In the paper, a novel technique for highly dispersed pyrochlore Y2Ti2O7 is proposed. The experimental results proved that the application of microwave irradiation at a certain stage of calcination allowed synthesizing of Y2Ti2O7 in much shorter time, which ensured substantial energy savings. An increase up to 98 wt.% in the content of the preferred phase with a pyrochlore-type structure Y2Ti2O7 was obtained after 25 h of yttrium and titanium oxides calcination at a relatively low temperature of 1150 °C, while the microwave-supported process took only 9 h and provided 99 wt.% of pyrochlore. The proposed technology is suitable for industrial applications, enabling the fabrication of large industrial amounts of pyrochlore without solvent chemistry and high-energy mills. It reduced the cost of both equipment and energy and made the process more environmentally friendly. The particle size and morphology did not change significantly; therefore, the microwave-assisted method can fully replace the traditional one.
Al2O3 and Al2O3/ZrO2 multilayer coatings were deposited by the magnetron method by sputtering the corresponding metal targets in a mixture of oxygen and argon gases. The microstructure of the cross sections to determine the thickness and elemental composition of the obtained coatings was studied by transmission and scanning electron microscopy. The surface morphology of Al2O3 coating samples was studied by scanning probe microscopy. It is shown that the formed Al2O3 coating and the Al2O3/ZrO2 multilayer coating have a columnar structure with the columns oriented perpendicular to the surface. The columnar structure of multilayer coatings is not violated during the transition from layer to layer. The coating surface consists of globules with a diameter of about 20 nm. It was found that the Al2O3 coating has dielectric properties using the method of impedance spectrometry. Thus, it was shown that the magnetron method can be used to apply high-quality multilayer dielectric coatings, which can be used as thermal barrier coatings to protect the blades of high-temperature stages of aircraft engine turbines.
Multilayer (TiSi)N/CrN coatings were fabricated through vacuum-arc deposition by applying the arc currents of (100 ÷ 110) A on TiSi cathode and (80 ÷ 90) A on Cr cathode, negative bias potential connected to the substrate holder of –(100 ÷ 200) V and reactive gas pressure of (0.03 ÷ 0.6) Pa. Applying a negative bias voltage on substrates enhanced the ion bombardment effect, which affected the chemical compositions, phase state, mechanical and tribological properties of (TiSi)N/CrN coatings. Obtained results indicated that (TiSi)N/CrN coatings with Si content ranging from 0.53 to 1.02 at. % exhibited a high hardness level of (22.1 ÷ 31.1) GPa accompanied with a high Young’s modulus of (209 ÷ 305) GPa, H/E* level of (0.080 ÷ 0.100), H3/E*2 level of (0.15 ÷ 0.33) GPa, and the friction coefficient of 0.35. Values of critical loads at dynamic indentation, changes in friction coefficient and level of acoustic emission signal evidence the high adhesive strength of (TiSi)N/CrN coatings, which allows recommending them to increase cutting tool performance.
The paper investigates the structure and properties of nanoscale multilayer coatings based on (TiZr)N and (TiSi)N produced by vacuum arc technique. Also, it provides an analysis of the impact of partial pressure of nitrogen on structural and phase state of coatings. The nitride phases are strongly textured, crystallographic planes (111) of most grains are oriented parallel to the surface. Dimensions of the coherent scattering regions and values of micro-distortions of the lattice have been calculated. The hardness of coatings reached 37.1 GPa, and the adhesion fracture load exceeds 150 N. The process technology ensures high uniformity of and a low defect rate in obtained coatings.
The article represents the results of research of various methods of obtainingantifriction material "copper-lead-graphite" by methods of powder metallurgy. With the help of hotvacuum electroconsolidation of powders, which is effective for refractory materials, the conditionsfor separate cold pressing are determined, namely, product formation at 500 MPa and sintering at900 °C, which is more productive for metal powders.The initial formation of the samples was carried out in a collapsible steel mold on a hydraulicpress with a force of up to 200 tons from a mixture of powders of copper, lead and graphite, whichhad dimensions of 60–200 μm. Sintering was performed in a vacuum oven at temperatures of 700–900 °C for 20–30 minutes. To obtain a density of more than 5.6 g / cm3, it is necessary to significantlyincrease the pressure during the formation of powders. During the formation of the dry mixture,compression transverse cracks appear.Liquefied kerosene was selected from the list of studied organic liquids, which allowed to obtainhigh-quality products without cracks with a density of 5.6–5.9 g/cm3 at a load force of about 500 MPa. Sintering was performed in an inert nitrogen environment, which reduced lead losses to2–5 % at temperatures above 700 °С. Nitrogen was first supplied to the vacuum chamber to apressure of 1 atmosphere, and after increasing the temperature in the chamber, the nitrogen pressurerose to 1.2 atm.The hardness of the obtained samples was 42–46 HB according to Brinell (135–150 MPa).Machining of samples with different cutting tools was performed at different speeds and showed goodmachinability. Processed parts during storage have not changed their size. With the help of thedeveloped technology it is possible to produce composite materials with a density of 4.4–6.2 g/cm3and a Brinell hardness of 30–48 HB (99.9–159 MPa).
The results of investigations of multi-component nanostructured coatings of (TiAlSiY)N/CrN type are presented. The influence of different variants of substrate surface pretreatment on adhesive strength and hardness of coatings was studied. Pre-treatment of samples was carried out in plasma of two-stage gas discharge according to various technological schemes. Except for ion-plasma purification, some samples were pretreated with a sublayer of chromium within 5 minutes. The coatings were formed by a vacuum-arc deposition method at simultaneous spraying of two cathode targets. The first cathode is made of chromium, and the second cathode is made of multicomponent Ti - Al - Si - Y alloy obtained by vacuum-arc remelting of powder mixture of the mentioned elements. The coatings were deposited on polished stainless-steel substrates at negative 280 V bias potential. The geometry of the unit and its elements, as well as technological characteristics of the processes of evaporation-condensation were selected so that at a speed of rotation of samples 8 revolutions per minute the formation of the coating with a total thickness of about 9.0 microns occurred in approximately 60 minutes. The analysis of the composition of the coatings shows that the content of elements in the coating differs greatly from the content of elements in the sprayed cathodes. The X-ray diffractometry has shown that all deposition modes are characterized by the formation of phases with cubic (fcc) crystal lattice in both phase layers of multilayer coatings. In the layers formed at spraying of TiAlSiY alloy, a multi-element disordered solid solution (TiAlSiY)N with a crystal lattice of NaCl type and a lattice parameter of 0.4241 nm, as well as chromium mononitride CrN with a lattice parameter of 0.4161 nm, is determined. It has been established that preliminary formation of a chromium sublayer on the substrate leads to significant changes in adhesive strength of multi-component coatings compared to coatings without a sublayer.
Modern scientific and technological development of society, further intensification of production together with the provision of proper safety of human life and preservation of the environment necessitate the search for new solutions in the creation of new materials and technologies. The creation of effective materials for the latest and future technologies and technicaldevices is based on new scientific data on the definition and analysis of specific mechanisms of physicochemical processes that implement the desired structural and phase state of solids with the desired set of properties. In recent decades, the most effective way to control the properties of solid materials is the use of nanotechnology and nanomaterials, which have recently been increasingly used in almost all areas of new technologies. The article investigates synthesis processes, structural characteristics and structural-phase processes in multicomponent metal-ceramic oxide materials, physicochemical mechanisms ofsynthesi s of multielement oxide compounds Y2Zr2O7 with pyrochlor structure during consolidation and sintering of yttrium and zirconium oxides, structure formation -phase characteristics of materials with different chemical composition. The structural-phase evolution in the synthesis of new substances and the consolidation of compounds of the Y2O3 – ZrO2 system have been studied. Samples of oxide heat with the proportion of pyrochlorine phase Y2Zr2O7 up to 41 % were obtained. It is established that the kinetics of increasing the proportion of pyrochlorine phase in the samples indicates a desirable increase in the activity of the chemical reaction, which can be achieved by increasing the synthesis temperature to the temperatures of eutectic formation or increasing the reaction surface of powders.
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