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Material extrusion additive manufacturing of metal (metal MEX), which is one of the 3D printing processes, has gained more interests because of its simplicity and economics. Metal MEX process is similar to the conventional metal injection moulding (MIM) process, consisting of feedstock preparation of metal powder and polymer binders, layer-by-layer 3D printing (metal MEX) or injection (MIM) to create green parts, debinding to remove the binders and sintering to create the consolidated metallic parts. Due to the recent rapid development of metal MEX, it is important to review current research work on this topic to further understand the critical process parameters and the related physical and mechanical properties of metal MEX parts relevant to further studies and real applications. In this review, the available literature is systematically summarised and concluded in terms of feedstock, printing, debinding and sintering. The processing-related physical and mechanical properties, i.e., solid loading vs. dimensional shrinkage maps, sintering temperature vs. relative sintered density maps, stress vs. elongation maps for the three main alloys (316L stainless steel, 17-4PH stainless steel and Ti-6Al-4V), are also discussed and compared with well-established MIM properties and MIM international standards to assess the current stage of metal MEX development.

The spark plasma sintering (SPS) method is of great interest to the powder and powder metallurgy industry and material researchers of academia for both product manufacturing and advanced material research and development. Today in Japan, a number of SPS products for different industries have already been realized. Today’s fifth-generation SPS systems are capable of producing parts of increasing size, offering improved functionality, reproducibility, productivity, and cost. For instance, pure nano-Tungsten Carbide WC powder (no additives) is fully densified with a nano-grain-sized structure for glass lens application in the optics industry. The SPS is now moving from scientific academia and/or R&D proto-type materials level usage to practical industry use product stage utilizing in the field of electronics, automotive, mold and die, cutting tools, fine ceramics, clean energy, biomaterials industries, and others. This paper reviews and introduces the peculiar phenomenon of SPS and the progress of SPS technology, method, development of SPS systems, and its industrial product applications.

Binder jet additive manufacturing enables the production of complex components for numerous applications. Binder jetting is the only powder bed additive manufacturing process that is not fusion-based, thus manufactured parts have no residual stresses as opposed to laser-based additive manufacturing processes. Binder jet technology can be adopted for the production of various small and large metallic parts for specific applications, including in the biomedical and energy sectors, at a lower cost and shorter lead time. One of the most well-known types of stainless steels for various industries is 316L, which has been extensively manufactured using binder jet technology. Binder jet manufactured 316L parts have obtained near full density and, in some cases, similar mechanical properties compared to conventionally manufactured parts. This article introduces methods, principles, and applications of binder jetting of SS 316L. Details of binder jetting processes, including powder characteristics (shape and size), binder properties (binder chemistry and droplet formation mechanism), printing process parameters (such as layer thickness, binder saturation, drying time), and post-processing sintering mechanism and densification processes, are carefully reviewed. Furthermore, critical factors in the selection of feedstock, printing parameters, sintering temperature, time, atmosphere, and heating rate of 316L binder jet manufactured parts are highlighted and summarized. Finally, the above-mentioned processing parameters are correlated with final density and mechanical properties of 316L components to establish a guideline on feedstock selection and process parameters optimization to achieve desired density, structure and properties for various applications.

This paper aims to provide a theoretical and experimental understanding of the importance of novel 2D materials in solid-film lubrication, along with modulating strategies adopted so far to improve their performance for spacecraft and industrial applications. The mechanisms and the underlying physics of 2D materials are reviewed with experimental results. This paper covers some of the widely investigated solid lubricants such as MoS2, graphene, and boron compounds, namely h-BN and boric acid. Solid lubricants such as black phosphorus that have gained research prominence are also discussed regarding their application as additives in polymeric materials. The effects of process conditions, film deposition parameters, and dopants concentration on friction and wear rate are discussed with a qualitative and quantitative emphasis that are supported with adequate examples and application areas and summarized in the form of graphs and tables for easy readability. The use of advanced manufacturing methods such as powder metallurgy and sintering to produce solid lubricants of superior tribological performance and the subsequent economic gain from their development as a substitute for liquid lubricant are also evaluated.

This article uses powder pressing and sintering methods to prepare iron-based friction materials. The influence of molybdenum on the microstructure and comprehensive properties of powder metallurgy friction materials was studied from the aspects of density, hardness, and wear resistance. The results show that with the increase of Mo mass fraction, the sintering density of iron-based friction materials gradually increases, and the hardness of sintered materials first shows an increasing trend. As the Mo content increases by more than 12%, the hardness of sintered friction materials decreases. With the addition of Mo, the wear amount of the friction material first decreases and then increases. When the mass fraction of Mo added to the sintered friction material is 12%, the wear rate of the material is lower than that of other samples, and it has good wear resistance. Adding Mo element to iron copper based friction materials improves the wear resistance of sintered friction materials due to the strengthening effect of Mo.

Residual stress profiles were mapped using neutron diffraction in two simple prism builds of Inconel 718: one fabricated with electron beam melting (EBM) and the other with direct laser metal sintering. Spatially indexed stress-free cubes were obtained by electrical discharge machining (EDM) equivalent prisms of similar shape. The (311) interplanar spacings from the EDM sectioned sample were compared to the interplanar spacings calculated to fulfill stress and moment balance. We have shown that applying stress and moment balance is a necessary supplement to the measurements for the stress-free cubes with respect to accurate stress calculations in additively manufactured components. In addition, our work has shown that residual stresses in electron beam melted parts are much smaller than that of direct laser metal sintered parts most likely due to the powder preheating step in the EBM process.

High-entropy alloys (HEAs) prefer to form single-phase solid solutions (body-centered cubic (BCC), face-centered cubic (FCC), or hexagonal closed-packed (HCP)) due to their high mixing entropy. In this paper, we systematically review the mechanical behaviors and properties (such as oxidation and corrosion) of BCC-structured HEAs. The mechanical properties at room temperature and high temperatures of samples prepared by different processes (including vacuum arc-melting, powder sintering and additive manufacturing) are compared, and the effect of alloying on the mechanical properties is analyzed. In addition, the effects of HEA preparation and compositional regulation on corrosion resistance, and the application of high-throughput techniques in the field of HEAs, are discussed. To conclude, alloy development for BCC-structured HEAs is summarized.

The conventional forging process faces challenges in manufacturing complex aerospace components using 7075 aluminum alloy. This study investigates the effects of sintering temperatures on the properties of 7075 aluminum alloy preforms and optimizes multi-directional forging parameters through finite element simulations and experimental validation. The optimized powder forging parameters include a sintering temperature of 580°C (heating rate: 50 °C/min, pressure: 40 MPa, holding time: 4 h) and forging conditions of 420 °C with a punch speed of 8 mm/s. Post-T73 heat treatment significantly enhanced the density (99.87%), hardness (150 HB), and tensile strength (582.3 MPa) of powder-forged joints, outperforming conventional bar-forged counterparts under identical conditions.

In this paper, the effects of copper infiltrant amount and copper infiltration method on the mechanical properties of Fe-Cu-C-based sintered steel were investigated. The results indicate that the density, tensile strength, impact energy, and hardness of the sintered steel increase with higher copper infiltration. The optimal mechanical properties were achieved when the copper infiltrant amount reached 15%, resulting in a surface hardness of HRC31, an impact energy of 31.34 J, and an ultimate tensile strength of 759 MPa. Furthermore, different copper infiltration methods affected the material’s mechanical properties. When the copper infiltrant amount was 12.5%, the impact energy of the sintered steel sample was 15.41% higher using the bottom copper infiltration process (30.19 J) compared to the top copper infiltration process (26.16 J). These findings provide valuable insights for enhancing the mechanical properties of iron-based powder metallurgy sintered steel with copper infiltration.

Alloys with superior properties represent the main topic of recent studies due to their effectiveness in reducing the cost of equipment maintenance and enhancing usage time, in addition to other benefits in domains such as geothermal, marine, and airspace. Al0.5CrFeNiTi was produced by solid state processing in a planetary ball mill, with the objective of obtaining a high alloying degree and a homogenous composition that could be further processed by pressing and sintering. The metallic powder was technologically characterized, indicating a particle size reduction following mechanical alloying processing when compared to the elemental raw powder materials. The microstructural analysis presented the evolution of the alloying degree during milling but also a compact structure with no major defects in the pressed and sintered bulk samples. The X-ray diffraction results confirmed the presence of face-centered cubic (FCC) and body-centered cubic (BCC) phases, predicted by the theoretical calculations, along with a hexagonal close-packed (HCP) phase, where the Al, Cr, Fe, Ni, and Ti phase was identified in both the alloyed powder material and sintered sample.