Increase Of BN Content Research Articles

Effect of BN addition on mechanical and electrical properties of oxidative sintered porous Si3N4-BN composites

In order to explore the effects of BN addition on the mechanical and electrical properties of oxidative sintered Si3N4-BN composites, Si3N4-BN composites with BN powder dosage of 0-40 wt% are prepared by molding technology, and the effects of different BN contents on the phase, morphology, bulk density, porosity, flexural strength at room temperature, dielectric constant and dielectr loss of the composite system are studied. With the increase of BN content, at different temperatures, the oxidation product B2O3 of BN and the oxidation product SiO2 of Si3N4 firstly react on the surface to form B2O3–SiO2 glass phase, which densify the surface and affects the oxidation degree of internal grains. At the same time, a small amount of B2O3 escaping from the surface, so that the open pores of the composites decrease firstly and then increase slightly, and the dielectric constant increases firstly and then decreases. The results show that when the amount of BN micronized powder is 10 wt%, the oxidation sintered Si3N4-BN composite material at 1500 °C have pores that retain the sheet structure of boron nitride, and the amorphous material flows to fill the pores, so it have high volume density (1.85 g/cm3), low porosity (apparent porosity 6.37%), and high mechanical properties (flexural strength 127.86Mpa), higher dielectric constant (3.94) and lower dielectr loss (4.0 × 10−4).

High performance of FeSiAl/hBN soft magnetic composites

FeSiAl/hBN soft magnetic composites were prepared by mixing gas atomized FeSiAl powder and hexagonal BN by ball milling at a certain mass ratio and then compacted and annealed. The microstructure of the composites was characterized by XRD, SEM and EDS. It was found that ball milling can destroy the weaker interlayer bond of hexagonal BN and turn it into nanoflakes attached to the surface of FeSiAl particles. The magnetic properties of the composites were measured by SQUID and B-H analyzer. It was found that the nanoflakes on the surface of FeSiAl particles effectively blocked the eddy current among different metallic particles and largely reduced eddy current loss. The permeability analysis showed that the composites had a relative lower magnetic loss at f = 30 MHz, which indicated that the FeSiAl/hBN composites can be used in a frequency higher than other FeSiAl composites. However, the saturation magnetization and permeability of the composites decreased with the increase of BN content. The experimental results show that the magnetic loss value of FeSiAl/1 wt% hBN soft magnetic composites is about 392 kW m−3 at f= 100 kHz and Bm= 100mT, which is just about 2/3 of commercial FeSiAl soft magnetic composites.

Preparation and characterization of BN modified PA6/PC thermal conductive composites

ABSTRACT In this paper, BN was used for composite modification of the PA6/PC incompatible blends, and the effects of BN filling amount on thermal conductivity of PA6/PC/BN multiphase composites were systematically studied. Results indicated that compared with single-phase matrix composites, the two-phase matrix exhibited slightly better thermal conductivity under the same amount of BN. At the same time, the thermal conductivity of PA6/PC/BN gradually increased with the increase in BN content. When the BN content was 33.33 wt%, the thermal conductivity of PA6/PC/BN composite reached the maximum value of 0.953 W/(m·K), which was about 4.5 times of the matrix. In addition, the content of BN had a great influence on the melting crystallization behavior of the composite, and the addition of BN had a significant increase in the crystallization temperature of the materials.

Pressureless solid-state sintering of SiC ceramics with BN and C additives

ABSTRACT This study proposes BN as a new sintering aid for pressureless solid-state sintering of SiC ceramics. The full densification of SiC ceramics for 0.5–2.7 wt% BN addition showed the composition tolerance of the newly developed ceramics. The electrical resistivity decreased by an order of magnitude (107→106 Ω·cm) as BN content increased from ~0.5 to ~0.9 wt% because of the increased BN-derived B doping in the SiC lattice. A further increase in BN content had no significant effect on the electrical resistivity, which is attributed to the limited solubility of B in the SiC lattice. The thermal conductivity decreased with increasing BN content owing to increased phonon scattering at B-doped sites and the thermally insulating BN phase located at the grain boundaries. The fracture toughness increased with increasing BN content owing to interfacial debonding at the weak SiC-BN interfaces. However, intrinsically weak BN grains with low hardness were responsible for reduced flexural strength and hardness with increasing BN content.

Effect of Boron Nitride Addition on Densification, Microstructure, Mechanical, Thermal, and Dielectric Properties of β-SiAlON Ceramic

In this present communication, an investigation was carried out to examine the influence of hexagonal boron nitride (h-BN) powder addition and its particle size on the density, microstructure, mechanical, thermal, and dielectric properties of h-BN containing β-SiAlON ceramic. It was observed that with the increase in BN content up to 5 wt.% in starting composition, the bulk density of β-SiAlON decreases drastically from 3.22 (for pristine SiAlON) to 3.05 g/cm3 and 2.90 g/cm3 for small and large particle size containing β-SiAlON, respectively. The bulk density and mechanical properties such as Young’s modulus, Vickers hardness, flexural strength, and fracture toughness of pristine β-SiAlON are superior in comparison with both types of β-SiAlON-BN ceramic. On the other side, the density and mechanical properties of β-SiAlON prepared with fine BN powder show superior value compared to that of larger BN particle-added β-SiAlON. The thermal properties such as thermal conductivity for both BN powder-added β-SiAlONs are higher compared to that of pristine β-SiAlON. However, larger BN particle-added β-SiAlON exhibits superior thermal conductivity than that of fine BN powder-added β-SiAlON. The dielectric constant of h-BN-added SiAlON is relatively lower than that of pristine β-SiAlON.

Active metal brazing of SiO2–BN ceramic and Ti plate with Ag–Cu–Ti + BN composite filler

SiO2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti+BN composite filler. The effect of BN content, brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated. The results showed that a continuous TiN–TiB2 reaction layer formed adjacent to the SiO2–BN ceramic, whose thickness played a key role in the bonding properties. Four Ti–Cu compound layers, Ti2Cu, Ti3Cu4, TiCu2 and TiCu4, were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag. The central part of the joint was composed of Ag matrix, over which some fine-grains distributed. The added BN particles reacted with Ti in the liquid filler to form fine TiB whiskers and TiN particles with low coefficients of thermal expansion (CTE), leading to the reduction of detrimental residual stress in the joint, and thus improving the joint strength. The maximum shear strength of 31MPa was obtained when 3wt% BN was added in the composite filler, which was 158% higher than that brazed with single Ag–Cu–Ti filler metal. The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content, brazing temperature and holding time. Based on the correlation between the microstructural evolution and brazing parameters, the bonding mechanism of SiO2–BN and Ti was discussed.

Effect of BN content on the mechanical and dielectric properties of porous BNp/Si3N4 ceramics

Porous BNp/Si3N4 ceramics were prepared by gas pressure sintering method as a candidate wave-transparent material. The effects of BN particle additions ranging from 0wt% to 15wt% on the phase compositions, microstructures, mechanical performance and dielectric properties were investigated. With the increase of BN content, the apparent porosity of the BN/Si3N4 ceramics increased greatly from 2.3% to 21.2%. Although the mechanical properties were partially weaken, the dielectric performance of the porous BN/Si3N4 was largely enhanced at the same time. For the 10% BN/Si3N4 porous composite ceramics, the permittivity and dielectric loss was 33.5% and 62.2% lower than that of the porous Si3N4 without BN content, respectively. Specifically, when 10% BN particles were added, the porous BNp/Si3N4 has a porosity of 20.5% and the permittivity and dielectric loss were 5.14 and 0.0085 respectively with bending strength of 190.1MPa and fracture toughness of 4.16MPam1/2, which can meet the required value of wave transparent materials.

Interfacial microstructure and strengthening mechanism of BN-doped metal brazed Ti/SiO2-BN joints

Ag–Cu–Ti + BN composite filler was developed to braze SiO 2 -BN ceramic and titanium. The effects of BN particles content on the microstructure and mechanical properties of the joints were investigated. The fine TiB whiskers and TiN particles were synthesized in the brazing seam by introducing BN particles. TiN–TiB 2 reaction layer formed adjacent to SiO 2 -BN ceramic while Ti–Cu compound layer formed at Ti substrate. With the increase of BN content, more fine-grains formed in the joint and the reaction layer nearby the base materials became thinner. The hardness and modulus of the reaction phases were characterized by nanoindentations to reveal the plastic deformability of the brazing seam. The improvement of the joint strength was 340% with 3 wt.% BN addition. The joint strength was determined by the thermal expansion mismatch between the joined materials, plastic deformation in the brazing seam, and interfacial structure of the joint.

Fabrication of translucent boron nitride dispersed polycrystalline silicon nitride ceramics

Optical transparency was achieved at infrared region and overall translucent silicon nitride was fabricated using hot press sintering (HPS). The increase in h-BN content decreased the optical transparency. Microstructral observations shows that the optical, mechanical and tribological properties of BN dispersed polycrystalline Si3N4 ceramics were affected by the density, α:β-phase ratio and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN at 1850°C. The composite contained from 0.25 to 2 mass % BN powder with sintering aids (9% AlN + 3% MgO). Maximum transmittance of 57% was achieved for 0.25 mass % BN doped Si3N4 ceramics. Fracture toughness was increased and wear volume and friction coefficient were decreased with increase in BN content.

Optical, Mechanical and Tribological Properties of Boronnitride Dispersed Silicon Nitride Ceramics

Transparent ceramics are used in new technology because of their excellent mechanical properties over glasses. Transparent ceramics are nowadays widely used in armor, laser windows, and in high temperature applications. Silicon nitride ceramics have excellent mechanical properties and if transparent silicon nitride is fabricated, it can be widely used. h-BN has a lubricating property and is ductile. Therefore, adding h-BN to silicon nitride ceramics gives a lubricating property and is also machinable. Translucent silicon nitride was fabricated by hot-press sintering (HPS) and 57% transmittance was observed in the near infrared region. A higher wt. % of h-BN in silicon nitride ceramics does not favor transparency. The optical, mechanical, and tribological properties of BN dispersed polycrystalline ceramics were affected by the density, -phase ratio, and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of , AlN, MgO, and h-BN at . The composite contained from 0.25 to 2 wt. % BN powder with sintering aids (9% AlN + 3% MgO). A maximum transmittance of 57% was achieved for the 0.25 wt. % BN doped ceramics. Fracture toughness increased and wear volume and the friction coefficient decreased with an increase in BN content. The properties such as transmittance, density, hardness, and flexural strength decreased with an increase in content of h-BN in silicon nitride ceramics.

Complex Study of Single‐Walled Nanotubes Synthesized from C:BN Mixtures

A complex characterization of single‐walled nanotubes, synthesized by arc‐discharge from different mixtures of layered materials (graphite and hexagonal BN), have been performed with Raman spectroscopy, UV‐VIS‐NIR optical absorption spectroscopy and high‐resolution transmission electron microscopy. The optical absorption bands of single‐walled nanotubes synthesized from C:BN mixture were blue‐shifted comparing to those of pure carbon nanotubes, synthesized under the same conditions. This shift may arise due to embedding of BN fragments into the nanotube walls. The intensity redistribution of the “breathing” modes, observed in the Raman spectra of nanotubes grown from C:BN mixture, is considered as a decrease of nanotube diameters with an increase of BN content in the initial mixture.

Mechanical properties and microstructures of hot-pressed MgAlON–BN composites

The relationship between the mechanical properties and microstructure of hot-pressed MgAlON–BN composite materials was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and X-ray diffraction (XRD) techniques. The phase compositions of hot-pressed samples prepared from starting mixtures of Al 2O 3, AlN, MgO and h–BN consisted of MgAlON phases as a matrix and BN phases as the second phase. The density, bending strength at room temperature, fracture toughness and Vickers hardness were measured. The results indicated that the density, strength and Vickers hardness decrease with increasing h–BN content due to the non-reactive nature and layered structure of h–BN. The fracture toughness, however increased with increasing h–BN addition, reaching a maximum of 3.64 MPa m 0.5; it decreased with further increase of BN content. The increase of fracture toughness was attributed to the presence of microcracks and the decrease was considered to be the discontinuous microstructure of the MgAlON phases. Temperature dependence of bending strength remained constant at low temperature, followed by an increase at 800 °C and then, dropped quickly. The increase in the bending strength of the composite was attributed to the decrease of residual stress and to the interwoven microstructure of the composites which prevented grain boundary slip and reduced the attenuation rate of high temperature strength. The machinability of the composites was examined. The results indicate that the composite materials with BN content more than 15 vol.% exhibit excellent machinability and could be drilled using conventional hard metal alloy drills.

Fabrication and properties of machinable 3Y–ZrO 2/BN nanocomposites

3Y–ZrO 2/BN ceramic composites with nano-sized BN dispersoids ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing turbostratic BN (t-BN) coating 3Y–ZrO 2 powders, which were prepared via in situ reaction between boric acid and urea on the surface of 3Y–ZrO 2 particles in nitrogen gas. XRD analysis and TEM observations revealed that the nano-sized turbostratic and hexagonal BN (t/h-BN) particulates were dominantly dispersed at ZrO 2 grain boundaries. Vickers hardness of materials decreased directly with an increase of BN content. The fracture strength and the fracture toughness were considerably improved, in comparison to corresponding 3Y–ZrO 2/BN microcomposites. The nanocomposites with BN content more than 20 vol.% were ready for machining. The preliminary information on the relationship between microstructures and properties are provided.

Machinable Al 2O 3/BN composite ceramics with strong mechanical properties

Al 2O 3/BN composite ceramics with nano-sized BN dispersions ranging from 0 to 30 vol.% were successfully fabricated by hot-pressing α-Al 2O 3 powders with turbostratic BN (t-BN) coating, which was prepared through chemical processes using boric acid and urea. SEM observations revealed that the nano-sized hexagonal BN (h-BN) particulates were homogeneously dispersed within Al 2O 3 grains as well as at grain boundaries. Vickers hardness of materials decreased with an increase in BN content. The fracture toughness was improved but the fracture strength had a small decrease, in comparison to Al 2O 3 monolithic ceramics. The nanocomposite ceramics with BN content more than 20 vol.% exhibited excellent machinability, which could be drilled using conventional hard metal alloy drills. Drilling rates and normal forces demonstrate the ease of machining of these materials. The preliminary information on the relationship between microstructures and properties are provided. The mechanism of material removal is also discussed.

In situ Si 3N 4–SiC–BN composites: preparation, microstructures and properties

Boron nitride composites in Si–B–C–N system have been widely studied and applied in industry in these decades. In the present investigation, in situ reaction process was used to fabricate a new kind of silicon nitride-silicon carbide-boron nitride (Si 3N 4–SiC–BN) composites according to a previously proposed reaction of Si 3N 4, B 4C, and C with extra addition of Si 3N 4 in the starting powder mixture. The composites were produced by hot pressing at 1800 °C in a nitrogen atmosphere. The obtained composites demonstrated relatively high density and high bending strength over those of conventionally-processed ones, although with increasing BN content the densification behavior became poorer especially for composites with BN contents higher than 25 vol.%. The growth of rodlike β-Si 3N 4 grains was suppressed in the composites. Different from the previously reported SiC–BN in situ composites in which the strength almost kept unchanged when the BN content was lower than 35 vol.%, the strength of the present Si 3N 4–SiC–BN composites decreased monotonously with increase in BN content due to the decreased relative density and limited grain growth of rodlike β-Si 3N 4 grains.

希土類元素とB添加による高張力鋼の大入熱溶接ボンド部の組織と靱性の改良

For the purpose to improve the weld bond toughness through ferrite grain refinement in 40-60kg/mmmm2 tensile strength steels, the effects of various alloying elements on the grain structure and notch toughness in the weld bond were investigated. Of the alloying elements investigated, small additions of both rare earth metal (REM) and boron (B) were found to accelerate the formation of fine ferrite grains inside prior austenite grains, resulting in a remarkable improvement weld bond thoughnss.The main results obtained are summarized as follows:(1) The optimum concentration range of REM and B are 0.020-0.040% and 0.0020-0.0035%, respectively.(2) With an increase of BN content, the number of fine ferrite grains increases remarkably.(3) The amount of BN re-precipitated during welding thermal cycle is larger in REM-B steel than in B steel.(4) Spherical inclusions are frequently observed in the center of ferrite grains or adjacent to them and many of them identified as Ce2O2S and BN.(5) According to the observation by IMMA, the location of B+-images is in good accordance with that of both Ce+-and N+-images.By the use of commercial heats of REM-B steel, brittle fracture tests were conducted and good results were obtained.