Mixture Of B4C Research Articles

Low‐temperature curable adhesive for joining SiC/SiC components: Their application in wide range of temperatures

AbstractHerein we report the formulation of phenolic resin–based adhesive to join SiC substrates for a wide range of application temperatures. The formulation consists of phenolic resin as a binder and a mixture of B4C, Al2O3, Y2O3, Si, and SiO2 powders as active filler. The X‐ray diffraction, thermogravimetric analysis, porosity, and scanning electron microscopy analysis were carried out to understand the reactions occurring within this adhesive during its exposure to application temperatures. These results were also used to understand thermal stability and morphological changes that are involved in the formulated adhesive during its application. The shear strength values of lap joints of SiC substrates made with this phenolic adhesive after exposure to temperatures between 200 and 1500°C were studied to evaluate its adhesive capacity. Obtained SiC joints with this adhesive have shown an excellent lap shear strength value of 24 MPa after its cure. These joints were also found to be intact with good shear strength values of more than 5 MPa even after exposure to temperatures ranging from 200 to 1500°C. The results further confirm that the adhesive is potentially viable for joining SiC segments for their application at a wide range of temperatures in oxidative environments.

Towards optimized designs for control rod absorbers with a high-fidelity simulation method implemented in the RMC code

A high-fidelity simulation method of the control rod absorbers is implemented in the Monte Carlo code RMC. For rare-earth absorbers and B4C, detailed calculations and analyses are conducted for neutronics and depletion characteristics. Three kinds of optimized control rod absorbers are proposed with higher reactivity worth and favorable burnup stability. In these new designs, the composite absorbers possess higher reactivity worth and only average 20% loss of reactivity worth at the end of cycle (EOC). The enriched absorbers have better neutron absorbing capacity and more stable radiation resistance, and the loss of reactivity worth of enriched B4C reduces from 90% to only 7.42% at EOC. For mixed absorbers, the best properties are found for the Dy and B4C mixture when the proportion of Dy is about 60%. The coupling of ZrH2 and Hf achieves a better control efficiency, but unfortunately the loss of reactivity worth increases at EOC.

Chemical interaction between uranium dioxide, boron carbide and stainless steel at 1900 °C — Application to a severe accident scenario in sodium cooled fast reactors

For the understanding of severe accidents in sodium cooled fast reactors (SFR), it is necessary to understand two prototypic accident scenarios such as ULOF (Unprotected Loss of Flow Accident) and UTOP (Unprotected Transient OverPower). As the base knowledge, it is also important to understand high temperature chemical interaction among major core materials such as MOx fuel (MOx: mixed oxide of uranium and plutonium), steel cladding and B4C neutron absorber have to be investigated. This study aims at providing experimental data on phase formation and phase-stability at various temperature and pressure conditions. A first series of samples containing a mixture of B4C and steel were prepared to obtain a homogenous metallic solid. In a second step, these metallic samples were mixed and melted with small UO2 pieces by arc melting. Then these samples underwent a heat treatment at 1900 °C for 1 hour. EDS, EBSD and EPMA analyses were performed to identify the phases formed during the solidification. In addition, thermodynamic calculations were performed for the interpretation of the results, revealing that a carbo-reduction reaction occurs: UO2 + 2 C = 2 CO + U. A significant amount of uranium from the fuel is dissolved in the metallic liquid phase, leading to the formation of mixed borides (UM3B2, UMB4, UM4B, M=Fe,Cr,Ni). In comparison with the UO2/steel interaction, the present results show that the presence of B and C in the melt improves the wetting behaviour of the metallic liquid towards UO2.

Microstructure and mechanical behavior of the laser synthesized composites modified by micro/nano scale rare earth oxides

Micro- and nano-scale rare earth oxides (REOs) modified composites were fabricated by laser scanning the preplaced materials, similar to the process in selective laser melting (SLM). To conduct the comparative study on the effect of different REOs, single-layer composites were prepared on Ti-6Al-4V alloy with Ni60A+ 10 wt% B4C mixture as the basic material and different REOs as the additives. Experiments with micro- and nano-scale REOs (Nd2O3, La2O3) demonstrated benefits in refining the microstructure, improving both the micro-hardness and wear property of the composites, amongst which the nano-scale REOs showed better performance. Compared with the composite without REOs addition, the composite modified with 1 wt% nano-La2O3 exhibited the finest microstructure. The mean micro-hardness increased by ~36.0% from 1058 HV0.2 to 1439 HV0.2, and the wear resistance was improved by 38.5% based on the wear volume loss. The better refining effect of the nano-scale REO was mainly attributed to the small particle size, which was more dispersive in the preplaced materials for increased nucleation. This study is not only useful for surface strengthening of titanium alloys, but also provides inspiration for fabricating bulk composite materials with suitable REO additives.

Concentrated solar power used in preparation of Ti – B4C composites

Concentrated solar power was employed to sinter compacts of Ti + 15 vol% B4C powder mixture. The sintering experiments were performed under protective argon atmosphere at different temperatures and sintering time without external pressure. The sintering experiments were done in 40 kW horizontal solar furnace (SF40) at Plataforma Solar de Almeria (PSA), Spain.The in situ sintering behavior of the Ti – B4C mixture is significantly affected by exothermic reaction of titanium with B4C. In the solar furnace the ignition temperature of this reaction was found to be around 1380 °C. Therefore, the exothermic reaction of Ti + B4C makes the controlling of the solar sintering of these composites very difficult.The optimal temperature of solar sintering was found slightly below 1340 °C for 30 min. No significant reduction of porosity was observed: All samples have more or less the same final porosity value as green compacts prior sintering. The prepared composite samples are brittle. Decomposition of boron carbide led to the creation of TiB2, TiC and complex TiBxC1-x phases which were confirmed by microstructural investigations.

Boronizing of AISI 316L Stainless Steel Using Spark Plasma Sintering Technique

Austenitic stainless-steel has been widely used. Although it offers excellent corrosion resistance, processability, and nonmagnetic properties, it is inferior in terms of wear resistance and hardness. Therefore, the purpose of this study is to form iron boride on an austenitic stainless-steel surface using the spark plasma sintering (SPS) method and to evaluate its properties. The SPS method was utilized because the rapid heating involved in the process reduces the processing time. AISI 316L as a sample material was boronized for 3.6 ks at 1073 – 1273 K at applied pressures of 4 MPa and 8 MPa with a powder mixture of B4C and KBF4. The Vickers hardness profile results showed that the hardness of the untreated sample was ~ 200 HV whereas that of the boronized sample was ~ 2300 HV. The wear test profile showed that the wear resistance of the boronized sample was significantly improved. Moreover, according to elemental analyses, boron diffused from the sample surface to 200 μm and 60 μm when the applied pressure was 8 MPa and 4 MPa, respectively. This indicated that boron diffused to a greater depth when the applied pressure was increased.

Al-Ti-B4C materials obtained by high-temperature synthesis and used as a master-alloy for aluminum

The paper presents microstructure, composition, and burning rate of Al alloy produced by high-temperature synthesis (SHS) from powder mixture Al-Ti-B4C with different concentration of Al powder. It has been established that the phase composition of materials obtained at gas-free combustion includes TiB2, Al, and TiC. It is shown that Al content growth powder in initial Al-Ti- B4C mixture from 7.5 to 40 wt.% reduces the burning rate of the powder from 9*10-3to 1.8*10-3m/s. For the system consisting of 60 wt.% of (Ti + B4C) and 40 wt.% of Al there is the increase in the porosity of the compacted initial powder mixture from 30 to 51 and reduction in the burning rate from 1.8 * 10-3to 1 * 10-3m/s. The introduction of 0.2 wt.% of the obtained SHS materials into the melt of pure aluminum causes reduction of the grain size of the resulting alloy from 1200 to 410 μm.

Densification, Microstructure and Mechanical Properties of Reactive Hot-Pressed ZrB<sub>2</sub>-ZrC-Zr Cermets

This study reviews densification behavior, microstructure and mechanical properties of the various composition ZrB2-ZrC0.6-Zr cermets prepared by reactive hot-pressing of Zr + B4C powder mixtures between 1673 K and 2173 K. During reactive sintering, densification consisted of two parts, one resulted from the volume contraction due to the conversion of Zr + B4C mixture into ZrB2 and ZrC0.6, other resulted from the shrinkage due to grain boundary diffusion and grain boundary migration that mostly contributed to the densification. Highly-dense ZrB2-ZrC0.6-Zr cermets were obtained for Zr + B4C mixtures at equal to or greater than 1673 K. The resulting ZrB2-ZrC0.6-Zr cermets consisted of platelet-like ZrB2 grains, equiaxed ZrC0.6 grains and intergranular Zr. The ZrB2 and ZrC0.6 grains were coarsened with increase of the excess Zr amount and/or sintering temperature. On the other hand, the flexural strength and fracture toughness of the cermets strongly depended on the excess Zr amount and/or sintering temperature. In addition, the crack propagation behavior of the cermets was associated with the excess Zr amount. The cracks directly propagated in the samples with less than 16 vol% Zr, however, the multiple cracking behavior was observed for the samples with equal to or greater than 16 vol% Zr.

ChemInform Abstract: Enhanced Cyclability of Rechargeable Li—O2 Batteries Enabled by Boron Carbide.

AbstractA Li—O2 battery with a B4C based electrode is prepared by casting a 80:20 mixture of B4C and PVDF onto a C paper disk in a 2032 coin cell arrangement with Li foil as anode and 1M LiN(Tf)2‐containing electrolyte.

DRY SLIDING WEAR BEHAVIOR OF HYBRID METAL MATRIX COMPOSITES

In the present study, the Al2219, Al2219/ B4C & Al2219/B4C/MoS2 hybrid composites are investigated under dry sliding wear test as for ASTM G 99-95 standard. Al 2219 base matrix reinforced with B4C & mixture of B4C and MoS2 are fabricated using stir casting technique. By using pin on disc apparatus the test was conducted by taking parameters like sliding distance, sliding velocity and loads. The result reveals that the addition of B4C slightly reduces wear rate of composites, further B4C and MoS2 reinforcement decreases the wear rate of the hybrid composites and increases the wear resistance of the composites. The wear rate decreases with increasing the % of MoS2. At a lower sliding velocity the wear rate decreases and as the sliding velocity increases the wear rate increases. As the sliding distances and load increases the wear rate drastically increases.

Reactive hot-pressing of platelet-like ZrB2–ZrC–Zr cermets: Processing and microstructure

In this study, two methods of powder reactions and reactive hot-pressing were used for the reaction of Zr+B4C powder mixtures. The powder reactions were performed at various temperatures, between 600°C and 1100°C, to examine the reaction behaviour occurring during the synthesis. To fabricate a cermet composed of platelet-like ZrB2 grains and equiaxed ZrCx grains, with intergranular Zr phase, reactive hot-pressing was conduced within temperature range of 1100–1900°C. The effects of temperature on the reactions, densification behaviour and microstructure of the samples were assessed. For samples sintered at 900°C or above, the Zr+B4C mixture was converted into ZrB2 and ZrCx; the conversion was completed at ~1100°C. Densification resulted from volume contraction due to the conversion of Zr+B4C mixture into ZrB2 and ZrCx, and the shrinkage due to grain boundary diffusion and grain boundary migration. For Zr+B4C mixtures sintered at or above 1400°C, relative densities exceeding 97% were obtained. When sintered at or below 1400°C, the resulting ZrB2–ZrCx–Zr cermet consisted of rod-like ZrB2 grains, equiaxed ZrCx grains and residual Zr. Highly-developed platelet-like ZrB2–ZrCx–Zr cermet was obtained only at sintering temperature of 1600°C or greater.

Multifunctional Erosion-Resistant Gas-Diffusion Coatings on Steels

Multicomponent coatings on 20 and Kh18N10T steels formed by the method of vacuum activated diffusion saturation are studied. A mixture of B4C, Al, Ni, Si, Cr, and C powders is used as the saturating medium. A thermodynamic analysis of reactions that accompany the titanizing process. Metallographic, micro-hardness, and X-ray diffraction data are discussed. The cavitation–erosion resistance of multicomponent coatings on steels is studied. It is established that these coatings improve the resistance of steel 20; the destruction rate being the same for both 20 and Kh18N10T steels.

Joining of C/SiC composites by spark plasma sintering technique

CVD–SiC coated C/SiC composites (C/SiC) were joined by spark plasma sintering (SPS) by direct bonding with and without the aid of joining materials. A calcia-alumina based glass–ceramic (CA), a SiC + 5 wt% B4C mixture and pure Ti foils were used as joining materials in the non-direct bonding processes. Morphological and compositional analyses were performed on each joined sample. The shear strength of joined C/SiC was measured by a single lap test and found comparable to that of C/SiC.

Fabrication of Multiple Ceramic Particle Reinforced Iron Matrix Coating by Laser Cladding

Multiple ceramic particle reinforced iron matrix coatings were produced by laser beam melting mixture of B4C, TiO2, Al, and Fe-based self-melting powders. The results showed that the coating were mainly composed of α-Fe, TiB2, and TiC. TiB2 grains showed rectangle structures with deep grey, and that TiC grains exhibited near-cubic morphologies with light grey in the coating. The amount, type, and size of the reinforcements were influenced by the content of B4C, TiO2, and Al. Compared to the substrate, wear resistance of the composite coatings were significantly improved. Furthermore, the coatings possessed more effective protection for scratching and plastic deformation.

Effect of New Superhard Phases Formation on Properties of Composite Processed by SHS

A composite was produced from initial powder mixture of B4C (70 wt.%) and Al (30 wt. %) with WC-Co additives introduced during ball-milling and acting as catalysts by self-propagating high-temperature synthesis and followed by heat treatment of raw samples under gaseous nitrogen flow at 650, 800, 1000, 1150 and 1450 °C, respectively. Formation of different new superhard phases was detected via XRD investigation and analysis of microstructures. Micromechanical properties were tested by nanoindentation. The tribological behavior in dry sliding conditions of the composite was investigated using the ball-on-disk technique against alumina balls. The friction coefficient of the composite increased and wear rate decreased with formation of c-BC2N, c-BN, B13C2, W2B5, Al3BC, AlN, etc. contents during heat treatment at increased temperatures.

Borosiliciding of Fe–Ni alloys and evaluation of their resistance to abrasive wear

X-ray diffraction analysis, Mossbauer measurements and metallographic observations were performed on borosilicide coatings grown at 850°C on Armco iron and the Fe64Ni36 binary alloy using a KBF4-activated powder mixture of B4C and Si3N4. The phase composition of the coatings was determined, a result allowing to show that the thermochemical treatment gives rise to iron boriding and iron siliciding reactions of different strength, depending on the treated material. The presence of Ni in the base metal allows iron-free nickel silicides to form as important components of the coating. The resistance of borosilicide coatings to abrasive wear is evaluated and discussed.

Improvement in mechanical properties and high temperature oxidation resistance of j'TiAl intermetallic cOmpounds by boronising

Intermetallic compounds of λ-TiAl were boronised in the temperature ranges 1150 to 1250°C and 900 to 1050°C with B4C powders and with powder mixtures of B4C and Na2B4O7 respectively. For specimens boronised with B4C powders, substantial porosity was observed at the interface between the coating layer and substrate. The surface hardness of these specimens was ∼ 670 HV and was relatively insensitive to the boronising temperature and time. Boronising TiAl with B4C powders improved both wear and high temperature oxidation resistance. Treatment with a powder mixture of B4C and Na2B4O7 resulted in higher quality coating layers on the TiAl substrate. The highest hardness (∼ 2720 HV) was obtained by a treatment at 900°C for 11 h. The wear and high temperature oxidation resistance of TiAl was more significantly improved than by boronising solely with B4C.

Hardening of steel by alloying in a relativistic electron beam

The possibility was demonstrated of hardening a steel surface layer by alloying it using the energy of relativistic electrons. Investigations were made of how the structure, hardness, and depth of the hardened layer depend on the processing regime and on the initial temperature of the steel in the case of alloying with boron carbide and with Cr+C and Cr+B4C mixtures. The greatest hardening was achieved by alloying with a mixture of Cr and B4C powders. This was due to a higher volume fraction of the second phase in the layer and to the precipitation of chromium carboborides. Several types of alloying utilizing Cr+B4C and containing additional agents and modifiers were developed on the basis of the data obtained.