Boron Carbide Layer Research Articles

Enhancing interfacial heat conduction in diamond-reinforced copper composites with boron carbide interlayers for thermal management

In this work, we have synthesized a copper/boron carbide/diamond composite structure via magnetron sputtering. Surface roughness of the diamond layers was characterized using atomic force microscopy (AFM), and interfacial thermal conductance (ITC) between copper and diamond was experimentally measured by the Time-domain Thmoreflectance (TDTR) technique. Molecular dynamics (MD) simulations were conducted to investigate the influence of the <010> crystal plane thickness of boron carbide and interface roughness on the ITC. The results indicate a significant increase in ITC with the incorporation of a <010>-oriented boron carbide interlayer. The ITC initially rose and then fell as the boron carbide layer thickness increased, reaching a maximum of 286.52 MW m−2 K−1 for a three-layer (approximately 2 nm) interlayer, which is 14.1 times higher than that of the unmodified interface. Additionally, by creating a three-dimensional sinusoidal rough interface, we observed that increasing interface roughness can further enhance heat transfer efficiency up to a certain threshold, beyond which a saturation in phonon heat conduction is anticipated. The simulation outcomes are in good agreement with the experimental data, confirming the reliability of our findings.

Polarity Effect on the Heteroepitaxial Growth of B&lt;sub&gt;x&lt;/sub&gt;C on 4H-SiC by CVD

The chemical vapor deposition (CVD) growth of boron carbide (BxC) layers on 4H-SiC, 4°off substrates was studied. Depending on the polarity of the substrate, different results were obtained. On Si face, the direct CVD growth at 1600°C under a mixture of BCl3+C3H8 systematically led to polycrystalline BxC films, whatever the C/B ratio in the gas phase. On the C face, heteroepitaxial growth was obtained for C/B ratios = 12 or higher with a step bunched morphology. If a boridation step (10 min at 1200°C under BCl3 flow) was used before the CVD growth, then heteroepitaxy was successful on both substrate polarities. To explain these results, a mechanism is proposed which involves the nature of the chemical bonds at the early stage of nucleation. It is suggested that a full B coverage of the SiC surface should favor the nucleation of the B-rich (0001) plane of BxC, promoting thus the heteroepitaxial growth along this direction.

An investigation of the ballistic impact behavior of multi-layered armor structure

In this research, a multi-layered composite armor was introduced by combining ceramics, fiber-reinforced composite and metal alloy with the aim of making the armor capable of resisting ballistic impact. A model was developed in ABAQUS/Explicit to predict the impact performance of armor in different scenarios. A thinner version of the proposed structure was manufactured, and experiments were conducted. Data were collected and analyzed including initial and residual velocity and absorbed kinetic energy. The experiments and simulations showed similarities in how the materials response to the ballistic impact. It was found that the thickness of each component contributes to the total ballistic resistance of the whole structure. By putting 20 mm thick Boron carbide layer in front layer, armor structure can absorb more kinetic energy than having 10 mm thick Boron carbide front layer. The sequence order of layers also affected the protection of armor structure. If the front layer is Kevlar/epoxy, armor structure cannot withstand multi-hit attacks because of significant delamination in these layers. Also, the Boron carbide core that had Kevlar/epoxy layer in the front was more shattered than the Boron carbide front layer that had Kevlar/epoxy as the core layer. By applying cohesive layers between Kevlar/epoxy layers, the displacement of fibers in the bonded composite layers was equal to 68% of the displacement of fibers in the unbonded Kevlar/epoxy layers. Also, the multi-layer structure with bonded Kevlar/epoxy layers exerted more stress on projectile after impact compared to structure with unbonded Kevlar/epoxy layers.

Impact of fiber surface gas treatments on interfacial bonding in SiC/BN/SiC minicomposites

AbstractBN interphases with different microstructures and a structural gradient were prepared by chemical vapor deposition (CVD) within SiC/SiC minicomposites. The interfacial shear stress (ISS) measured by the fiber push‐out test and the debonding location in the fiber/matrix interface zone during mechanical loading depends on the BN interphase structure. The ISS is higher when the structural organization of the BN interphase is poor, in which case debonding occurs on the fiber side. The Hi‐Nicalon S fiber surfaces were gas‐treated to strengthen the bond with the interphase. BCl3‐based reactive CVD treatments have produced a thin boron carbide layer on the fiber surface, resulting in a 30% increase in ISS. However, the minicomposites are brittle in tensile tests due to fiber bridging by parasitic boron clusters. Short‐time CVD of SiC increases the fiber surface roughness and doubles the ISS, but again the minicomposites are brittle, indicating the need to better modulate the resulting roughness and adjust the interphase. Finally, ammonia treatments have nitrided the fiber surface and increased the ISS by 12%. While the increase in interfacial bonding measured at the microscopic scale was small, this nitriding treatment did not embrittle the minicomposites at the macroscopic scale.

Effective Thermal Properties of a HTS Transition Edge Bolometer for High‐Flux Neutron Detection

AbstractMany applications require monitoring of increasingly high neutron flux levels. Pre‐neutron characterization is performed of a superconducting transition edge bolometric device, sensitive to neutrons by an enriched boron carbide (10B4C) layer. Heat from the absorption of neutrons is simulated using an attenuated laser, while the detector is cooled to the critical temperature, Tc. Frequency dependent (4–25 Hz) and constant input power measurements are performed on a 10B4C‐coated and a non‐coated pixel. Results are used to fit a two lumped element thermal model. The effective specific heat is highly dependent on the input pulse duration due to the interconnected stack structure. For modulated pulses, the active volume in the thermal circuit is the full depth of the substrate in the area under the pixel. For constant power input, a large portion of the substrate is heated and the interface conductivities to the cold finger are found to be important. The detectivity is D* = 3.5 × 108 , and is only slightly lower than similar detectors. Understanding the dynamics of the detector better and using neutron excitation, it is expected that optimizations can lead to an equally good detector for cold to thermal neutrons at flux levels &gt;106 n cm−2s−1.

Structural and component characterization of the B4C neutron conversion layer deposited by magnetron sputtering

Neutron conversion detectors that use 10B-enriched boron carbide are feasible alternatives to 3He-based detectors. We prepared boron carbide films at micron-scale thickness using direct-current magnetron sputtering. The structural characteristics of natural B4C films, including density, roughness, crystallization, and purity, were analyzed using grazing incidence X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and scanning electron microscopy. A beam profile test was conducted to verify the practicality of the 10B-enriched B4C neutron conversion layer. A clear profile indicated the high quality of the neutron conversion of the boron carbide layer.

Study of interface reaction in a B4C/Cr mirror at elevated temperature using soft X-ray reflectivity.

Boron carbide is a prominent material for high-brilliance synchrotron optics as it remains stable up to very high temperatures. The present study shows a significant change taking place at 550°C in the buried interface region formed between the Cr adhesive layer and the native oxide layer present on the silicon substrate. An in situ annealing study is carried out at the Indus-1 Reflectivity beamline from room temperature to 550°C (100°C steps). The studied sample is a mirror-like boron carbide thin film of 400 Å thickness deposited with an adhesive layer of 20 Å Cr on a silicon substrate. The corresponding changes in the film structure are recorded using angle-dependent soft X-ray reflectivity measurements carried out in the region of the boron K-edge after each annealing temperature. Analyses performed using the Parratt recursive formalism reveal that the top boron carbide layer remains intact but interface reactions take place in the buried Cr-SiO2 region. After 300°C the Cr layer diffuses towards the substrate. At higher temperatures of 500°C and 550°C the Cr reacts with the native oxide layer and tends to form a low-density compound of chromium oxysilicide (CrSiOx). Depth profiling of Si and Cr distributions obtained from secondary ion mass spectroscopy measurements corroborate the layer model obtained from the soft X-ray reflectivity analyses. Details of the interface reaction taking place near the substrate region of boron carbide/Cr sample are discussed.

Development of hard, anti-reflective coating for mid wave infrared region

In the 3–5 μm Mid Wave Infrared (MWIR) thermal imaging region, the number of alternative transparent optical substrate materials are quite limited. Silicon (Si) and germanium (Ge) are among the common optical materials used in the MWIR region. However, these materials and the thin film coatings on them, suffer from low hardness and brittleness hence need to be protected against scratches and hard flying particles like sand, dust, etc.. In industry, a single layer amorphous Diamond Like Carbon (DLC) coating is used to protect the outer layer while transmitting MWIR energy. This paper suggests single layer Boron Nitride (BN) and Boron Carbide (B4C) coatings as alternatives to commercial DLC coating, providing the necessary protection and transmission efficiency with anti-reflective properties. The proposed boron-contained coatings also have an advantage of greater temperature resistance over DLC. Finally, a two-layer anti-reflective coating containing Boron Carbide layer as an outer protective coating is demonstrated.

Dense KNN Polycrystals Doped by Er2O3 Obtained by Hot Pressing with Hexagonal Boron Nitride Protective Layer.

Analysis of dense Potassium Sodium Niobate (KNN) ceramic obtained by hot pressing (HP) method at 1100 °C are presented in this paper. The synthesis of KNN-based piezoelectrics meets the following challenges—low density of material, uncontrolled K/Na ratio, multiphase composition and formation of different KNN structures. The classical hot pressing approach results in contamination by carbon originating from graphite molds. The proposed hexagonal Boron Carbide (h-BN) layer between green sample and graphite mold could protect samples from carbon contamination. Additionally, the presence of h-BN may decrease the formation of oxygen vacancies, which allows us to maintain the semiconductor features of the KNN structure. Remaining issues were addressed with the addition of excess Na and Er2O3 doping. The results showed that excess Na addition allowed us to compensate evaporation of sodium during the synthesis and sintering. Er2O3 was added as sintering aid to limit abnormal grain growth caused by h–BN addition. The modification of amount of Na and Er2O3 addition resulted in high purity KNN samples with tetragonal structure and apparent density higher than 97%. Finally, piezoelectric features of prepared dense samples were measured and presented.

Interface Study on the Effect of Carbon and Boron Carbide Diffusion Barriers in Sc/Si Multilayer System.

Sc/Si multilayers are one of the promising material combinations commonly used in the spectral range of 35-50 nm. However, diffusion and silicidation at the interfaces of Sc/Si multilayers limit widespread applications of this material combination. To improve the properties of Sc/Si multilayers, the scheme of barrier layers is utilized. In this work, a series of Sc/Si multilayers with boron carbide and carbon barrier layers were designed and fabricated to compare the properties including interface quality and thermal stability. The effect on the multilayer structure and quality before and after annealing were investigated by using grazing-incidence X-ray reflection, X-ray diffraction, rocking-curve X-ray diffuse scattering, transmission electron microscopy, and selected area electron diffraction. The results indicate that severe interdiffusion and crystallization occur in the multilayer with a carbon barrier after annealing. However, a boron carbide barrier layer improves thermal stability up to 550 °C since the interfaces remain abrupt and clear after annealing. The multilayer quality is confirmed to be improved significantly.

Creep in interlaminar shear of an Hi-Nicalon™/SiC–B4C composite at 1300℃ in air and in steam

Creep behavior in interlaminar shear of an advanced SiC/SiC composite with a self-healing matrix was investigated at 1300℃ in laboratory air and in steam. The composite was processed via chemical vapor infiltration (CVI). The composite has a self-healing oxidation-inhibited matrix comprising alternating layers of silicon carbide and boron carbide and is reinforced with laminated woven Hi-Nicalon™ fibers. Fiber preforms were coated with pyrolytic carbon followed by a boron carbon overlay. The interlaminar shear properties were evaluated at 1300℃. The creep behavior was examined for interlaminar shear stresses ranging from 13 to 20 MPa in air and in steam. Primary and secondary creep regimes were observed in all tests conducted in air and in steam. Creep run-out (defined as 100 h at creep stress) was achieved at 13 MPa in air and in steam. Presence of steam had little influence on creep strain rates and creep lifetimes. However, larger creep strains were accumulated in steam than in air. The retained properties of all specimens that achieved creep run-out were characterized. Composite microstructure and damage and failure mechanisms were investigated.

Long-term evolution of spherical shell with boron carbide layer after explosive compression

Predictive simulation of the long-term response of multilayer targets with ceramics layers to shock compression demands appropriate material models. Because ceramics are complex brittle materials, which tend to lose their strength under heavy loads, such simulation requires the failure models well-proven for a wide range of strains and strain rates. Standard plate impact experiments provide the main data utilized for developing and validating the mechanical models of material response to shock compression. However, apart from the fact that such experimental data are inherently one-dimensional, they can be insufficient to verify the failure model at relatively low strain rates typical for long unloading waves. Here, we present the experimental results for explosive compression of a spherical multilayer shell initiated by a single detonator. The explosive-coated shell consists of the nested spherical layers: the outer made of boron carbide and the inner of lead. X-ray images showing the evolution of those layers after detonation are then compared with simulation results. Propagation of the compression wave through the layers resulting in ceramics damage is analyzed in detail. We demonstrate that the failure model of boron carbide should be adjusted for compressions below 10 GPa to achieve a good agreement with our experimental images. Such an improved failure model provides the predictive simulation of long-term dynamics of targets after unloading, and it has almost no effect on wave profiles after plate impact.

Depth-resolved compositional analysis of W/B4C multilayers using resonant soft X-ray reflectivity.

W/B4C multilayers (MLs) consisting of ten layer pairs with varying boron carbide layer thicknesses have been investigated. The ML structures were characterized using grazing-incidence hard X-ray reflectivity (GIXR), resonant soft X-ray reflectivity (RSXR), hard X-ray photoelectron spectroscopy (HAXPES) and X-ray absorption near-edge spectroscopy (XANES). Depth-resolved spectroscopic information on the boron carbide layer in W/B4C MLs was extracted with sub-nanometre resolution using reflectivity performed in the vicinity of the B K-edge. Interestingly, these results show that the composition of boron carbide films is strongly dependent on layer thicknesses. HAXPES measurements suggest that most of the boron is in the chemical state of B4C in the multilayer structures. XANES measurements suggest an increase in boron content and C-B-C bonding with increase in boron carbide layer thickness.

Internal Stresses in Mo/Y Multilayer Mirrors

Mo/Y multilayer mirrors designed to operate in the range of 9–11 nm are considered. The dependence of the internal stress of such mirrors on the molybdenum fraction is studied for the first time. It is shown that structures with zero stress are characterized by a reflection coefficient of about 6%. The experimentally obtained maximum reflection coefficient (30%) corresponds to a stress of –160 MPa. The influence of a buffer layer of boron carbide on the internal stress and reflectance factor of the Mo/Y mirrors is investigated. A Cr/Y structure is proposed for compensation of elastic deformations of the substrate in manufacturing highly reflective Mo/Y multilayer mirrors.

Measurement of the thickness of B4C layers deposited over metallic grids via multi-angle neutron radiography

At the present time, different kinds of thermal neutron detectors are under development at the European Spallation Source research facility, in order to overcome the well-known problem of the 3He shortage. One of these new systems relies on the use of a 3D neutron converter cathode that consists of a stack of aluminum grids, covered by a 0.9 µm 10B enriched boron carbide layer (10B4C). As the conversion efficiency is a function of the boron thickness and the mean free path of the charged particles produced in the neutron induced reaction, the characterization of the boron carbide layer uniformity over the grids becomes crucial. In this work, a non-destructive method to map the thickness distribution of the converter layer over the grids is shown. The measurements exploit the white-beam neutron radiography technique where the specimen is irradiated at different angles. This experiment has been performed at the IMAT beamline operating at the ISIS spallation neutron source (UK). The results confirm that this non-destructive, wide-ranging technique allows a reliable and fast sample characterization and that it may be exploited in similar analyses where equivalent requirements are requested.

Physical–chemical characterization of a GEM side-on 10B-based thermal neutron detector and analysis of its neutron diffraction performances

The synergic interplay between nuclear physics, detector technology and solid state and surface sciences is a fundamental aspect of the development of new neutron detection devices. The synthesis technique and the physical–chemical properties of the B4C films used as a neutron-to-charged particle converter are described in relation to the GEM side-on thermal neutron detector. Neutron detection is performed allowing scattered neutrons to be converted into charged particles by means of a series of sheets covered by 10B-enriched boron carbide (B4C) layers placed along their flight path inside the detector. The extremely interesting performance shown by the detector in neutron diffraction measurements at the ISIS spallation neutron sources are discussed and related to the chemical–physical properties of the converting layers.

Design of detector to monitor the Bragg peak location of carbon ions by means of prompt γ-ray measurements with Geant4

Real-time monitoring of the Bragg peak location of carbon ions is urgently required for the quality control of hadron therapy. In this study, we design an annular detector to monitor the Bragg peak location of carbon ions with Geant4 simulation . This $$360{^\circ }$$ surrounding structure has a high detection efficiency for the small-dose situation. The detector consists of a multilayered collimator system and an NaI scintillator for prompt gamma counting. The multilayered collimator includes a lead layer to prevent unwanted gammas and the paraffin and boron carbide layers to moderate and capture fast neutrons . An inclination of the detector further diminishes the background signal caused by neutrons. The detector, with optimized parameters, is applicable to carbon ions of different energies. In addition, the scintillator is replaced by an improved EJ301 organic liquid scintillator to discriminate gammas and neutrons. Inserting thin Fe slices into the liquid scintillator improves the energy deposition efficiency. The Bragg peak location of 200 MeV/u carbon ions can be monitored by prompt gamma detection with the improved liquid scintillator.

Fatigue of three advanced SiC/SiC ceramic matrix composites at 1200°C in air and in steam

AbstractHigh‐temperature mechanical properties and tension‐tension fatigue behavior of three advanced SiC/SiC composites are discussed. The effects of steam on high‐temperature fatigue performance of the ceramic‐matrix composites are evaluated. The three composites consist of a SiC matrix reinforced with laminated, woven SiC (Hi‐Nicalon™) fibers. Composite 1 was processed by chemical vapor infiltration (CVI) of SiC into the Hi‐Nicalon™ fiber preforms coated with boron nitride (BN) fiber coating. Composite 2 had an oxidation inhibited matrix consisting of alternating layers of silicon carbide and boron carbide and was also processed by CVI. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Composite 3 had a melt‐infiltrated (MI) matrix consolidated by combining CVI‐SiC with SiC particulate slurry and molten silicon infiltration. Fiber preforms had a CVI BN fiber coating applied. Tensile stress‐strain behavior of the three composites was investigated and the tensile properties measured at 1200°C. Tension‐tension fatigue behavior was studied for fatigue stresses ranging from 80 to 160 MPa in air and from 60 to 140 MPa in steam. Fatigue run‐out was defined as 2 × 105 cycles. Presence of steam significantly degraded the fatigue performance of the CVI SiC/SiC composite 1 and of the MI SiC/SiC composite 3, but had little influence on the fatigue performance of the SiC/SiC composite 2 with the oxidation inhibited matrix. The retained tensile properties of all specimens that achieved fatigue run‐out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.

Fatigue behavior of an advanced SiC/SiC ceramic composite with a self-healing matrix at 1300 °C in air and in steam

The fatigue behavior of a non-oxide ceramic composite with a multilayered matrix was investigated at 1300°C in laboratory air and in steam environment. The composite was produced via chemical vapor infiltration (CVI). The composite had an oxidation inhibited matrix, which consisted of alternating layers of silicon carbide and boron carbide and was reinforced with laminated woven Hi-Nicalon™ fibers. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Tensile stress-strain behavior and tensile properties were evaluated at 1300°C. Tension-tension fatigue behavior was studied for fatigue stresses ranging from 70 to 160MPa in air and in steam. The fatigue limit (based on a run-out condition of 2×105 cycles) was between 80 and 100MPa. Presence of steam had little influence on fatigue performance. The retained properties of all specimens that achieved fatigue run-out were characterized. Composite microstructure, as well as damage and failure mechanisms were investigated.

Microstructure and composition analysis of low-Z/low-Z multilayers by combining hard and resonant soft X-ray reflectivity

Microstructure and composition analysis of periodic multilayer structure consisting of a low electron density contrast (EDC) material combination by grazing incidence hard X-ray reflectivity (GIXR), resonant soft X-ray reflectivity (RSXR), and transmission electron microscopy (TEM) are presented. Measurements of reflectivity at different energies allow combining the sensitivity of GIXR data to microstructural parameters like layer thicknesses and interfacing roughness, with the layer composition sensitivity of RSXR. These aspects are shown with an example of 10-period C/B4C multilayer. TEM observation reveals that interfaces C on B4C and B4C on C are symmetric. Although GIXR provides limited structural information when EDC between layers is low, measurements using a scattering technique like GIXR with a microscopic technique like TEM improve the microstructural information of low EDC combination. The optical constants of buried layers have been derived by RSXR. The derived optical constants from the measured RSXR data suggested the presence of excess carbon into the boron carbide layer.