The exploitation of mechanical properties and customization possibilities of 3D printed metal parts usually come at the cost of complex and expensive equipment. To address this issue, hybrid metal/polymer composite filaments have been studied allowing the printing of metal parts by using the standard Fused Filament Fabrication (FFF) approach. The resulting hybrid metal/polymer part, the so called “green”, can then be transformed into a dense metal part using debinding and sintering cycles. In this work, we investigated the manufacturing and characterization of green and sintered parts obtained by FFF of two commercial hybrid metal/polymer filaments, i.e., the Ultrafuse 316L by BASF and the 17-4 PH by Markforged. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDS) analyses of the mesostructure highlighted incomplete raster bonding and voids like those observed in conventional FFF-printed polymeric structures despite the sintering cycle. A significant role in the tensile properties was played by the building orientation, with samples printed flatwise featuring the highest mechanical properties, though lower than those achievable with standard metal additive manufacturing techniques.

Hybrid Metal/Polymer Filaments for Fused Filament Fabrication (FFF) to Print Metal Parts

Nowadays, additive manufacturing (AM) technologies have been widely used in construction, medical, military, aerospace, fashion, etc. The advantages of AM (e.g., more design freedom, no restriction on the complexity of parts, and rapid prototyping) have attracted a growing number of researchers. Increasing number of papers are published each year. Until now, thousands of review papers have already been published in the field of AM. It is, therefore, perhaps timely to perform a survey on AM review papers so as to provide an overview and guidance for readers to choose their interested reviews on some specific topics. This survey gives detailed analysis on these reviews, divides these reviews into different groups based on the AM techniques and materials used, highlights some important reviews in this area, and provides some discussions and insights.

A survey of additive manufacturing reviews

Investigation of size effect on band structure of 2D nano-scale phononic crystal based on nonlocal strain gradient theory

316L steel is predominantly used in manufacturing the components of high-pressure boilers, heat exchangers, aerospace engines, oil and gas refineries, etc. Its notable percentage of chromium offers resistance against corrosion and is mostly implemented in harsh environments. However, long-term exposure to these components in such environments can reduce their corrosion resistance property. Particularly at high temperatures, the oxide film formed on this type of steel reacts with the chloride, sulfides, sulfates, fluorides and forms intermetallic compounds which affect its resistance, followed by failures and losses. This work is focused on investigating the hardness, microstructure and corrosion resistance of the laser cladded Colmonoy-6 particles on the 316L steel substrate. The cladded specimens were dissected into cubic shapes and the microstructure present in the cladded region was effectively analyzed using the FESEM along with the corresponding EDS mapping. For evaluating the hardness of the cladded samples, the nanoindentation technique was performed using the TI980 TriboIndenter and the values were measured. The potentiodynamic polarization curves were plotted for both the substrate and clad samples at 0, 18, 42 and 70 h for revealing the corrosion resistance behavior. In addition, the EIS analysis was carried out to further confirm the resistance offered by the samples. The surface roughness morphology was evaluated after the corrosion process using the laser microscope, and the roughness values were measured and compared with the substrate samples. The result showed that the cladded samples experience greater hardness, lower values of surface roughness and provide better corrosion resistance when compared with substrate samples. This is due to the deposition of precipitates of chromium-rich carbide and borides that enhances the above properties and forms a stable passive film that resists corrosion during the corrosion process.

Investigation on Microstructure, Nanohardness and Corrosion Response of Laser Cladded Colmonoy-6 Particles on 316L Steel Substrate

The number of additive manufacturing methods and materials is growing rapidly, leaving gaps in the knowledge of specific material properties. A relatively recent addition is the metal-filled filament to be printed similarly to the fused filament fabrication (FFF) technology used for plastic materials, but with additional debinding and sintering steps. While tensile, bending, and shear properties of metals manufactured this way have been studied thoroughly, their fatigue properties remain unexplored. Thus, the paper aims to determine the tensile, fatigue, and impact strengths of Markforged 17-4 PH and BASF Ultrafuse 316L stainless steel to answer whether the metal FFF can be used for structural parts safely with the current state of technology. They are compared to two 316L variants manufactured via selective laser melting (SLM) and literature results. For extrusion-based additive manufacturing methods, a significant decrease in tensile and fatigue strength is observed compared to specimens manufactured via SLM. Defects created during the extrusion and by the pathing scheme, causing a rough surface and internal voids to act as local stress risers, handle the strength decrease. The findings cast doubt on whether the metal FFF technique can be safely used for structural components; therefore, further developments are needed to reduce internal material defects.

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Strength Properties of 316L and 17-4 PH Stainless Steel Produced with Additive Manufacturing

Mechanical and thermal properties of stainless steel parts, manufactured by various technologies, in relation to their microstructure

Selective laser melting (SLM) is used to fabricate nearly fully dense 316L stainless steel (SS) samples in this study. A variety of advanced characterization techniques were conducted to identify dominant phases, important crystallographic features, microstructural features, and elemental composition. Porosity of the sample was found to be 0.02% which is the lowest porosity content reported for SLM-processed 316L SS. Microstructural analysis exhibits some columnar grains with epitaxial growth representing complete adhesion between the layers. Existence of some fine cellular grains inside the melt pools is an indication of rapid solidification during the printing process. The strength of this study lies in the addition of new crystallographic information such as lattice parameters of SLM-processed 316L. Finally, using information obtained from the literature, it was possible to better understand the effect of chosen process parameters to achieve nearly fully dense material in the present study.

Microstructure Analysis of High-Density 316L Stainless Steel Manufactured by Selective Laser Melting Process

Among various additive manufacturing methods, selective laser melting (SLM) is a practical method for metal manufacturing due to its ability to make complex geometry and fabricate parts with superior mechanical properties. Utilization of high strength laser in SLM system forms a high temperature gradient which may alter microstructure of 3D printed metals due to rapid cooling during solidification process. The present study focuses on the microstructural evolution of AISI 316L stainless steel manufactured by SLM to better understand its characteristics and features for further improvement of this technology. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and TEM with energy dispersive X-ray spectroscopy (EDX) have been carried out on 3D printed samples. The microstructural observation indicated very low porosity with homogeneous composition throughout the specimen. A layer by layer structure with columnar grains grown in the direction of heat transfer was clearly seen in the microstructure. A dense dislocation network with a single austenite phase crystallographic structure was identified as well from nanoscale observation of the samples.

Ismat Ara

Papers

Mechanical and thermal properties of stainless steel parts, manufactured by various technologies, in relation to their microstructure

Microstructure Analysis of High-Density 316L Stainless Steel Manufactured by Selective Laser Melting Process

Microstructural Characteristics of Stainless Steel 316L Processed by Selective Laser Melting Technology