Dmitriy A. Tkachev

AlMgB₁₄ and AlMgB₁₄–50 wt % TiB₂ coatings deposited onto a VK-8 hard-alloy substrate by ion-plasma sputtering using powder ceramic targets are studied. It is established that the formed coatings are characterized by an amorphous-crystalline structure containing B–B, B–O, and Ti–O interatomic bonds. The composition of the target has a minor effect on the morphology and roughness of the obtained coatings. The hardness of TiB₂-free coatings reaches 35 ± 2 GPa at the lowest friction coefficient of 0.12. It is established that the coatings formed using the AlMgB₁₄–50 wt % TiB₂ target possess higher adhesion strength and wear resistance.

The article considers the process of formation of cracks in ceramic-metal boards in the zone of localization of interlayer vias formed on the basis of tungsten two-fraction metallization pastes with an average particle size of 0.9 and 2.0 μm, which provide electrical connection between the switching layers of microcircuit packages. A study was made of the influence of the "form factor" of interlayer vias, their structure and placement density on the process of cracking of ceramic-metal boards. The size effect of the direct proportional dependence of the temperature shrinkage of interlayer vias on the diameter and density of their placement on the board is revealed, which has a significant effect on the cracking of boards in the zone of interlayer vias. It has been established that the fineness of the powder filler of the paste intended for the formation of interlayer vias has a significant effect on the degree of consistency between the temperature shrinkage of ceramics and the interlayer via, and hence on the magnitude of stresses at the boundary of the system of elements under consideration, which contribute to the formation of microcracks. It was revealed that the toroidal shape of the interlayer via, characterized by the presence of a cylindrical cavity, which in turn is the initiator of tangential stresses in the volume of the transition, leads to the formation of microcracks. At the same time, continuous interlayer vias have an increased resistance to temperature effects, but do not exclude the possibility of microcracks formation at the “ceramics - interlayer via” boundary. The conditions for the formation of interlayer vias of a toroidal shape with a diameter of 0.1 to 0.5 mm are considered. The dominating effect of the viscosity of metallizing tungsten pastes in the range from 1000 to 70000 Poise on the possibility of the formation of a cylindrical cavity in the volume of the interlayer via has been established. Practical methods for preventing their occurrence are proposed. An estimate of tangential stresses in the volume of toroidal interlayer transitions is given. It has been proven that the formation of an internal cavity in the center of the interlayer via, during its formation, leads to a decrease in temperature shrinkage by 4% relative to the values of thermal shrinkage of a continuous interlayer via. Comparative analysis of temperature shrinkage was carried out for cermet boards containing interlayer vias from 0.3 to 0.5 mm in their volume. В статье рассмотрен процесс образования микротрещин металлокерамических плат в зоне локализации межслойных переходов, сформированных на основе вольфрамовых двухфракционных металлизационных паст со средним размером частиц 0,9 и 2,0 мкм, обеспечивающих электрическую связь между коммутационными слоями корпусов микросхем. Проведено исследование влияния «форм-фактора» межслойных переходов, их структуры и плотности размещения на процесс трещинообразования металлокерамических плат. Выявлен размерный эффект прямо-пропорциональной зависимости температурной усадки межслойных переходов от диаметра и плотности их размещения на плате, оказывающий значимое влияние на трещинообразование плат в зоне межслойных переходов. Установлено, что дисперсность порошкового наполнителя пасты, предназначенной для формирования межслойных переходов, оказывает значимое влияние на степень согласованности температурных усадок керамики и межслойного перехода, а значит и на величину напряжений на границе рассматриваемой системы элементов, которые способствуют образованию микротрещин. Выявлено, что тороидальная форма межслойного перехода, характеризующаяся наличием цилиндрической полости, которая в свою очередь является инициатором тангенциальных напряжений в объеме перехода, приводит к образованию микротрещин. При этом, сплошные межслойные переходы имеют повышенную устойчивость к температурным воздействия, но не исключают возможность образования микротрещин на границе «керамика – межслойный переход». Рассмотрены условия образования межслойных переходов тороидальной формы диаметром от 0,1 до 0,5 мм. Установлено доминирующее влияние вязкости металлизационных вольфрамовых паст в диапазоне от 1000 до 70000 Пуаз на возможность образования цилиндрической полости в объеме межслойного перехода. Предложены практические методы предотвращения их появления. Приведена оценка...

The paper presents the results of studies of the self-propagating high temperature synthesis (SHS) of boron nitride via chemical reduction of boron oxide with aluminum in a nitrogen medium. The phase composition of the powder reaction products depending on the nitrogen pressure during the synthesis was studied by X-ray diffraction. It was found that SHS in the B₂O₃–Al system gives the BN–Al₂O₃ powder material containing 20–28 wt % hexagonal boron nitride depending on the nitrogen pressure. Microstructure examination showed that the obtained powder materials contains separate hexagonal BN particles with 2O₃ determine the possibility of BN isolation from the obtained powder mixture by the pneumatic powder separation methods.

Digital light processing (DLP) or stereolithography is the most promising method of additive manufacturing (3D printing) of products based on high-energy materials due to, first of all, the absence of a high-temperature impact on the material. This paper presents research results of an ultraviolet (UV)-cured urethane methacrylate polymer containing 70 wt.% of high-energy solid powder based on ammonium salts, which is intended for digital light processing. Polymerization of the initial slurry is studied herein. It is shown that the addition of coarse powder transparency for the UV radiation to resin increases its curing depth. The thickness of the layer, which can polymerize, varies from 600 µm to 2 mm when the light power density ranges from 20 to 400 mJ/cm², respectively. In DLP-based 3D printing, the obtained material density is 92% of the full density, while the compressive strength is 29 ± 3 MPa, and the ultimate tensile strength is 13 ± 1.3 MPa. The thermogravimetric analysis shows the decrease in the thermal decomposition temperature of UV-cured resin with high-energy additives compared to the thermal decomposition temperatures of the initial components separately. Thermal decomposition is accompanied by intensive heat generation. The burning rate of obtained samples grows from 0.74 to 3.68 mm/s, respectively, at the pressure growth from 0.1 to 4 MPa. Based on the results, it can be concluded that DLP-based 3D printing with the proposed UV photocurable resin is rather promising for the fabrication of multicomponent high-energy systems and complex profile parts produced therefrom.

The paper presents the results of studies of the self-propagating high temperature synthesis (SHS) of boron nitride via chemical reduction of boron oxide with aluminum in a nitrogen medium. The phase composition of the powder reaction products depending on the nitrogen pressure during the synthesis was studied by X-ray diffraction. It was found that SHS in the B2O3–Al system gives the BN–Al2O3 powder material containing 20–28 wt % hexagonal boron nitride depending on the nitrogen pressure. Microstructure examination showed that the obtained powder materials contains separate hexagonal BN particles with 3 μm size. The differences in the density and morphology of BN and Al2O3 determine the possibility of BN isolation from the obtained powder mixture by the pneumatic powder separation methods.

This paper presents the results of studies on AlMgB₁₄-based ceramic coatings deposited on WC-Co hard alloy substrates using RF plasma sputtering. The aim of this work is to study the structure, phase composition, and mechanical properties of AlMgB₁₄-based coatings depending on the sputtering mode. According to the results of the microstructural study, the bias voltage applied to the substrate during the sputtering process significantly contributed to the formation of the coating morphology. Based on the results of compositional and structural studies by energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy, it was found that the coatings are composed of nanocrystalline B₁₂ icosahedrons distributed in an amorphous matrix consisting of Al, Mg, B, and O elements. The nanohardness of the coatings varied from 24 GPa to 37 GPa. The maximum value of the hardness together with the lowest coefficient of friction (COF) equal to 0.12 and wear resistance of 7.5 × 10⁻⁵ mm³/N·m were obtained for the coating sputtered at a bias voltage of 100 V. Compared with the COF of the original hard alloy substrate, which is equal to 0.31, it can be concluded that the AlMgB₁₄-based coatings could reduce the COF of WC-based hard alloys by more than two times. The hardness and tribological properties of the coatings obtained in this study are in good agreement with the properties of AlMgB₁₄-based materials obtained by other methods reported in the literature.

AlMgB₁₄ materials were obtained by hot-pressing of the prereacted AlMgB₁₄ powder. The phase composition, structure, hardness and flexural strength have been studied. The XRD studies shown that the phase composition of the obtained materials contains from 9 to 12 wt. % of the spinel MgAl₂O₄ phase except target AlMgB₁₄-phase. The spinel content increases linearly with an increase in the hot-pressing temperature from 1400 °C to 1600 °C. It was found that the density of the studied materials non-linearly depends on the hot-pressing temperature. An increase in the hot-pressing temperature from 1400 °C to 1500 °C leads to an increase in the relative density of the samples from 84% to 93%, respectively. A further increase in the hot-pressing temperature to 1600 °C leads to a decrease in the relative density to 81% due to the complication of the densification processes with an increase in the spinel content. An increase in the relative density from 81% to 93% leads to an increase in the flexural strength from 121 to 314 MPa and an increase in the Vickers microhardness from 5.1 to 7.9 GPa, respectively.