Fjodor Sergejev

Additive manufacturing (AM), commonly known as 3D printing, has emerged as a transformative technology in the field of manufacturing, offering unprecedented flexibility in creating complex geometries. This study investigates the practical application of AM in producing patterns for investment casting using plaster molds for aluminum components. The primary objective is to identify suitable filament materials for printing patterns that can meet the demands of the casting process while ensuring high-quality aluminum castings. As the process of investment casting in plaster molds involves burning out the pattern, it is important that the burn-out process of the 3D-printed pattern leaves as little residue as possible in the mold. An experimental approach was adopted to evaluate various polylactic acid (PLA) filament materials. Each material was assessed based on the amount of residue remaining after the burn-out process during mold making. The results indicated that some types of PLA filaments behave considerably differently from others. Some filaments leave significantly less residue and can ensure better casting quality. The study provides suggestions for using low-cost filament extrusion-based 3D printers in the plaster mold casting of aluminum products. The findings contribute to the broader adoption of AM in foundry applications by providing insights into material selection and process optimization. Future work will focus on refining the balance between print efficiency and casting quality.

The circularity of polymer waste is an emerging field of research in Europe. In the present research, the thermal, surface, mechanical, and tribological properties of polypropylene (PP)-based composite produced by injection molding were studied. The pure PP matrix was reinforced with 10, 30, and 40% wt. of pure cotton, synthetic polyester, and polyethylene terephthalate post-consumer fibers using a combination of direct extrusion and injection molding techniques. Results indicate that PP-PCPESF-10% wt. exhibits the highest value of tensile strength (29 MPa). However, the values of tensile and flexural strain were lowered with an increase in fiber content due to the presence of micro-defects. Similarly, the values of modulus of elasticity, flexural modulus, flexural strength, and impact energy were enhanced due to an increase in the amount of fiber. The PP-PCCF-40% wt. shows the highest values of flexural constant (2780 MPa) and strength (57 MPa). Additionally, the increase in fiber loadings is directly proportional to the creation of micro-defects, surface roughness, abrasive wear, coefficient of friction, and erosive wear. The lowest average absolute arithmetic surface roughness value (R_a) of PP and PP-PCCF, 10% wt., were 0.19 µm and 0.28 µm. The lowest abrasive wear value of 3.09 × 10⁻⁶ mm³/Nm was found for pure PP. The erosive wear value (35 mm³/kg) of PP-PCCF 40% wt. composite material was 2 to 17 times higher than all other composite materials. Finally, the single-step analysis of variance predicts reasonable results in terms of the p-values of each composite material for commercial applications.

In the present study, TiC-Fe cermets were fabricated through selective laser melting (SLM) for the first time employing pulse wave using a pulse shaping technique and regular laser pulse wave. Two samples were fabricated each with adapting pulse shaping technique and regular laser pulse wave with varied laser peak power and exposure time to obtain an optimized parameter. The pulse shaping technique proves to be an optimal method for fabrication of the TiC-Fe-based cermet. The effect of the laser peak power and pulse shaping on the microstructure development was investigated through scanning electron microscopy and X-ray diffraction analysis. Two-phased microstructures revealed the distribution of TiC and Fe. A maximum hardness and fracture toughness of 1010 ± 65 MPa and 16.3 ± 1.7 MPa m ^1/2 , respectively, were observed for the pulsed-shaped samples illustrating that pulse shaping can be an effective way to avoid cracking in brittle materials processed by SLM.

The focus is on the oxidation resistance and tribological performance of ta-C and Al₂O₃/ta-C coatings. The wear tests were carried out on the ball on disc tribometer at room (25 °C) and high (400, 450 and 500 °C) temperatures in ambient air with Si₃N₄ balls as counterbodies. Scanning electron microscopy and Raman spectroscopy were used to analyze the surface morphology and chemical bonding, respectively. The Al₂O₃/ta-C coating exhibited better oxidation resistance and tribological performance at elevated temperatures than the ta-C coating. The Raman analysis revealed that a thin alumina layer suppresses structural changes in the ta-C coating at elevated temperatures, thus preserving the sp³ content.

The influence of laser pulse shaping on the formation of TiC-Fe-based cermets with different laser process parameters is investigated. The impact of pulse shaping and laser melting peak power on the microstructural development and mechanical properties of SLM-built parts is addressed. This research focuses primarily on the process parameters required to produce crack-free components and includes investigations of mechanical properties such as microhardness and fracture toughness. To acquire optimal process parameters, samples were manufactured using pulse shaping technology with varying laser melting peak power and exposure time. The influence of laser melting peak power and pulse shape on microstructure development and phases was analyzed using a scanning electron microscope and X-ray diffraction.

High Pressure Torsion Extrusion (HPTE) as a novel approach in mechanical nanostructuring of metallic materials and alloys has the potential to be utilized in industrial applications due to its unique features in fabricating bulk-nanostructured materials with enhanced mechanical and functional properties. Three different HPTE regimes based on the extrusion speed of the punch (v, mm/min) and rotational speed of the die (ω, rpm) were used in this work: v7w1, v1w1, and v1w3. The grain refinement obtained by this technique was outstanding since the initial grain size of 120 μm in annealed conditions was reduced to the final grain size of 0.7 μm in v1w3 in merely one pass of extrusion; however, each regime showed a different level of grain refinement depending on the imposed strain. Examination of the tribological properties by reciprocal wear testing in dry conditions revealed no significant change in the coefficient of friction; nevertheless, the mechanism of the wear from adhesion shifted to abrasion and the amount of displaced volume decreased. This modification is associated with the improvement of hardness and the reduction of plasticity in materials that confined the plastic shearing. Increasing the induced strain by changing the HPTE regimes decreased the overall displaced volume and reduced the built-up edge around the wear track.

The study investigates thermal stability and high temperature tribological performance of a-C:H:Si diamond-like carbon (DLC) coating. A thin alumina layer was deposited on top of the a-C:H:Si coating to improve the tribological performance at high temperatures. The a-C:H:Si coating and alumina layer were prepared using plasma-activated chemical vapour deposition and atomic layer deposition, respectively. Raman and X-ray photoelectron spectroscopy were used to investigate the structures and chemical compositions of the specimens. The D and G Raman peaks due to sp² bonding and the peaks corresponding to the trans-polyacetylene (t-Pa) and sp bonded chains were identified in the Raman spectra of the a-C:H:Si coating. Ball-on-disc sliding tests were carried out at room temperature and 400 °C using Si₃N₄ balls as counter bodies. The a-C:H:Si coating failed catastrophically in sliding tests at 400 °C; however, a repeatable and reproducible regime of sliding with a low coefficient of friction was observed for the Al₂O₃/a-C:H:Si coating at the same temperature. The presence of the alumina layer and high stress and temperature caused structural changes in the bulk a-C:H:Si and top layers located near the contact area, leading to the modification of the contact conditions, delivering of extra oxygen into the contact area, reduction of hydrogen effusion, and suppression of the atmospheric oxidation.