No 4 (2024)

In the study and analysis of additive technologies, special attention is paid to increasing the productivity and quality of printed products. However, to improve the 3D printing productivity, it is impossible to increase simply the speed of the squeegee without changing its shape or type. In this case, the quality of the powder layer may suffer, which will lead to a deterioration in the qualities of the final part. To study the effect of roller characteristics on the powder layer deposition, a series of computer simulations of simulation models was carried out. The effect of roller characteristics on the powder layer applying, was assessed, for roller diameters of 30, 50, 70, 100, 150, 200, 250, 300 mm. The simulation was carried out with three application methods: by a rotating and non-rotating roller, as well as by a rotating roller with additional powder feed. It was determined that when applying a layer with a rotating roller with additional powder feed, it is possible to achieve constancy of the forces acting on the roller. This can positively affect the homogeneity of the applied layer. The application of a layer by a rotating roller with additional powder feed is most suitable for 3D printers with a large print area. This method allows avoiding the movement of a large mass of powder over the previous layer, which positively influences the quality of the final part. The study revealed the influence of roller characteristics on the deposition of a powder layer. In particular, with an increase in the roller diameter from 30 to 300 mm, the peak force value also increases. With an increase in the roller diameter by 7.9 %, the powder layer density also increases. It was found that the non-rotating roller is affected by the greatest force, and the forces acting on the rotating rollers differ slightly. A rotating roller, without adding powder, creates the densest layer and allows achieving a powder layer compaction of 5.35 %.

The authors have studied for the first time the phase composition, microhardness and fine structure of the VT23 (α+β)-titanium alloy, with stable and metastable β-phase, after torsional deformation in a Bridgman chamber under a pressure of 4 GPa at room temperature. It has been found that the alloy microhardness, depending on the true degree of deformation under high hydrostatic pressure, changes along a curve with a maximum. The role of stress-induced βm→α" martensitic transformation in the formation of alloy structure, and microhardness under high-pressure torsion was revealed. The highest microhardness of the alloy with stable β-phase was 395 HV 0.05, and with metastable – 470 HV 0.05. At the same time, the maximum microhardness of metastable alloy, compared to stable alloy, was shifted to the region of lower true strain е=2.6. Using X-ray diffraction analysis, and transmission electron microscopy methods, made it possible to trace the evolution of alloy structure under high-pressure deformation consisting in grinding of α-, and α"-phase plates compared to the quenched state, as well as in the development of deformation βm→α", and α"→βm martensitic transformations. An increase in the degree of deformation by high-pressure torsion to е=7.7...7.9, regardless of the deformation stability of the β-phase, leads to a decrease in the alloy microhardness to a level of 185...205 HV 0.05. This is associated with the development of the dynamic recrystallisation process, and the formation of equiaxed α-phase nanoparticles with a size of 20...50 nm. The differences in the loading-unloading curves revealed by kinetic indentation, corresponded to the nature of the change in the VT23 alloy microhardness, depending on the quenching temperature and the true deformation degree.

The use of magnetron sputtering systems with extended uncooled targets will allow developing industrial import-substituting technologies for the formation of thermal barrier coatings, based on zirconium oxide doped with rare earth metal oxides to solve urgent problems of gas turbine construction. This paper presents the results of comparing the technology for producing thermal barrier coatings by magnetron sputtering, with two types of extended targets made of Zr–8%Y alloy – a widely used cooled target and an uncooled extended target, of a magnetron sputtering system developed by the authors. This paper gives a comparison of the results of mass-spectrometric studies of the hysteresis of the oxygen partial pressure inherent in the technology for producing oxide films; the influence of the target type on the coating growth rate; studies of the structure of thermal barrier coatings using the scanning electron microscopy method; and the elemental composition of coatings based on zirconium dioxide partially stabilised with yttrium oxide – YSZ. It has been experimentally found that increasing the temperature of the magnetron sputtering system target, allows decreasing the loop width of the characteristic hysteresis of the oxygen partial pressure dependence on its flow rate by 2 times. The obtained dependencies allowed determining the range of oxygen flow rates at various magnetron discharge powers, at which the work can be performed with stable and sustainable process control, without the risk of falling into hysteresis. The conducted metallographic studies showed a characteristic developed porous dendritic structure of the ceramic layer, which is necessary to reduce the thermal conductivity coefficient of the thermal barrier coating. It has been revealed that the use of an uncooled target allows increasing the deposition rate of the thermal barrier coating by more than 10 times compared to the deposition rate for a cooled target. The obtained results demonstrate the possibility of using the magnetron sputtering technology of an extended uncooled target to form a ceramic layer of thermal barrier coatings.

The work presents a new method of equal channel angular pressing (ECAP) using powerful ultrasonic vibrations (UV). The authors have developed an original device of ultrasonic ECAP, in which the waveguide with the matrix are made as a single unit, and the waveguide fastening elements are located in the nodal plane of mechanical displacements of the standing wave, the excitation of which occurs directly in the matrix and the blank during pressing. For the first time, it has been proposed to transmit ultrasonic vibrations to the zone of intersection of the matrix channels through which the blank moves, not through the punch, but by exciting vibrations in the matrix itself, i. e. the matrix is simultaneously a waveguide for longitudinal ultrasonic vibrations. This allowed increasing repeatedly the efficiency of ultrasonic action by reducing the friction forces between the surface of the blank and the surface of the matrix channels, as well as by reducing the deformation forces in the zone of intersection of the matrix channels, where a simple shift of the deformed metal occurs. As a result, in comparison with the known methods of ultrasonic ECAP, when the reduction in pressing force is less than 15 %, the excitation of ultrasonic vibrations directly in the waveguide – matrix allowed reducing the pressing force by 1.5–4 times. At the same time, the structure of the pressed materials also changes significantly: the grain size and their crystallographic orientations decrease, the microhardness increases. Changes in the phase composition for all samples produced by ECAP with ultrasonic vibrations, and by conventional technology are not observed.

This study examined the influence of alloy composition (mild steel and aluminium) on several machining parameters, such as temperature, cutting force, surface roughness, and chip morphology. Significant variations in these parameters were detected by modifying the alloys while maintaining constant process conditions. In mild steel, rotating speed affected chip morphology, with elevated speeds resulting in continuous chips and reduced rates yielding shorter chips. The augmented rake angle affects the chip properties, resulting in a little decrease in chip length. Moreover, the cutting force influenced the chip length at a designated rotational speed. Conversely, aluminium alloys continuously generated continuous chip fragments irrespective of cutting speed or rake angle. Favourable correlation coefficients are noted among the variables, and a regression model is effectively developed and utilized on the experimental data. The random forest model indicates that material selection significantly influences temperature, cutting force, surface roughness, and chip morphology during machining. This study offers significant insights into the correlation between tool rake angle and other machining parameters, elucidating the elements that influence surface quality. The results enhance comprehension of machined surface attributes, facilitating the optimization of machining operations for various materials.