In this work, an artificial neural network model is established to understand the relationship among the tensile properties of as-printed Ti6Al4V parts, annealing parameters, and the tensile properties of annealed Ti6Al4V parts. The database was established by collecting published reports on the annealing treatment of selective laser melting (SLM) Ti6Al4V, from 2006 to 2020. Using the established model, it is possible to prescribe annealing parameters and predict properties after annealing for SLM Ti-6Al-4V parts with high confidence. The model shows high accuracy in the prediction of yield strength (YS) and ultimate tensile strength (UTS). It is found that the YS and UTS are sensitive to the annealing parameters, including temperature and holding time. The YS and UTS are also sensitive to initial YS and UTS of as-printed parts. The model suggests that an annealing process of the holding time of fewer than 4 h and the holding temperature lower than 850°C is desirable for as-printed Ti6Al4V parts to reach the YS required by the ASTM standard. By studying the collected data of microstructure and tensile properties of annealed Ti6Al4V, a new Hall-Petch relationship is proposed to correlate grain size and YS for annealed SLM Ti6Al4V parts in this work. The prediction of strain to failure shows lower accuracy compared with the predictions of YS and UTS due to the large scattering of the experimental data collected from the published reports.

The Ti–35Nb–7Zr–5Ta (TNZT) alloy is a promising alloy because of its biocompatibility, high specific strength, and low Young's modulus. This work aimed at investigating the viability to process the TNZT alloy by selective laser melting (SLM) and at optimizing the processing parameters to obtain densified bulk samples. The single-track approach was first used, and the optimized laser parameters were determined to produce bulk samples with a relative density of 99.0% when an energy input of 58.3 J/mm3 was used. The effect of porosity on mechanical properties was studied, and the as-built SLM samples presented slightly lower compressive strength than samples produced by Cu-mould suction casting, as a result of a columnar grain structure in the SLMed samples. Prototypes were manufactured, proving the feasibility of manufacturing parts of the TNZT alloy with complex geometry by SLM.

In this report, bulk graphene–reinforced titanium (Ti–Gr) nanocomposite with millimeter thickness was fabricated by selective laser melting process. Demonstrated by the characterizations of scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra, graphene nanoplatelets were successfully embedded into the titanium matrix with a uniform dispersion due to a fast heating–cooling process. High-resolution transmission electron microscopy was used to investigate the interface between titanium and graphene, where a certain amount of carbide was formed attribute to the chemical reaction between them during multilayer laser melting. A high density of dislocations was observed surrounding the graphene nanoplatelets in titanium matrix. The strength and elastic modulus of the nanocomposites were significantly improved, which has been demonstrated by nano-indentation tests. The hardness of the bulk Ti–Gr nanocomposites was approximately 1.27 times higher than pristine Ti counterpart. The strengthening mechanisms were discussed in detail.

Process parameters (laser power and scanning speed) for H13 steel specimens produced by selective laser melting (SLM) are optimized, and microstructural characteristics and mechanical properties are investigated. The optimum process parameters are a laser power of 170 W and a scanning speed of 400 mm/s according to the maximum relative density of 99.2%. The microstructure consists of cellular grains and columnar crystal, which are composed of lath martensite and retained austenite, and there are no carbides or other second-phase particles present. The size of cellular grains is 1 μm. Compared with the common processed (forged and heat-treated) H13, SLM H13 has similar microhardness (561 HV) and tensile strength (1909 MPa) values. However, the elongation (12.4%) is a factor of ∼3 times higher and the impact energy (14.4 J) of the SLM specimen is somewhat lower. The relationship between the microstructure and mechanical properties is discussed. Fine grains and no second-phase precipitation determine the strength and plasticity of SLM samples.

GH3536 alloy is one of the high-temperature nickel-based alloys and widely applied in aviation and aerospace industries. In this study, a combination of experiment and simulation is proposed to study the effect of processing parameters on the selective laser melting (SLM) of GH3536 powder. It is concluded that the relationship between density and laser input energy during SLM complies with a quadratic function and presents an inverted U-shaped distribution. By fitting density and input power to a quadratic polynomial, the optimal laser input energy during SLM of GH3536 alloy can be obtained. The result shows that using 275 W laser power and 960 mm/s scanning speed, the SLM GH3536 specimens can reach the maximum density. This experimental result is consistent with the simulation result obtained by analyzing molten pool dimension. Furthermore, a full process energy prediction diagram for SLM GH3536 alloy based on the simulated molten pool depth and width is proposed. The result shows that it provides an innovative and efficient method for the selection of processing parameters during SLM of GH3536 powder.

This paper illustrates the different possibilities given by additive manufacturing technologies for the creation of passive microwave hardware. The paper more specifically highlights a prototyping scheme where the 3D-printed plastic parts can be used as initial proofs of concept before considering more advanced 3D-printed parts (metal parts, for instance). First, a characterization campaign has been made on common plastics used by a 3D printer using the fused deposition modeling and material jetting (Polyjet©) technologies. The impact of the manufacturing strategy (high-speed or high-accuracy) on the part roughness, as well as on the dielectric material permittivity and loss tangent, has been specifically studied at 10 and 16 GHz. Based on a specifically optimized and deeply explained characterization method, the conductivity of a coating based on silver paint has also been characterized on such plastic parts at 10 and 40 GHz. These plastic materials and coating have been used for the creation of quasi-elliptic and tuning-free bandpass filters centered at 6 and 12 GHz and compared with a similar filter made of stainless steel by selective laser melting. Finally, a compact rectangular TE10 to circular TE01 mode converter also undergoes one prototyping step out of plastic before moving to an advanced part made out of stainless steel. This mode converter, which is made in a single part, is designed to operate from 28 to 36 GHz as a tuning-free final demonstrator.

Selective laser melting (SLM) technology efficiently solves the current manufacturing challenges of high-performance porous structure components, due to its freeform fabrication principle. As the most basic and crucial structure element, the nodes of porous structure component play an important role in its mechanical property. In this study, finite element method was used to investigate the thermal behavior during SLM processing of micro-scale node-structure. The dynamic size of molten pool was continuously predicted and consequently the typical “necking” effect was found, which was consistent with the experiment results. Besides, the influence of laser scan speed on temperature and temperature gradient of molten pool was also analyzed. The results indicated that the “necking” effect became more conspicuous with the applied scan speed increasing, which significantly deteriorated the mechanical property of porous structure components.

A systematic analysis of effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabricated by selective laser melting was conducted. By composition optimization of alloying elements, the desirable martensitic structure was directly obtained based on high-speed laser induction and the content of retained austenite was observed to be different under various laser parameters. Using an optimized scan speed of 1600 mm/s could lead to the highest densification level of 99.24% and the lowest content of retained austenite of 3.5%, hence acquiring a considerably high Rockwell hardness of 61.9 HRC, a reduced coefficient of friction of 0.40, and wear rate of 1.8 × 10−5 mm3/N m. A thorough investigation of dimension offset due to martensite transformation in conjunction with theoretical calculation was performed. Lower top surface roughness (5.25 μm) and reduced side roughness (13.84 μm) were achieved at the optimized scan speed of 1600 mm/s.

Incineration or disposal of carbon fiber waste from the aircraft industry leads to serious energy consumption and environmental pollution. The use of this waste as reinforcement is a wise approach to appreciate the high performance of the carbon fiber. In this study, the sliding wear and frictional behavior of recycled carbon fiber prepreg (rCFP) reinforced polypropylene (PP) prepared via melt compounding method using an internal mixer were studied. The samples were categorized into PP reinforced by carbon fiber with resin (A) and carbon fiber without resin (B). Pin-on-disc method was utilized to evaluate the effect of rCFP content and physical condition of fibers on tribological performance of the composites. The results were supported by morphological analyses using scanning electron microscopy. It was found that polymer composites B for rCFP without resin exhibited better tribological performance than composites category-A. The addition of rCFP into PP was observed to increase its wear resistance with minimum coefficient of friction achieved at 3 wt% of rCFP content for both polymer composites.

Al–12Si (80 vol%)–Ti52.4Al42.2Nb4.4Mo0.9B0.06 (at.%) (TNM) composites were successfully produced by the selective laser melting (SLM). Detailed structural and microstructural analysis shows the formation of the Al6MoTi intermetallic phase due to the reaction of the TNM reinforcement with the Al–12Si matrix during SLM. Compression tests reveal that the composites exhibit significantly improved properties (∼140 and ∼160 MPa higher yield and ultimate compressive strengths, respectively) compared with the Al–12Si matrix. However, the samples break at ∼6% total strain under compression, thus showing a reduced plasticity of the composites. Sliding wear tests were carried out for both the Al–12Si matrix and the Al–12Si–TNM composites. The composites perform better under sliding wear conditions and the wear rate increases with increasing loads. At high loads, the wear takes place at three different rates and the wear rate decreases with increasing experiment duration.

In this study, Aluminum-based nanocomposites with hybrid reinforcements were successfully prepared by mechanical alloying, followed by consolidation using selective laser melting (SLM). The evolution of particle morphology and microstructural features of the milled powders at various milling times was studied. The results indicated that the milled powder particles experienced a coarsening stage at the early 5 h milling and followed by a continuous refinement during 5–20 h milling. After 20 h of milling, the original coarse needle-like Al3.21Si0.47 evolved into nanometer/submicrometer-sized spherical Al3.21Si0.47. Meanwhile, both fine Al3.21Si0.47 and ex-situ nanoscale TiN particles distributed uniformly within the Al matrix. By SLM processing of the 20-h powder, a near fully dense part with a uniform microstructure consisting of circularly dispersed and submicrometer-sized reinforcement particles embedded in α-Al matrix was obtained. The Vickers hardness and coefficient of friction of the SLM-processed part reached 178 HV0.1 and 0.38, respectively.

The effect of annealing on the tribological and corrosion properties of Al–12Si samples produced by selective laser melting (SLM) is evaluated via sliding and fretting wear tests and weight loss experiments and compared to the corresponding material processed by conventional casting. Sliding wear shows that the as-prepared SLM material has the least wear rate compared to the cast and heat-treated SLM samples with abrasive wear as the major wear mechanism along with oxidation. Similar trend has also been observed for the fretting wear experiments, where the as-prepared SLM sample displays the minimum wear loss. On the other hand, the acidic corrosion behavior of the as-prepared SLM material as well as of the cast samples is similar and the corrosion rate is accelerated by increasing the heat treatment temperature. This behavior is due to the microstructural changes induced by the heat treatment, where the continuous network of Si characterizing the as-prepared SLM sample transforms to isolated Si particles in the heat-treated SLM specimens. This shows that both the wear and corrosion behaviors are strongly associated with the change in microstructure of the SLM samples due to the heat-treatment process, where the size of the hard Si particles increases, and their density decreases with increasing annealing temperature.