, a potentially harmful effect for the human body. As a breakthrough production technology, additive manufacturing (AM) has demonstrated significant benefits for the fabrication of metal devices with patient-specific geometry. Laser powder bed fusion has particularly been used to manufacture DSS-based components. A fine control of the processing conditions allows for an understanding of DSS microstructural evolution, which is essential for selecting processing parameters and estimating performance, including mechanical properties and corrosion resistance. Furthermore, scientific investigation is necessary for determining the relationships among material, process, and magnetic properties, in order to establish the underlying principles and critical responses. The purpose of this review is to highlight the key performances of DSS for biomedical applications and to point out the relevant role of advanced processing technologies such as additive manufacturing.

Metal additive manufacturing (AM) technologies can be classified according to the physical process involving the raw material as fusion-based and solid-state processes. The latter includes sintering-based technologies, which are aligned with conventional fabrication techniques, such as metal injection molding (MIM), and take advantage of the freeform fabrication of the initial green part. In the present work, 17-4PH stainless steel samples were fabricated by material extrusion, or rather bound metal deposition (BMD), a solid-state AM technology. The powder-based raw material was characterized together with samples fabricated using different angular infill strategies. By coupling different characterization technologies, it was possible to identify and classify major properties and defects of the raw material and the fabricated samples. In addition, microstructural modifications were found to be linked with the mesostructural defects typical of the BMD solid-state additive manufacturing technology applied to metals.

Lattice are porous structures obtained by a controlled repetition in the space of a designed unit cell, resulting in reduced weight and unique functional characteristics such as high specific strength and stiffness, mechanical energy absorption, and heat transfer control. This work aims to tailor geometrical variables and process parameters to fabricate L-PBF Inconel 718 beam-based lattice structures, focusing on their novel use as support structures during the printing process of metallic components, enhancing structural integrity and heat dissipation. 3D models of different porous structures (cell type: FCC-Z) were developed varying geometrical parameters. Finite Element Method simulations were conducted by Ansys, validating its ability to meet quality standards for directional deformations and residual stresses. The simulation’s correlation with the coordinate measuring machine (CMM) analysis confirmed the accuracy of the model. Scanning electron microscopy (SEM) characterization was employed to analyze the deformation and failure characteristics of the lattices, excluding those with geometric parameters unsuitable for optimal support performance. Microstructural analysis revealed partial recrystallization in the heat-treated samples. The remaining dendritic structures indicate incomplete homogenization, particularly near the lattice. Precipitated strengthening phases such as γ′ and δ were identified, alongside minor quantities of η phases and MC carbides, which could influence ductility and strength. Vickers microhardness tests showed higher hardness in the heat-treated samples, particularly at nodes and struts, with a more uniform hardness distribution in heat-treated samples due to the precipitation of strengthening phases. This highlights the role of heat treatment in enhancing the material’s mechanical properties. Graphical Abstract

The creep response of the 17-4PH precipitation hardening steel produced by a new additive manufacturing technology (Bound Metal Deposition) was investigated at 482 °C (900 °F), under stresses ranging from 350 to 600 MPa. Two different sets of samples produced with different deposition parameters were considered. Prior heat treatment consisted of ageing either at 482 °C (state H900) or at 621 °C (H1150). The minimum creep rate and time to rupture dependencies on applied stress were obtained. The creep response in terms of time to rupture under a given stress, in particular, was compared with the only other available literature dataset on a similar steel processed by traditional technologies. The analysis of the experiments demonstrated that the presence of dispersed defects causes, in the Bound Metal Deposited steel, a substantial reduction (35–40%) of the creep strength.

Laser Powder Directed Energy Deposition (LP-DED) is an advanced additive manufacturing process that uses a focused laser beam to melt and fuse powder material onto a substrate. This technology enables the production of complex metal components with high precision and material efficiency. The properties of the powder feedstock are highly important and have been extensively studied in the literature. Powder size distribution and particle shape have been identified as key factors influencing the flowability, and it is imperative that nozzle designs take these into account for optimum material delivery. The laser–powder interaction, where the laser energy influences the melting behavior, as well as nozzle designs, have been highlighted in both historical and the more recent laser cladding literature. Finally, a comprehensive analysis of fluid dynamic simulations of the powder particles and their interaction with the nozzle design is provided.

This experimental study aims to extend the know-how on biomechanical performances of duplex stainless steel (DSS) for tissue engineering applications to a graded lattice geometry scaffold based on the F53 DSS (UNS S32750 according to ASTM A182) produced by laser powder bed fusion (LPBF). The same dense-out graded geometry based on rhombic dodecahedral elementary unit cells investigated in previous work on 316L stainless steel (SS) was adopted here for the manufacturing of the F53 DSS scaffold (SF53). Microstructural characterization and mechanical and biological tests were carried out on the SF53 scaffold, using the in vitro behavior of the 316L stainless steel scaffold (S316L) as a control. Results show that microstructure developed as a consequence of different volume energy density (VED) values is mainly responsible for the different mechanical behaviors of SF53 and S316L, both fabricated using the same LPBF manufacturing system. Specifically, the ultimate compressive strength (σUC) and elastic moduli (E) of SF53 are three times and seven times higher than S316L, respectively. Moreover, preliminary biological tests evidenced better cell viability in SF53 than in S316L already after seven days of culture, suggesting SF53 with dense-out graded geometry as a viable alternative to 316L SS for bone tissue engineering applications.