Materials Science Forum Vol. 1040

Abstract: The article presents the results of a study of diffusion chromium plating of stainless steel X20Cr13 by iodine transport. The main kinetic laws of the process - the effect of temperature and time of chromium plating on the thickness of the coatings - have been studied. It is shown that the main phases of the coating are chromium carbides and nitrides with surface microhardness HV up to 15 GPa. The tribotechnical properties of the obtained coatings on rollers - friction pairs are determined.

Abstract: The paper presents the results of the determination of the effect of a photocatalytic composite material (PCM) with the composition SiO₂‒TiO₂ on the main properties of white Portland cement: heat release during hydration, phase composition and microstructural features of cement stone, pressure strength and self-cleaning ability. PCM was synthesized by a sol-gel method based on tetrabutoxytitanium and finely dispersed diatomite powder and 15% cement was added instead. The presence of PCM in the cement system provided the reduction of the induction period of cement hydration, consolidation of the microstructure of the cement stone with the products of the pozzolanic reaction, the ability to photocatalytic self-cleaning of the cement stone surface.

Abstract: The paper presents the results of the assessment of the effect of bacterial microorganism Sporosarcina pasteurii and CaCl₂ and CH₄N₂O precursors as agents initiating carbonate mineralization processes on the construction and technical properties of binders. In order to achieve this, a preliminary bacterial solution with precursors was prepared, which was introduced into the system instead of mixing water in the range of 0–10% with interval of 2%. The effect of the bacterial solution as a complex additive on the physical and mechanical properties of cement paste and stone is shown: normal density, setting time, water segragation, strength in compression and bending. The introduction of the solution provides a reduction in the setting time of cement without loss of strength both at the initial and at the final stages of hardening.

Abstract: The existing methods of confering hydrophobic properties to various building materials are considered. Obtaining special, including hydrophobic, properties of water-emulsion paints is a very relevant task. Previously, a method was developed for producing an emulsion of a polysiloxane stabilized with polyvinyl alcohol. The paper describes the possibility of using a hydrophobisating emulsion of polyhydrosiloxane as a functional additive for an acrylic water-dispersion paint. This emulsion is capable of forming coatings on dense and porous surfaces with an adjustable contact angle up to 105 °. The use of this emulsion, with its sufficient coalescence for volumetric hydrophobization of coatings, makes it possible to obtain a high contact angle on the surface. In the paper, it was assumed that the partial introduction of small amounts (up to 10 %) of a hydrophobizing emulsion into water-dispersion paints would allow achieving the contact angle of wetting for similar coatings consisting exclusively of emulsion. It is shown that the introduction of small amounts of a hydrophobizing emulsion with an auxiliary coalescing action of ethylene glycol makes it possible to impart hydrophobic properties to the surface of the resulting coating. When the optimum concentration of ethylene glycol in the coating is reached, dissolution and transport (yield) of polysiloxane to the surface is ensured. The research carried out made it possible to develop a paint composition with a hydrophobizing emulsion with a contact wetting angle of about 100 °, which ensured the hydrophobicity of the previously hydrophilic coating of a water-dispersion acrylic paint.

Abstract: Powders of X6CrNiTi18-10 stainless steel were fabricated from original workpieces of different grade by gas atomization method. It was found that it is necessary to use argon as a gas for gas atomization of X6CrNiTi18-10 steel, since the use of nitrogen leads to the formation of its compounds, namely, titanium nitride. It is shown that all used workpieces – electric arc, electric slag and vacuum arc refinement – allow one to obtain powders suitable for further utilization in selective laser melting technology of 3D printing. The main physicochemical and technological properties of the obtained powders have been investigated. Changes in the chemical composition and quality of the powders are not significant within the X6CrNiTi18-10 grade. The 0...20 μm fraction of powders does not have fluidity, and thus cannot be used for additive technologies. The fraction 20...63 μm have suitable rheological properties for additive technologies and may be used in selective laser melting (SLM) process. The yield of target fraction 20 ... 63 microns was ≈45%. The fraction 63...120 μm may be used for the direct metal deposition (DMD) additive technology. Considering the economic aspect of the technology, it is preferable to use original workpieces of X6CrNiTi18-10 steel produced by electric arc or electroslag process, since the market price of vacuum arc steel is significantly higher. The fraction of ferrite phase in the powder increases with a decrease of particle size of the resulting powder and is lower comparing to the original workpiece. In the future, for a detailed study of the technological properties, it is planned to grow samples from each type of the obtained powders on installation for selective laser melting and direct laser deposition to determine the physical and mechanical properties of fabricated samples (tensile and impact bending tests) and carry out metallographic studies.

Abstract: Today 3D printing with ceramics is a promising direction in the development of additive technologies. In this work, we have developed a technology for printing with ceramic pastes based on aluminum oxide and wax, namely: an extruder for printing with ceramic pastes was modeled and manufactured, the composition of the slip was selected and the paste for printing was made. After choosing the print parameters, test samples were printed: a disk and a box. Since 3D printing with ceramics is just one of the stages of manufacturing ceramic products, then we selected the parameters for drying and sintering the raw material. Drying of products is necessary to burn off an excess amount of a binder (paraffin), and due to sintering; the raw material acquires final strength and mechanical characteristics. After sintering, the sintering parameters and physical and mechanical properties of the products were measured. The microstructure of the printed products was studied using scanning electron microscopy. The phase change during sintering was studied by X-ray analysis. All obtained properties were compared with a reference sample (corundum tile made of aluminum oxide of the same grade, but using traditional ceramic technology, including pressing, drying and sintering of the product). In terms of all properties, the printed ceramics are not significantly inferior to the reference sample; however, in general, the additive technology has more advantages, such as a wide variety of shapes, shorter manufacturing time for parts, and lower energy costs.

Abstract: The article presents the results of a study of the physical and mechanical properties of cellular structures fabricated by means of additive manufacturing. The structural elements are repeating in three directions, and have a geometric shape of Schwarz-P surface. Samples in the form of a cube (size 30x30x30 mm) were created by layer-by-layer fusion of thermoplastic polymer on a FDM (Fused Deposition Modeling) 3D printer. Compression tests of samples with different geometry have shown that with an increase in the characteristic size of a repeating structural element with a decrease in the parameter (t), the strength of the samples increases and is maximal at t = -0.6. According to the calculations performed by the finite element method, this is associated with an increase in the area of ​​the dangerous section. However, specimens with t = 0 have the highest specific strength. This is because the average curvature of products with t = 0 is zero at each point, which contributes to the effective distribution of mechanical stresses in the specimen. When t ≠ 0, the average curvature is constant, but has a non-zero value.

Abstract: The article deals with the problems of withstanding harsh temperatures by steel and iron. The authors of the work discuss iron denser high-temperature of γ modification and maximums and minimums of impact. In addition, the article analyses the transformations of iron and anomalies of properties: peak of heat capacity, acceleration of diffusion, etc. The authors take into account the consensus on the causes of polymorphism and the theoretical model of ferromagnetism. Besides, there is a consideration of "transformation" in interaction between Fe atoms that produce anomalies of steel properties. It is necessary to note the transformation detected by anomalies of any properties including mechanical. In the presented work the authors have made an attempt to prove transformations in iron at ~650 °C on the basis of extreme values of hardness and microhardness, metallographic structure, parameters of fine structure, precipitation resistance force depending on temperature. Therefore, the analysis of literature sources on physical and mechanical properties of iron and its derivatives has been made.