Papers by Keyword: Borides

Abstract: The present research shows the possibility of using an ytterbium nanosecond pulsed fiber laser for wear resistance improvement of carbon and alloy steels. The wear test was performed in accordance with the block-on-ring scheme with dry sliding friction on a friction machine. Surface dispersing/alloying was carried out from a boron carbide paste. This leads to a significant wear resistance improvement of steels. It was revealed that the mass loss during wear test reduced by several times after laser treatment compared to the non-treated samples. The wear mechanism differs depending on the type of steel and largely refers to their microstructure and composition. The tribo-oxide layer forms during the wear test.

Abstract: The paper presents the research results on the production of doped composite materials by the method of out-of-furnace liquid-phase self-propagating high-temperature synthesis using oxides and mineral concentrates containing Zr and W as a charge. The positive experience of producing ingots of intermetallic alloys based on the Ni-Al system in one stage of the reduction process of joint metallothermy is shown. The use of Zr in the charge leads to grinding of microstructure of the ingots and the formation of intermetallic compounds containing Zr. The additional use of C, B₂O₃, and W in the charge results in the formation of complex borides and tungsten carbides in the ingots. Additional introduction of Cr₂O₃ into the charge is necessary for the formation of W carbides in the nickel aluminide matrix.

Abstract: The wear resistance and characteristics of the friction surface of metal coatings with nitride-boride alloying are investigated. The object of the study was the steel deposited with flux-cored wire containing 15% chromium, 0.5% boron nitride, 1.25% titanium di-boride and 0,5% zirconium di-boride. It was established that the average value of the relative wear per test was 0.00416 g/m, which is 1.8 times less than that of the coating metal without borides. The average value of linear wear was 0.0122 mm/m, which is 1,9 times less than that of the coating metal without borides. The average value of the friction torque for the entire friction path in 339 m was 20.96 Nm. The coefficient of friction was 0.425. The hardness of such a metal reaches a maximum value of 57 HRC. The micro-hardness of structural objects is for the matrix 617-648 HV, eutectic 764-847 HV and strengthening phases 1128-1247 HV. It is shown that the metal structure is an iron-chromium martensitic matrix with a eutectic component, formed on the basis of boride (Fe, Cr)₂B and high-strength nitride ε-(Fe, Cr)_2-3N, which is an effective obstacle to dislocation slip under conditions of plastic deformation of the surface at wear.

Abstract: It has been calculated that the introduction of nickel-aluminum additives leads to an increase in the heat effect and allows for the development of materials with the desired phase composition. A comparative analysis of the results of design and instrumentation experiments has shown a satisfactory agreement which allows us to speak about the correctness of the developed numerical model as well as the possibility of selecting optimal initial values ​​of the heat energy source as a factor which allows for controlling the reaction of self-propagating high-temperature synthesis and eventually the phase composition of the final product.

Abstract: The article describes the development of a model for controlling self-propagating high-temperature synthesis. The model is based on computation and theoretical analysis of temperature field dynamics for a propagating combustion wave. The work proves the applicability of this model for the synthesis of boron-containing materials implemented at nuclear power plants. The discrepancy of the model amounts to 20 - 25%, and the satisfactory agreement between the calculation and experimental data testifies the validity of the numerical method and allows calculating any two-component SHS systems.

Abstract: Mixing and sintering aluminium and 20% mechanically alloyed Fe/B nanoparticles provokes the formation of intermetallics in the aluminium matrix when following a powder metallurgy route. Materials were sintered in a wide range of temperatures (from 600 to 1100 oC). Previous studies have shown that these materials present neither important dimensional changes during sintering nor significant differences in mechanical properties. However, sintering temperature strongly affects corrosion resistance and hot rolling capability. Low sintering temperature provides nanocomposites with lower corrosion properties and hot rolling capability. In this work the nanocomposites obtained at different temperatures were characterized by X-ray diffraction. This technique allows following the formation of different intermetallics at each temperature, since being non-equilibrium processes, the use of ternary phase diagram of these elements is not possible.

Abstract: An investigation of coatings obtained by cladding of boron carbide on a low-alloyed steel substrate by an electron beam injected into the air atmosphere was carried out. It was shown that hardened layers had a heterogeneous structure formed during rapid cooling. It was established that a volume fraction of iron borides in the surface layer had a considerable impact on mechanical properties of the material studied.

Abstract: Authors have studied the interaction between high-melting compounds from various classes, such as transition-metal carbides, borides, nitrides, and silicides, and covalent-bonded B₄C, SiC, Si₃N₄, AlN etc. (over 160 phase diagrams), ternary B₄C-SiC-Me^dB₂, SiC-TiC-TiB₂ and other eutectics, which is important for optimizing the sintering temperature, material design and prediction of properties of many materials for high temperature applications including wear, aggressive, impact and radiation conditions. A vast identified group of eutectics with number of components n ≥ 2 has reduced eutectic temperature Т_eut. (in some sistems reducing reaches 1200 °C). Noted, that increasing of n suppresses grain growth, which is particularly important for developing nanostructured ceramics via pressureless sintering and for controlling the ceramic's performance. Multiphase ceramics (SiC-TiC-TiB₂, B₄C-SiC-Me^dB₂, B₄C-W₂B₅-Me^dB₂, B₄C-LnB₆-Me^dB₂, etc.) feature improved mechanical parameters and high wear and impact resistance.

Abstract: The consolidation of refractory ceramic powders at relatively milder conditions with respect to conventional methods represents an important target to achieve. Based on results recently reported in the literature, it is possible to state that the combination of the Self-propagating High-temperature Synthesis (SHS) with the Spark Plasma Sintering (SPS) technologies provides a useful contribution in this direction. Specifically, the two-steps processing route consisting in the synthesis of the ceramic powders by SHS and their subsequent densification by SPS is successfully utilized to obtain various dense MB₂-based materials (M= Zr, Hf, Ta). In this regard, an important role is played by the SHS process, particularly for the synthesis of composite powders. Indeed, stronger interfaces are established among the different phases formed in-situ, so that diffusion phenomena are promoted during SPS. Additional benefits are produced by the use of the latter technology, due to the direct passage of the electric current through the powders undergoing sintering and the die containing them.

Abstract: This study utilizes accurate first principle method to conduct a comparative study on he electronic structure of multiple borides. State density of the borides is also summarized. It is found that lanthanum boride has special electronic structure characteristics. Therefore, it is presumed that there is high superconducting transition temperature (Tc) in lanthanum boride. This study is able to provide asignificant theoretical reference for further experimental research.