Wire arc additive manufacturing (WAAM) is an additive technology in which a metal wire is melted with an electric arc, and the parts are formed layer by layer. Austenitic stainless steel wires are promising materials in the manufacture of parts via WAAM. Austenitic steels have good ductility and corrosion resistance, but low strength. Nitrogen alloying, which leads to solid-solution hardening, can increase strength. In addition, austenitic stainless steels are sensitive to the formation of hot cracks during welding, which can be corrected by the low content of δ-ferrite in the structure of such steels.

In this work, a flux-cored wire was developed using WAAM, which ensures the formation of an austenitic–ferritic structure of the deposited metal. The chemical composition of the deposited metal was as follows: wt. %: 0.055 C; 0.43 Si; 5.0 Mn; 20.1 Cr; 4.1 Ni; 2.1 Mo; 2.9 Cu; 0.319 N.

The characteristics of the WAAM product made from developed flux-cored wire were compared with the properties of AISI 321 steel. The deposited layers of the experimental composition were characterized by greater microhardness and improved strength characteristics, with a slight decrease in plastic properties, compared with AISI 321 steel. In addition, the developed material surpasses AISI 321 steel in terms of the pitting potential in artificial seawater. The phase composition of the deposited layers is deformationally stable: no austenite–martensite phase transformation was detected in tensile plastic deformation tests.

This research was carried out with the support of a grant from the Russian Science Foundation (RSF) No. 24-19-20059 (https://rscf.ru/en/project/24-19-20059/) and the Government of the Sverdlovsk Region.

Owing to their cost-effective and comprehensive physical and chemical properties, steels are often utilized as structural materials in the construction of bridges, industrial equipment, marine vessels, and offshore platforms. Most of these steels are central components of load-bearing applications, which are usually exposed to harsh corrosion environments such as marine atmosphere, acid fog, and polluted industrial corrosive effluents. Conventional methods rely on coatings such as painting, electroplating, or galvanizing, which involve operational complexities, high costs, and environmental concerns. A potential solution to these disadvantages involves improving their inherent corrosion resistance through the refinement of the grain structure of alloy steels. In this study, the possibility of graphite solution as a quenchant for steel is explored. Since graphite has an excellent thermal conductivity of 2000 W/m K compared to water's conductivity of 0.598 W/m K, its quenching characteristics show promising results. In this study, the corrosion resistance of the steel samples was evaluated under both stagnant and flow-accelerated conditions. The graphite-quenched samples consistently demonstrated superior corrosion resistance compared to the water-quenched ones, particularly in a flow-accelerated environment. Microstructural analysis supported these findings, showing reduced surface degradation in graphite-quenched specimens. The Tafel plot analysis further confirmed the results, with the lower corrosion current density of graphite-quenched samples being shown in both stagnant and flow-accelerated conditions. Moreover, the graphite-quenched samples had a more positive corrosion potential, which indicates their greater electrochemical stability. This research highlights the potential of graphite-based quenchants as viable alternatives for applications that require enhanced corrosion resistance, without significantly compromising hardness.

Industry 4.0, the fourth industrial revolution, is focused on the complete digitalisation of manufacturing, and has been spearheaded by the development of direct digital manufacturing technologies, such as selective laser melting and extruder-based 3D printing. As a consequence, there is the possibility Tthat significant changes will be made to the way in which products are designed and fabricated. In particular, these approaches can take advantage of digital optimisation processes such as topology optimisation. As an example, the form of a particular product can be optimised against a specific property, such as mass, as additive manufacturing allows materials to be placed at any point in the volume. We can easily envisage that the target function in the optimisation could involve other properties such as carbon footprint and the possibility of recycling or composting. These powerful optimisation processes are unlocked within the context of digital manufacturing if the complete chain is digital. As a result, in the design and fabrication cycle, the material selected for that product will naturally play a critical role in determining the properties of the final product. Some additive manufacturing technologies are able to fabricate in a straightforward and controlled manner, with spatial variations in properties. Taking advantage of these developments would provide additional advantages to digital fabrication technologies. This work is focused on developing a framework for handling materials within digital manufacturing processes to enable advances in a digital manner as described above. It is particularly challenging to identify a single framework which is suitable for all types of materials, including metals, ceramics, glass and polymers, although to do so would be especially advantageous with respect to the optimisation of products with regard to sustainability. This work proposes that the coordinate space of materials only makes sense if it is related to what is available in the specific manufacturing process.

Abstract

Metastable β-titanium alloys are attractive for the aerospace industry and medical applications, due to their low density, high strength, low young modulus, and excellent hardenability. Among these alloys, Titanium Grade 21S is renowned for its outstanding elevated temperature strength, creep resistance, corrosion resistance and mechanical properties. However, its limited weldability and poor thermal conductivity present significant challenges to traditional manufacturing methods, resulting in increased difficulty and costs. This study explores the potential of laser powder directed energy deposition (LP-DED) to fabricate Ti-21S samples. This additive manufacturing (AM) technique as compared to other fusion-based AM processes, offers faster material deposition rates, resulting in faster build times. The produced components were comprehensively evaluated for their microstructure, mechanical properties, and corrosion behavior using various methodologies. Based on the defect analysis, it was achieving >99.9% of theoretical density with appropriate processing parameters. Microstructure analysis indicated a fully beta-phase microstructure alongside notable mechanical strength and corrosion resistance. Hardness and microstructural uniformity were consistent across all samples, while electrochemical tests demonstrated robust resistance to aggressive environments. These findings underscore the effectiveness of LP-DED as a processing technique for Ti-21S, preserving its advantageous properties and addressing the limitations of conventional manufacturing.

Keyword: Beta-Ti21S alloy; Laser powder directed energy deposition; Additive manufacturing; electrochemical; Ti alloys.

Laser Powder Bed Fusion (LPBF), a type of additive manufacturing (AM), allows for the production of metallic lattice structures with highly adaptable geometries and graded material properties. Functionally Graded Lattice Structures (FGLSs) are advantageous for high-performance applications, including biomedical implants. These advanced structures, produced through additive manufacturing, exhibit spatially varying mechanical properties that are crucial for mimicking biological gradients, thereby reducing stress shielding and promoting better integration.

This research explores the design, fabrication, and mechanical characterization of FGLS using AlSi10Mg. Three advanced lattice topologies were investigated: Gyroid, Split-P (a TPMS-derived surface), and Stochastic Voronoi (ST). Tensile and compression specimens were fabricated via LPBF, with functional gradation introduced by varying strut and wall thickness along the specimen length. The mechanical properties, including elastic modulus, ultimate tensile and compressive strength, and energy absorption, were evaluated through quasi-static tensile and compression tests. High-resolution computed tomography (CT) scans were used to capture the as-built geometry, verify dimensional accuracy, and identify potential manufacturing defects. These images were further analyzed to assess internal fidelity, strut thickness deviations, and porosity, supporting the mechanical testing with geometric validation. Moreover, scanning electron microscopy (SEM) analysis was carried out on the fracture surfaces of the broken specimens to better understand the behaviour of the material.

Considering compressive properties, in every case, at any density, cylindrical cell maps outperform cubic ones. In compression samples, switching from cylindrical to cubic in Split-P cuts energy absorption by only 10%, but in Gyroid it drops 24%. Considering tensile specimens, in ST and Split-P lattices, stiffness scales nearly one to one with relative volume. However, in gyroid lattices, lowering the thickest walls stiffens the structure while thinning the smallest walls softens it. AM defects resulting in sudden fracture under localized high stress and brittle behaviour, even in ductile alloys like AlSi10Mg.

Ceramics based on zirconium carbonitride belongs to the class of Ultra-High Temperature Ceramics and has a set of promising properties, such as high hardness and strength, resistance to aggressive chemicals, high melting temperatures and oxidative resistance. Due to the complication of the structure when creating ZrCN-ZrO₂ ceramics, it becomes possible to qualitatively improve the properties of the material, namely to take a significant step in solving the key problem found in materials of this class: their low crack resistance. In the course of this work, ceramic samples of ZrCN-ZrO₂ were obtained with various stoichiometry by hot pressing and spark plasma sintering. It was established that during hot pressing, reduced porosity in the samples is achieved, within 2%. It is observed that with an increase in the ZrO₂ content, a decrease in the porosity of materials is achieved. For consolidated samples, it was found that when the carbonitride is formed, the hardness of the materials increased to values of 18 GPa with an increase in the ratio of N/(C+N) in the studied materials and a decrease in porosity. A similar situation is observed for Young’s modulus, showing an increase of up to 427 GPa. When examining the crack resistance of ZrCN-ZrO₂ ceramics, it was found that with an increase in the ZrO₂ content, the crack resistance of materials increases to the values of 4.3 MPa·m^1/2. When studying oxidative behavior, it was found that the samples underwent active oxidation from a temperature of 800 ℃. With an increase in the ZrO₂ content in the material under study, an increase in the oxidative resistance of the samples was observed as a result of the peroxidation process of cubic zirconium dioxide. Due to the complicated structure of ceramics based on zirconium carbonitride, the mechanical properties increased along with the oxidative resistance of the materials.

Arsenate(V) ions occur naturally in the environment as a component of the lithosphere and, due to their relatively easy penetration into groundwater, also in the hydrosphere. However, in recent decades, their content has increased significantly due to intensive human activity, primarily related to the development of the mining and metallurgical industries. Arsenic compounds are characterized by high toxicity and proven carcinogenic properties. Therefore, it is necessary to search for increasingly effective methods for their removal from the natural environment. The most popular method is sorption. The aim of the presented research was to remove HAsO42- anions from aqueous solutions using layered double hydroxides (LDHs) as adsorbents. Their structure consists of positively charged layers of mixed hydroxides of metal cations, in this case Cu²⁺, Mg²⁺, Zn²⁺, and Al³⁺, arranged alternately with charge-compensating interlayers of Cl⁻ or CO₃²⁻ anions. LDH, both before and after the sorption process, was analyzed using the following analytical techniques: (i) thermal analysis using thermogravimetry (TG) and differential scanning calorimetry (DSC) methods (SETSYS16/18 analyzer, Setaram); (ii) Fourier transform infrared spectroscopy (FTIR) (Alpha spectrometer, Bruker Inc., Germany); and (iii) powder X-ray diffraction (XRD) (MiniFlex II diffractometer, Rigaku). The concentration of HAsO₄^2- ions in the solutions was determined by a colorimetric method based on ammonium molybdate using a JASCO V-660 UV-Vis spectrophotometer. The effect of contact time, initial concentration and pH of the solutions on the sorption efficiency of As(V) ions on LDH materials was determined. Layered double hydroxides, particularly in the chloride form, have proven effective in removing arsenic contaminants from aqueous systems. Depending on the LDH form, different mechanisms of As ion sorption were observed: surface adsorption or mixed adsorption, with a significant contribution from ion exchange.

This research is funded by the Lithuanian Research Council under the postdoctoral fellowship project no. S-PD-24-145.

Electrohydrodynamic (EHD) jet printing is a new micro-additive manufacturing technology that uses electric fields to precisely deposit material through a nozzle, achieving high resolutions with high-viscosity inks. Seeing as it is a recent technology, bio-based inks have yet to be designed and optimized. Hydroxypropyl methylcellulose (HPMC) stands out as a biodegradable biopolymer with excellent compatibility, paving the way for sustainable smart packaging sensors.

In this work, solutions with different concentrations of HPMC (1%, 2% and 3%) in ethanol (from 0% to 90%) were evaluated and characterized in terms of viscosity, surface tension and conductivity, and used in printability tests using a home-made EHD jet printer. Certain parameters of the EHD jet printer were fixed, such as the flow rate (28.28 μl h^-1, corresponding to a shear rate of 10 s^-1 in the nozzle type), working distance (1 mm), substrate (glass with a 100 nm layer of tungsten and titanium) and the nozzle diameter and material (200 μm, stainless steel). The speed was varied between 1 mm s^-1 and 15 mm s ^-1 and the voltage was manipulated between 1.5 kV and 2.5 kV until Taylor’s Cone formation.

Then, a printability ternary graph (water–ethanol–HPMC) was obtained, selecting HPMC- based bioinks that achieved higher resolutions (dots and lines as small as 50 μm, determined by microscopy), with less clogging and reproducible results. The printable zone was obtained from concentrations between 1 and 2% HPMC in 10%-50% ethanol. In this range, the bioinks present viscosities of 13 mPa s to 100 mPa s, a surface tension of 29 mNm to 42 mNm and conductivities of 16 μS cm^-1 to 69 μS cm^-1.

Overall, the results show the potential of using HPMC to develop bioinks compatible with EHD jet printing, foreseeing their use on food and biomedical applications.

Laser Powder Bed Fusion (L-PBF) is an advanced additive manufacturing (AM) technique widely used for producing complex metal components with high precision and flexibility enables the development of new alloys and metal matrix. AISI 316L stainless steel, commonly employed in L-PBF, is known for its excellent corrosion resistance and ductility, However, its relatively low hardness and limited wear resistance present significant limitations in more demanding applications. To address these challenges, this study investigates the use of hexagonal boron nitride (BN) as a reinforcing phase to modify the microstructure and improve the mechanical properties of L-PBF AISI 316L parts. Microstructural characterization through optical microscopy (OM) and scanning electron microscopy (SEM) revealed distinct modifications in grain morphology, and the presence of solidification cracks, primarily attributed to the rapid cooling inherent to the LPBF process. X-ray diffraction (XRD) identified phase composition and secondary phases, while x-ray computed tomography (XCT) assessed internal porosity and subsurface defects in the fabricated parts. The mechanical results demonstrate that incorporating BN into L-PBF AISI 316L leads to a substantial improvement in performance. Nanoindentation hardness increased from 5.01 GPa to approximately 20%, while the microhardness rose from 210 HV by about 15%. These findings highlight that BN reinforcement is an effective strategy for enhancing the strength and durability of L-PBF AISI 316L components.

Clear aligners are a new technique in dentistry that involves moving teeth using a dental appliance made from transparent, thermoplastic material, based on standardised movements programmed by software. Conventionally, the thermoplastics in use were copolyesters and polyurethanes, but the need for more precise and comfortable treatments has pushed the industry into using combinations of thermoplastics. [1], [2]

¨This project aims to manufacture multilayers from widely available materials with comparable properties to commercial multilayers of unknown composition, and to control the thermomechanical properties to adapt multilayers to different treatment situations.

The thermomechanical properties of different thermoplastics suitable for manufacturing clear aligners were analysed by DMTA, DSC, tensile testing, and stress relaxation. Later, multilayers were manufactured using thin layers of different thermoplastics. Finally, the multilayers were analysed in the same fashion as the original thermoplastics.

The results show a high similarity in thermomechanical properties between homemade and commercial multilayer materials, and a better performance of both materials against conventional copolyesters and polyurethanes in terms of storage and loss modulus, elastic modulus, yield strain, and stress relaxation. Moreover, those properties can be controlled by selecting wisely the thermoplastics in the multilayer.

In conclusion, it is possible to manufacture clear aligners from widely available materials, but it is also feasible to adapt the properties of the thermoplastic to each treatment situation in an easy manner. Multilayer thermoplastics are hence one of the best candidates in the upcoming generation of personalised-force clear aligners.

Work supported by a grant for an industrial PhD of the Community of Madrid regional Government (IND2022/IND-23679), in collaboration with Secret Aligner S.L.

[1] N. Cenzato et al ‘Materials for Clear Aligners—A Comprehensive Exploration of Characteristics and Innovations: A Scoping Review’, Applied Sciences, vol. 14, 2024.

[2] D. Ciavarella et al., ‘Comparison of the Stress Strain Capacity between Different Clear Aligners’, TODENTJ, vol. 13,2019.