Influence of Obtaining Conditions on Microstructure, Phase Composition and Properties of Eutectic Alloy of WC–W2C System

The influence of the obtaining conditions on microstructure, phase composition and proper ties of eutectic alloy of the WC–W2C system (relit), which is widely used as a surfacing material to strengthen the wearing parts, was installed. Using scanning electron microscopy, X ray diffraction and durometric analyzes, it was found that the increase in mechanical properties is satisfactorily correlated with a decrease in the ratio between the number of phases of W2C, WC and WC1–x, the thickness of the phase layers in the grains, and the elongation of the latter

The structure and properties of the molybdenum-doped WC–W2C eutectic alloy depending on the production method

Translated from Poroshkova Metallurgiya, Vol. 58, Nos. 1–2 (525), pp. 48–56, 2019. Original article submitted July 9, 2018.Scanning and transmission electron microscopy and X-ray diffraction have revealed that the eutectic 5 wt.% Mo-doped WC–W2C alloy changes its cooling rate in the melt crystallization process when produced in the Tammann furnace, by electron-beam evaporation, and by centrifugal sputtering. This increases the size of phase components by a factor of 2 to 2.5, decreases the number of phases, and reduces compressive stresses (in the W2C matrix) and tensile stresses (in the WC, Mo2C, and (W, Mo)2C inclusions) to 50% and more. These changes result in one and a half times higher hardness and two times higher strength of doped relit, which is widely used for surfacing machine parts and mechanisms operating in conditions of abrasive wear and high dynamic loads

Effect of Molybdenum Additions on the Microstructure and Properties of WC-W2C Alloys

Translated from Poroshkovaya Metallurgiya, Vol. 53, No. 3–4 (496), pp. 121–128, March-April, 2014.The paper examines how additions of 5, 10, and 20 wt.% molybdenum influence the structure, stress–strain state, phase composition, and size of phase components in WC–W2C alloys. It is found that 5 wt.% molybdenum leads to 30% increase in the microhardness and twofold to threefold increase in the wear resistance of cast tungsten carbide compared to the alloy without additions. Higher molybdenum content of the WC–W2C alloys changes the phase composition and increases compressive stresses in the W2C matrix phase and tensile stresses in WC, (Mo, W)2C, and Mo2C inclusions

Modeling of wood surface ignition by wildland firebrands

The probability of structural ignition is dependent both on physical properties of materials and the fire exposure conditions. In this study, the effect of firebrand characteristics (i.e., firebrand size, number of firebrands) on wood ignition behavior was considered. Mathematical modeling and laboratory experiment were conducted to better understand the conditions of wood ignition by a single or group of firebrands with different geometry. This model considers the heat exchange between the firebrands, wood layer and the gas phase, moisture evaporation in the firebrands and the diffusion gases of water vapor in the pyrolysis zone. In order to test and verify the model, a series of experiments to determine probability and conditions for ignition of wood-based materials (plywood, oriented strand board, chipboard) caused by wildland firebrands (pine twigs with a diameter of 6–8 mm and a length of 40 ± 2 mm) were conducted. The experiments investigated the firebrand impact on the wood layer under different parameters, such as firebrand size and quantity, wind speed, and type of wood. The results of experiments showed that the increase in wind speed leads to the increase in probability of wood ignition. Based on the received results, it can be concluded that the ignition curve of wood samples by firebrands is nonlinear and depends on the wind speed and firebrand size as well as their quantity. At the same time, there is no ignition of wood samples in the range of wind speed of 0–1 m/s. The ignition of wood is possible with a decrease in the distance between the firebrands with a decrease in the firebrand length. This result agrees more closely with the model

Optimization of the sintering parameters for materials manufactured by powder injection molding

Translated from Poroshkova Metallurgiya, Vol. 59, Nos. 1–2 (531), pp. 32–41, 2020. Original article submitted September 13, 2019.The properties of sintered and heat-treated steels produced from the Catamold 8740 material by powder injection molding were examined. Parts made of the Catamold 8740 low-alloy mild carbon steel are used in the military, automotive, and other industries where high reliability and resistance to dynamic loads are required. The Catamold 8740 chemical homogeneity was studied as a function of powder injection molding parameters: heating rate, sintering temperature, holding time, and subsequent heat treatment. Microscopic analysis showed that Catamold 8740 was a mechanical mixture of powders in various sizes (carbonyl iron, nickel, Fe–Mo, Fe–Cr, Fe–Si-Mo, Fe–Si). When the heating rate of the Catamold 8740 powder mixture increased from 2 to 5 °C/min, the microstructural heterogeneity caused by uneven compaction decreased and the alloy formation process activated at 900–1340°C. The impact strength of Charpy V-notch test samples changed from 10.39 to 11.52 J/cm2 with higher sintering temperature and heating rate increasing from 2 °C/min (1270°C) to 5 °C/min (1340°C). When holding time increased from 30 to 90 min at a sintering temperature of 1340°C, the material became denser, the pores rounded, and the ferrite matrix homogeneous. However, the impact strength decreased by a factor of 1.4 because of coarser grain sizes and brittle fracture. Heat treatment processes reduced the impact strength after sintering. The results obtained were used to optimize the powder injection molding parameters. The influence of chemical and dimensional inhomogeneity of the starting Catamold 8740 powders and sintering kinetics on the structure and mechanical properties of parts operating under impact loads was established

Effect of Plating of Carbon Fibres with Ni on Properties of Fe-Based Materials

У роботі досліджено формування структури та властивості матеріалу на основі карбонільного заліза, армованого вуглецевими волокнами, попередньо плакованими нікелем. Для першої партії зразків було застосовано неплаковані вуглецеві волокна, а для другої — вуглецеві волокна, плаковані нікелем. Встановлено, що плакування нікелем забезпечує кращу адгезійну взаємодію між вуглецевими волокнами та залізом. Показано, що армування вуглецевими волокнами, плакованими нікелем, уможливлює збільшити як границю міцності, так і пластичність матеріалів. Для зразків, спечених за 900С, міцність зростає непринципово — від 661 МПа до 697 МПа, однак відносне видовження збільшується вдвічі — від 22,7% до 45,1%. Методом фрактографічної аналізи встановлено в’язкий характер руйнування зразків і показано, що мікрорельєф поверхні характеризується косими зламами, що зумовлено утворенням в’язких ямок під дією дотичних напружень. Збільшення температури спікання до 1000С забезпечує зростання міцності на стиснення зразків до 1002–1185 МПа; зразки, які містять плаковані волокна, мають міцність, на 180–185 МПа вищу за міцність зразків з вуглецевими волокнами, неплакованими нікелем.The structure and properties of the material based on carbonyl iron rein forced with carbon fibres, which are previously plated with nickel, are studied. Uncoated carbon fibres are used for the first group of samples, and nickel-plated carbon fibres are used for the second group. Nickel plat ing is found to provide better adhesive interaction between carbon fibres and iron. As shown, the reinforcement with nickel-plated carbon fibres allows increasing both the strength limit and the plasticity of materials. At the same time, for samples sintered at 900C, the strength does not increase fundamentally (from 661 MPa to 697 MPa), but the relative elongation doubles from 22.7% to 45.1%. Using the method of fracto graphic analysis, the viscous nature of the destruction of the samples is established, and it is shown that the microrelief of the surface is charac terized by oblique fractures, which is due to the formation of viscous dimples under the action of tangential stresses. An increase in the sintering temperature to 1000C provides an increase in the compressive strength of the samples to 1002–1185 MPa, while the samples containing clad fibres have strength of 180–185 MPa higher than the strength of samples with carbon fibres not plated with nickel

Влияние механических колебаний на формирование микроструктуры монокристаллов и керамических композитов при выращивании с расплава

Досліджено вплив механічних коливань частотою 50 Гц на процес формування мікроструктури та хімічного складу монокристалів із гексабориду лантану й армованих керамічних композитів системи LaB₆—ZrB₂ під час кристалізації із розплаву та подальшої термообробки. Встановлено, що механічні коливання впливають на процес кристалізації і призводять до вирівнювання концентраційного профілю розподілу атомів перед фронтом росту кристала, змінюють форму та розміри зони розплаву, а також підсилюють структурну неоднорідність. Методами оптичної мікроскопії, рентгенівської текстурдифрактометрії, мікрорентгеноспектральним і рентгенофазовим аналізами показано, що внаслідок дії механічних коливань змінюється кількість, розмір і форма волокон дибориду перехідного металу в процесі спрямованої кристалізації евтектичного сплаву LaB₆—ZrB₂. З’являється розорієнтація матричної і армуючої фаз відносно кристалографічного напрямку росту, що задається кристалом-затравкою, яка призводить до погіршення монокристалічності зразка. Підвищується дефектність структури, що своєю призводить до зменшення періоду ґратки і густини гексабориду лантану та керамічного композиту системи LaB₆—ZrB₂.The effect of mechanical vibration with 50 Hz frequency on the formation of microstructure and chemical composition of single crystals of lanthanum hexaboride and reinforced ceramic composites of LaB₆—ZrB₂ during crystallization from the melt and subsequent heat treatment was investigated. It was found that the mechanical vibrations affect the crystallization and lead to the equalization of the concentration profile of the distribution of atoms in front of the crystal growth, alter the shape and size of the melt zone and increase structural heterogeneity. Methods of optical microscopy, X-ray texture diffractometry, microanalysis and X-ray analysis show that as a result of mechanical vibrations changing the number, size and shape of the transition metal diboride fibers during directional solidification of eutectic alloy LaB₆—ZrB₂ occurs. Disorientation matrix and reinforcing phases relative to crystallographic growth direction, given by the seed crystal, which leads to poor monocrystallinity sample, appear. Increasing of the defect structure reduces the lattice period and density of lanthanum hexaboride and ceramic composite system LaB₆—ZrB₂.Исследовано влияние механических колебаний частотой 50 Гц на процесс формирования микроструктуры и химического состава монокристаллов с гексаборида лантана и армированных керамических композитов системы LaB₆—ZrB₂ при кристаллизации из расплава и последующей термообработке. Установлено, что механические колебания влияют на процесс кристаллизации и приводят к выравниванию концентрационного профиля распределения атомов перед фронтом роста кристалла, изменяют форму и размеры зоны расплава, а также усиливают структурную неоднородность. Методами оптической микроскопии, рентгеновской текстурдифрактометрии, микрорентгеноспектральным и рентгенофазовым анализами показано, что в результате действия механических колебаний изменяются количество, размер и форма волокон диборида переходного металла в процессе направленной кристаллизации эвтектического сплава LaB₆—ZrB₂. Появляется разориентация матричной и армирующей фаз относительно кристаллографического направления роста, задающегося кристаллом-затравкой, которая приводит к ухудшению монокристалличности образца. Повышается дефектность структуры, что в свою очередь приводит к уменьшению периода решетки, а также плотности гексаборида лантана и керамического композита системы LaB₆—ZrB₂

Thermography of flame during diesel fuel combustion with steam gasification

The paper represents a study concerning the combustion of liquid hydrocarbon fuel in a perspective burner device with the controlled forced supply of overheated steam into the combustion zone, using diesel fuel. The thermal imaging measurements are conducted for the outer flame of the burner device in the wide range of regime parameters (flow rate and temperature of steam). A thermal imaging camera (FLIR, JADE J530SB) is used in the experiments. The effective emissivity coefficient of flame is obtained versus the flow rate of steam supplied. The steam parameters are found to influence on the temperature in the outer flame of the burner device

Travelling on Graphs with Small Highway Dimension

We study the Travelling Salesperson (TSP) and the Steiner Tree problem (STP) in graphs of low highway dimension. This graph parameter was introduced by Abraham et al. [SODA 2010] as a model for transportation networks, on which TSP and STP naturally occur for various applications in logistics. It was previously shown [Feldmann et al. ICALP 2015] that these problems admit a quasi-polynomial time approximation scheme (QPTAS) on graphs of constant highway dimension. We demonstrate that a significant improvement is possible in the special case when the highway dimension is 1, for which we present a fully-polynomial time approximation scheme (FPTAS). We also prove that STP is weakly NP-hard for these restricted graphs. For TSP we show NP-hardness for graphs of highway dimension 6, which answers an open problem posed in [Feldmann et al. ICALP 2015]