Boron Carbide B4C Research Articles

Neutron attenuation in some polymer composite material

The scientific paper presents studies of the radiation-protective features of a polymer composite material for protection against space radiation based on poly-tetra-fluoro-ethylene, Bi2O3 bismuth oxide, WC tungsten carbide, B4C boron carbide, TiH1.7 titanium hydride shot. The composite provides for a high degree of protection against ionizing radiation, including protection against exposure to secondary neutrons: macroscopic fast neutrons removal cross-section (E > 2 MeV) 0.1331–0.1414 cm−1, thermal-velocity neutrons removal cross-section (E < 0.4 eV), cm−1 0.1183–0.1257 cm−1. A shield made of the tailored composition of the proposed 6 cm thick polymer composite attenuates the intensity of neutron radiation by more than 50 % at energies from 0.1 to 5 MeV, in particular, the greatest attenuation of the neutron radiation intensity occurs at an energy of 0.1 MeV with a sharp increase in attenuation when passing through a 2 cm thick shield and complete absorption occurs passing through a 6 cm thick shield. This material can be used to protect astronauts and radio-electronic equipment from the effects of adverse or harmful space factors, including exposure to secondary neutrons, and this material can also be used to protect crews of ships with mobile nuclear reactors such as atomic submarines and nuclear-powered icebreakers.

Obtaining Boron Carbide and Nitride Matrix Nanocomposites for Neutron-Shielding and Therapy Applications

The very high capture cross-section of (epi)thermal neutrons by the boron isotope 10B makes elemental boron and its compounds and composites prospective for serving as materials intensively interacting with neutron irradiation. In their nanostructured form, boron-rich materials reveal properties that improve their radiation-performance characteristics. In this regard, new technologies have been proposed for the synthesis of nanocomposites with matrices of boron carbide B4C and hexagonal boron nitride h-BN. For the first time, boron carbide-tungsten and hexagonal boron nitride–(iron,magnetite) composites were obtained, respectively, in the form of layered/sandwich structures of components B4C and W and h-BN nanopowders coated/intercalated with magnetic nanoclusters of iron Fe or magnetite Fe3O4. Studying of their chemical/phase composition, structure/morphology, and some other properties leads to the conclusion that the developed B4C–W and h-BN–(Fe,Fe3O4) composites would be useful for solving important problems of boron-based neutron shielding and BNCT (Boron Neutron Capture Therapy), such as attenuating the gamma-radiation accompanying the absorption of neutrons by 10B nuclei and targeted delivery of 10B nuclei, as BNCT therapeutic agents, to tumor tissues using control by an external magnetic field, respectively.

Effect of cobalt additive on phases formation in boron carbide matrix composites B4C–(Ti,Zr)B2–W2B5

The proposed method of obtaining of boron carbide B4C matrix composites B4C–(Ti,Zr)B2–W2B5 without and with cobalt Co additive is based on preparing corresponding precursor pastes from commercially available compounds and their processing in controlled thermal regimes. This technique makes it possible to synthesize all the component phases – B4C, TiB2, ZrB2, W2B5 and Co – from cobalt-containing liquid-charge at relatively low temperatures of ∼1000 °C, while from cobalt-free precursors only zirconium diboride formation can be observed under the same conditions. Maintaining the initial grains size or their growth inhibition at spark-plasma sintering of boron carbide matrix composite powders with cobalt additive is one more advantage of the introduced approach.

ОБРАБОТКА РЕЗУЛЬТАТОВ ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ ИСПОЛЬЗОВАНИЯ ТЕХНОЛОГИЙ КОМПЛЕКСНОГО МИКРОПЛАЗМЕННОГО УПРОЧНЕНИЯ РАБОЧИХ ОРГАНОВ И ДЕТАЛЕЙ СЕЛЬСКОХОЗЯЙСТВЕННЫХ МАШИН

Today, the problem of maintaining the efficiency of complex modern domestic and foreign agricultural machines is quite acute. The working units of agricultural tillage machines operate in an aggressive abrasive environment, which leads to their intensive wear and, as a result, to the loss of geometric shape. This, in turn, leads to a violation of agrotechnical requirements, which significantly affects the yield of cultivated crops. Serial working units of soil-cultivating machines are made of alloy steels of the ST65G type with a working hardness of HRC 55 ... 60. The purpose of the research is to increase the wear resistance of the working bodies of tillage agricultural machines by using the technology of complex microplasma hardening, with the development of a methodology for determining rational modes of processing working surfaces. To evaluate the effectiveness of complex hardening of laboratory samples, studies of the elemental composition of the hardened layer were carried out. Plates made of ST65G steel were used as laboratory samples. Hardening was carried out using various combinations of cermet powders and microplasma hardening modes. Determination of wear resistance was carried out on a friction machine 77 MT-1. The best results were noted after vibro-arc hardening followed by electrospark alloying and the use of a cermet powder consisting of 80% PG-10N-01 matrix powder and 20% B4C boron carbide. Based on the indicators of hardening regimes, Lagrange interpolation polynomials were constructed, which describe the dependence of the amount of sample wear on the current and voltage, an algorithm was developed for determining rational hardening regimes to achieve maximum wear resistance of the studied samples. The microhardness of the surface of products during electrospark hardening increased up to 2 times, and with vibroarc in combination with electrospark alloying and the use of special pastes with cermet powders - more than 3 times. The depth of the hardened surface layer with complex hardening is about 0.3 mm.

Analysis of sintering process of Alumix431-B4C composites

This paper presents the results of a study on the sintering process of composites made of a mixture of Alumix 431 powders with B4C boron carbide. Sintering was carried out at the following temperatures: 550, 580 and 600 ℃. The process of sintering Alumix powders is a very complex issue due to the possibility of many types of mutual reactions of the elements constituting its components and their interaction with boron carbide. The study included the preparation of green compacts from a mixture of powders with the addition of 5 wt % B4C and sintering in a NETZSCH 402ES/3 differential dilatometer; the density and microstructure of the sinters were examined using scanning microscopy and X-ray phase analysis. Analysis of the dilatometric curves allowed the sequence of the emerging liquid phases and their impact on the course of dimensional changes as well as the microstructure of the finished composites to be determined, indicating the importance of the reaction of the aluminium matrix with magnesium, copper and zinc. It was also indicated that the B4C boron carbide addition may decompose, resulting in the appearance of B12Mg and Al4C3 phases. The research also showed that the addition of carbide did not adversely affect the density of the sinters as composites with a density exceeding 95 % of the theoretical density were obtained.

Investigating the possibility of extending the BWR cycle length for 15 years of operation by mixing highly enriched UO2 fuel with burnable absorbers

This paper investigates the possibility to extend the cycle length of boiling water reactor bundles to 15 years of operation with three different burnable poisons; gadolinium, erbium, and boron carbide. This can be carried out by mixing highly enriched UO2 fuel (15–19.9% U-235) with high concentrations of Gadolinium oxide (3–14% Gd2O3) or Erbium oxide (2–4% Er2O3).The boron carbide B4C was modeled as (Al2O3-B4C) rods in the bundle guide tubes. MCNPX code 2.7 was used to evaluate infinite multiplication factor (K-inf), power distribution, peaking factor, void reactivity coefficient, fuel cycle length, depletion of U-235, and fissile inventory ratio for the three designs at 40% void. The MCNPX simulation showed that introducing gadolinium rods at the bundle periphery has the advantage of lowering reactivity swing throughout the exposure range. The uniform distribution of erbium in all fuel rods contributed to the flattening of peaking factor at all the burnup stages. For the B4C design, the author found that the assembly with B4C–Al performs best in terms of reactivity flattening when five of the B4C–AL2O3 rods are positioned in the central region of the assembly. Furthermore, the fuel temperature coefficient is more negative for gadolinium design at all burnup stages. On the other hand, the boron model delivers the lowest control rod worth. Finally, the moderator temperature coefficient is more negative for erbium and WABA designs due to the enhanced thermal neutrons capture by the effect of the strategic arrangement of WABA rods and the uniform distribution of erbium.

Micromechanical properties and transverse rupture strength of a Cu-Ti-C-B composite

The paper presents the results of studying the microstructure, chemical and phase compositions of a Cu-Ti-C-B composite produced by self-propagating high-temperature synthesis (SHS). It has been found that the matrix of the composite is a titanium-doped copper-based solid solution. Titanium carbide TiC and titanium diboride TiB2 are the strengthening phases. Single particles of boron carbide B4C unreacted in SHS have been detected, with the hardness 3332 HV 0.1. The composite density is 6.8 g/cm3. The overall hardness of the composite is 60 to 62 HRC. The uneven distribution of the constituents in the volume of the composite causes the uneven distribution of its micromechanical properties. The most ductile constituent of the composite is the Cu+TiC mechanical mixture, which ensures the high ductile fracture energy of the composite in transverse bending testing. On the fracture surface, at the interface separating the B4C particles and the copper-based solid solution, there are microvoids indicating the start of microcracks growth. The strength of the composite is Rbm30 = 820 MPa.

Структура и микромеханические свойства СВС-композитов с медной матрицей: особенности формирования

Self-propagating high-temperature synthesis (SHS) is one of the promising methods for producing strong and wear-resistant composites. The use of copper as a matrix due to the unique combination of electrical and thermal conductivity is of particular interest. Monolithic SHS composites of the Cu–Ti–C–B and Cu–Ti–C systems are currently little studied. The information on the phase composition of such composites is contradictory, and data on micromechanical properties is practically absent. The paper presents the results of a comparative analysis of the structure and micromechanical properties of composites of the Cu–Ti–C and Cu–Ti–C–B systems. It is found that the matrix of both composites is a copper-based solid solution supersaturated with titanium, in which nanosized Cu4Ti intermetallic compound particles precipitate upon cooling. TiC particles (Cu–Ti–C composite) and TiC and TiB2 particles (Cu–Ti–C–B composite) are the strengthening phases resulting from SHS. In the Cu–Ti–C–B composite, the original particles of unreacted B4C boron carbide were preserved, the microhardness of which was 3680 HV 0.1. The most ductile structural constituent in the Cu–Ti–B system composite is the Cu+Cu4Ti mechanical mixture, due to which further plastic deformation is possible to obtain parts of a given shape. During the study of micromechanical properties, the maximum strength indicators of HIT, HV, We, Re, HIT/E* were recorded in the Cu–Ti–C–B system composite, which allows expecting high wear resistance of products made of it.

Economic feasibility of using the technology of carbon-vibro-arc hardening for hardening the pointed paws of tillage machinery

The article describes the rational technology of carbo-vibro-arc hardening (CVAH) developed by the authors using a multicomponent paste of the working surfaces of the pointed paw of tillage machinery. An economic assessment of the feasibility of using CVAH for strengthening pointed paws was carried out. PG-FBKh6-2 powder was used for research as the basis of a multicomponent paste for CVAH. The boron carbide B4C served as a ceramic component of the paste, the mass content of cryolite was 10 %. CVAH was carried out on a VDGU-2 installation. A carbon electrode of 8 mm in diameter was used to form reinforcing composite coatings.&#x0D; The implementation of developed technology involves firstly the cleaning of working part of the paw. Then a multicomponent paste is prepared, it is applied to the surfaces, hardened and dried until cured. After it the CVAH is done with the formation of a composite coating and the resulting coating is monitored. The rational composition of the multicomponent paste according to the results of a set of studies should be as follows: PG-FBH6-2 powder 60 % by weight, B4C 30 % by weight, cryolite the rest. Rational CVAH modes: current strength 70 ... 80 A, carbon electrode vibration frequency 25 Hz, electrode vibration amplitude 1,1 mm. The thickness of the formed reinforcing composite coating is 0,91,0 mm, and its hardness is 7072 HRC. The developed technology, due to low additional capital investments, can be used both in small workshops of farms and in the conditions of specialized repair and restoration enterprises. The calculation of the economic efficiency of the developed technology for strengthening pointed paws showed that the expected annual economic effect from the introduction of the technology will be 120, 191 rubles with the hardening of 430 blades of KShU-12N cultivators. Thus, the developed technology is economically feasible and can be recommended for implementation in production.

Modeling of shock-wave loading of carbides as mixtures of components

The results of numerical experiments on the modeling of shock wave loading of solid and porous carbides with various stoichiometric compositions are presented. The model is based on the assumption that all the components of the mixture, including gas, have similar pressure, velocity and temperature. The model allows describing the behavior of porous materials and mixes in a wide range of porosity and pressures with precision of experiment. The behavior of complex materials such as carbides is considered as a mixture. The model accurately describes the behavior of the carbides with equal shares of the components of WC, TiC, TaC, NbC and the behavior of boron carbide B4C. Comparison for data of calculation and experimental data was held for carbides with different porosity.

On Modeling of Synthesis Process of Boron Carbide Based Nanocomposites

Nanocomposites based on boron carbide B4C are hard materials with wide field of applications in modern technologies. A system of first-order ordinary differential equations that simulates the process of chemical synthesis of nanopowders of B4C–TiB2 compositions containing titanium diboride (TiB2) as an additional phase is suggested and resolved numerically for a typical ratio of reaction constants. Reagents and products concentrations are found as time-functions. In this way, the optimal route of production technology of boron carbide-based nanomaterials can be identified.

ВЛИЯНИЕ ДОБАВКИ КАРБИДА БОРА НА СТРУКТУРУ И ТВЕРДОСТЬ НИКЕЛЕВОГО ПОКРЫТИЯ

Laser cladding is increasingly frequently used in various branches of mechanical engineering since it has such advantages over traditional methods of depositing coatings as high heating and cooling rates and minimal mixing of base and melting materials. Laser-clad coatings are usually characterized by a fine-grained structure and a minimal heat-affected zone. Coatings formed from the Ni–Cr–B–Si powders are also very common in industrial applications, as they have good resistance to wear, corrosion, erosion, etc. Various strengthening particles can be added to this group of powders to improve the properties of the deposited coating. Boron carbides can act as such particles since they have high hardness, thermodynamic stability, and wear resistance. In this regard, the paper investigated the influence of the 7 wt. % of boron carbide B4C addition on the structure and hardness of the NiCrBSi coating formed by laser cladding of PG-SR2 powder on the surface of 30HRA steel. Using the scanning electron microscope, the authors carried out microscopic studies of the structure of NiCrBSi and NiCrBSi–B4C coatings and presented the results of X-ray spectral microanalysis. The study shows that the structures of both coatings in the deposited state are characterized by uniformity and fine-grain structure. The investigation revealed that the samples with NiCrBSi and NiCrBSi–B4C coatings have a narrow transition zone from the deposit to the base metal. The paper presents the results of measuring the microhardness of coatings indicating a decrease in the microhardness of laser-clad nickel-based coatings with the boron carbide addition.

Numerical simulation of deformation and fracture of metal-matrix composites with considering residual stresses

Thermomechanical behavior of metal-matrix composite materials is investigated. Boron carbide B4C and high-strength aluminum alloy 6061-T6 are used as strengthening particle and matrix materials, respectively. Microstructure of the metal-matrix composite takes into account the complex shape of particles explicitly. Isotropic elastoplastic and elastic-brittle models were used to simulate the mechanical response of the aluminum matrix and ceramic particles, respectively. To investigate the crack initiation and propagation in ceramic particles, a Huber type fracture criterion was chosen that takes into account the type of the local stress state in ceramic materials: bulk tension or compression. The composite material with a single particle of both the really observed in the experiment and ideally round shapes is considered. The influence of the residual thermal stresses arising during cooling of the composite material from the temperature of aluminum recrystallization to the room temperature on the character of plastic strain localization in the aluminum matrix and fracture of carbide particles and on the macroscopic strength of the composite under external tension or compression is studied numerically. Two-dimensional dynamic boundary value problems in the plane-stress and plane-strain formulations were solved numerically by the finite element method using the Explicit module of the Abaqus software package. VUMAT subroutine procedures incorporating the constitutive models were developed and integrated into the Abaqus solver. Based on the results of the numerical simulation, it was concluded that the residual thermal stresses arising during cooling lead to the change in the mechanism of the particle fracture from in-particle cracking to debonding and increase the strength of the composite subjected to tension after the cooling.

The effect of boron carbide on the mechanical properties of bidirectional carbon fiber/epoxy composites

This research work based on carbon fiber epoxy (CF/Ep) composites shows the effect of Boron carbide B4C filler on mechanical properties using a hand layup procedure followed by the vacuum bagging process method. The boron carbide fillers were uniformly dispersed in epoxy resin and used as matrix material. The weight percentage of (B4C) filler material in the composite was varied and mechanical properties were obtained with microfiller. The T800CF/Ep composites with 1%wt., 3%wt. and 5%wt. B4C fillers were taken for evaluating the mechanical properties. All composites were fabricated with an equal weight percentage of carbon fiber and a similar consolidation process. The mechanical properties like tensile properties, flexural properties, Interlaminar shear strength, impact strength and hardness are studied to know how the mechanical response of composite structures varies with filler addition. Testing followed the trend of 1%wt. > 3%wt. > 5%wt. of B4C in all mechanical properties of B4C filled CF/Ep composites. Tensile strength of 1%wt. B4C filled composites were better than basic CF/Ep composites whereas 3%wt. & 5%wt. B4C filled composite values were lower. The tensile modulus of all the B4C filled composites was better than basic CF/Ep composites. Flexural properties of 1%wt. and 3%wt. B4C filled composites were better than basic CF/Ep composites whereas 5%wt. B4C filled composite values were lower. Interlaminar shear strength (ILSS) of 1%wt. B4C composites gave better results whereas 3%wt. and 5%wt. B4C filled composites gave lower results. The impact energy of all composites gave lower values than basic CF/Ep composites. Hardness values of all B4C filled composites were better than basic CF/Ep composites. The most important developments in the mechanical properties of composites are further supported by scanning electron microscopy.

Microwave synthesis of B4C nanopowder for subsequent spark plasma sintering

Utilization of microwave-assisted (MW) synthesis and subsequent spark plasma sintering as an efficient and rapid synthetic route toward the preparation and consolidation of ultrahard B4C boron carbide without additives is reported. Magnesium dodecaboride (MgB12) and carbon were used as raw materials for stepwise MW synthesis of B4C at irradiation power of 900W. The comprehensive analytical studies showed that after few minutes of microwave irradiation of reactive mixture single phase nanoparticles of boron carbide (40–50nm) covered by carbon nanolayer are formed. Optimum sintering parameters for the powder compaction were revealed and dense specimens (>99%) with hardness of around 35GPa and substantially improved fracture toughness of 5.7MPam1/2 were produced from nanosized B4C powder without any additives. Erosive wear behaviour of B4C against silica particles impact studied at room temperature demonstrated a high erosion resistance for the fully dense compacts sintered at 1900°C.

Circular economy practice: From industrial metal waste to production of high wear resistant coatings

Recently, recycling has become an essential issue in the industrial sector due to the soared consumption of materials and energy. One of the few possible ways to recycle metal waste is re-melting and converting the waste to new products. However, it requires a lot of energy, causes environmental contamination and is not applicable worldwide. Landfilling is no longer an option. This research paper focuses on finding an alternative way to recycle industrial waste by using the Submerged Arc Welding method (SAW) and metal waste, what is collected by manufacturing companies, in order to produce wear resistant hard-facings. When selecting metal waste, the greatest attention was given to waste of alloys with carbide forming elements. Turnings, shavings, and chips, as well as debris of high speed tool steel (HS6-5-2), ledeburitic high chromium cold work steel (X210Cr12), cast iron chips, waste of boron carbide B4C, worn grinding wheels (SiC), sintered hardmetal (H123, HG30) all were chosen as the remedy for reinforcement. Five possible compositions of above mentioned waste were discussed and tested on wear. SAW technique with properly chosen parameters: current 180–200 A, voltage 22–24 V, travel speed – 14.4 m/h was adapted for the production of hard-facings. Two methods to introduce waste metal powder to the weld zone were utilized: spreading of powder over the surface of substrate, and mixing with standard flux. Hard-facings obtained from waste materials were tested on abrasive emery wear. Volume-wear loss in most cases was compared to commercial steel grades. Wear results confirmed expectations as wear resistance of waste based hardfacings ∼2 times exceeded the wear resistance of commercial alloys.

Investigation of the microstructure of diffusion coatings of carbon steel obtained by simultaneous diffusion saturation with boron, chromium and titanium

The mechanism of boron diffusion under conditions of simultaneous saturation of steels with boron, chromium and titanium are poorly represented in the literature. It is noted that exactly three-component saturation with boron, chromium and titanium allows to obtain diffusion coatings with unique properties. The microhardness of such coatings can achieve 5000 HV, which corresponds to the microhardness of boron carbide B4C. In addition, such coatings, depending on the saturation parameters and the saturable material, can also show high durability values. The microstructure of the diffusion coatings on carbon steels Grade C and steel 1045 has been studied. It has been shown that during the simultaneous diffusion of boron, chromium and titanium under the boride layer additional perlite volumes are formed. The perlite that existed in the steel before the diffusion processes, as a result of diffusion, is fragmented.

Определение энергии и флюенсов протонов, коллективно ускоренных в ускорителе с диодом Люса

Plates of boron carbide B4C were used as refractory targets for determination of energy and fluencies of protons collectively accelerated in a Luce diode accelerator by control of 7Be and 13N gamma-radioactivities induced by nuclear reactions 10B(p,α)7Be and 12C(p,γ)13N, respectively. The Luce diode exploited a cylindrical tungsten rod as a cathode and polyethylene washer as an anode, producing pulsed electron beams with durations and currents of up to 100 ns and 30 kA at voltages of 250 kV. The technique allows controlling proton energies within the range of 500-1500 keV and fluencies of up to 5•1013 protons per cm2 per pulse.

Helium cluster nucleation and growth in implanted B4C boron carbide

When B4C boron carbide is irradiated in neutron reactors, high quantities of helium are produced due to the 10B(n,α)7Li neutron absorption reactions. It is well known that most helium remains in the material, this inducing swelling and cracking. However very few studies deal with the nucleation and growth of the helium clusters. In this paper, B4C is implanted with helium and its behaviour is studied mainly thanks to TEM observations. Different parameters are considered: helium concentration, implantation temperature, post-implantation annealing temperature, width of the implanted zone and overlap with ballistic damage simulating the fast neutron scattering. We observe that helium clusters form either on structural defects (grain and twin boundaries, precipitates) or thanks to irradiation damage induced nucleation. When implanted at low temperature and then annealed, nanometric bubbles form that eventually agglomerate as flat discs associated with strong strain fields. In the temperature range encountered in fast neutron reactors, those discs evolve toward parallel 20–50 nm diameter helium platelets. Grain boundaries are very efficient trapping sites, no evolution of the intergranular helium bubbles is observed up to 1200 °C. In the implanted zone, the platelets change into polyhedron bubbles over 1100 °C with a relaxation of the strain fields together with a strong density decrease. The addition of a ballistic damage increases the density of the helium bubble germs.

Boron carbide B4C ceramics with enhanced physico-mechanical properties sintered from multimodal powder of plasma dynamic synthesis

Boron carbide B4C as one of the hardest materials known is of a great scientific interest for years due to a unique combination of different useful properties. The ceramics on its basis has many prospective applications. However, the widespread usage of this ceramics is limited due to the relatively low fracture toughness as well as the poor sinterability. This work shows the possibility to obtain the ceramics with enhanced physico-mechanical properties based on the powdered boron carbide B4C prepared by a plasma dynamic method. The key features of this powdered material are a single-crystalline particle structure and their multimodal distribution from several nanometers to several micrometers that is confirmed by the results of both scanning and transmission electron microscopy. Sintering the ceramics based on the as-prepared B4C powder by SPS technology at the temperature of 1950 °C, pressure of 60 MPa and time exposure of 5 min allows not only achieving the expected values of ceramics density (~99% relative to the theoretical one) but also the high hardness (~37 GPa) and fracture toughness (6.7 ± 0.3 MPa·m1/2).