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.

This work presents the synthesis of functional fluorescent latexes and their subsequent application in producing advanced fluorescent filaments for the additive manufacturing of smart and visually responsive objects. The fluorescent latex particles were obtained through a controlled emulsion polymerization involving methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EGDMA), and acrylamide (AAm), with sodium dodecyl sulfate, sodium bicarbonate, and triton X-100 as stabilizers, and potassium persulfate as the free-radical initiator under an inert argon atmosphere. Functionalization of the latex was achieved by incorporating 2,5-bis(5-tert-butyl-2-benzoxazolyl) thiophene (BBT) at 5 wt% of the polymer solids, providing strong optical emission psropertie. FTIR spectroscopy confirmed the presence of characteristic ester and amide functionalities, while dynamic light scattering (DLS) analysis revealed a mean particle diameter of 156.9 nm with a polydispersity index (PDI) of 0.27, indicating a narrow size distribution. The BBT-latex displayed intense green fluorescence in dark environments and was directly blended with polylactic acid (PLA) without dilution to produce composite fluorescent filaments via extrusion. These filaments not only exhibited enhanced fluorescence but also demonstrated improved mechanical strength compared to pure PLA. The 3D printing tests yielded objects that appeared white under daylight yet emitted vivid green luminescence under dark conditions. This study demonstrates the potential of BBT-latex/PLA composites as multifunctional materials for fabricating 3D-printed structures that combine aesthetic, optical, and structural functionalities, opening new opportunities for smart product design.

The foundry industry, particularly the knock-out and cleaning stations for removing residual moulding sand and gating systems after casting, is among the most exposed to occupational hazards and harmful factors for workers.

The assumptions adopted in the automation project for the cleaning process of large-scale castings indicate a potential reduction in processing time by 30%, alongside a 6% total cost reduction per finished casting.

As part of the cleaning process, it is proposed to integrate 3D scanning of the actual part. Based on machine vision imaging, the scanned model is compared to its digital twin. The resulting numerical excess material, confirmed through texture-based surface imaging (identifying residual moulding compounds), defines the specific areas of the casting targeted for abrasive blasting.

The use of a dedicated robotic arm will significantly simplify the scanning operation. Once the 3D camera is returned to the tool storage station and the blasting head toolpaths are generated, the robotic arm will replace the human operator during the abrasive treatment phase. Initially, the process will be semi-automated and require operator involvement. However, after optimization using artificial intelligence algorithms and the development of a comprehensive comparison database, full integration of the processing chain scanning → 3D model → blasting head will be achieved, eliminating human decision-making from the workflow.

A final textured surface scan of the cleaned part will validate and ensure that the casting meets the required surface quality standards.

The AUTOWIND project, no. 1/Ł-KIT/CŁ/2023, titled “Automation of Production Processes for Wind Tower Components Including Recycling and Post-Production Waste Management Technologies”, aims at designing and implementing a fully automated line for the cleaning of large-scale castings.

With the rapidly increasing population and the impact of climate change, green construction materials are evolving into sustainable alternatives. Cross-laminated timber (CLT) is gaining attention as a sustainable alternative to traditional construction materials due to its numerous advantages, such as high prefabrication potential, reduced construction time, seismic safety, and a favourable strength-to-weight ratio, as well as being a potential carbon sink. Even though hardwood CLT has better mechanical performance, it is still underutilised compared to softwood CLT. This is mainly because of the bonding challenges due to their variations in densities and anatomical structures. Three-layer CLT panels were produced utilising maple for the outer layers and poplar for the core, employing one-component polyurethane (PUR) adhesive without edge gluing with two different pressure levels—0.6 MPa and 1.0 MPa—using a hydraulic press. Delamination tests were performed on specimens of two dimensions, 70 × 70 × 60 mm and 100 × 100 × 60 mm (length × width × height), following EN 16351:2015. Forty specimens were evaluated for percentage wood failure. Results demonstrated that both smaller specimen size and bonding pressure significantly affected delamination, with 1.0 MPa achieving the most consistent bond integrity. The lower specimen size reduces the amount of delamination by reducing the exposed surface area to the vacuum-pressure delamination method. The findings highlight that optimal bonding pressure is critical for hardwood-based CLT production, with implications for improving manufacturing protocols and expanding the commercial viability of hardwood CLT in load-bearing applications.