Effect of high pressure on the structure and properties of materials based on boron carbide

The effect of high pressure on the structure and properties of B₄C-SiC and B₄C-Al ceramics is studied. The effect of high pressure on micromechanical properties and crack resistance factor K_Ic of composite materials is investigated. High isostatic pressure treatment at 1300–1400°C leads to improvement of material mechanical properties and structure.     

Electroerosion behavior of a ceramic based on boron carbide: Phase composition, structure, and properties of protective spark coatings

Measurements have been made on the erosion resistance of B₄C-15% TiB₂ materials made by reactive sintering on hot pressing of B₄C-TiO₂-C powder mixtures. The composite material is used as an electrode for treating steel and titanium surfaces in spark alloying. It is shown that the method of preparing the boron carbide influences the erosion resistance of the ceramic much less than it does for the mechanical properties. The surface layers of the electrode materials are affected by the electrical discharge and give rise to secondary structures because of chemical interaction between the electrode materials on the one hand and elements in the gas medium on the other. The properties of these structures are responsible for the erosion characteristics of the electrode material and for the compositions and qualitative properties of the coatings.     

Effect of annealing on the structure and properties of hot-pressed boron carbide base cermets

Conclusions During the annealing of a hot-pressed boron carbide-aluminum materials at a temperature exceeding the melting point of aluminum intense formation of-AlB₁₂ takes place. This has a deleterious effect on the strength properties (transverse rupture strength _tr, fracture toughness k_Ic, and impact strengtha) of the material and increases its hardness and electrical resistivity. It follows therefore that, to obtain boron car-bide-aluminum materials of maximum strength, it is necessary to perform their liquid-phase pressing under high pressures (above 0.5 GPa) and dispense with subsequent annealing. Annealing at a temperature below the melting point of aluminum brings about only very small changes in the structure of the material, and the resultant fall in hardness is less than the increase in hardness. Consequently, when it is necessary to increase the hardness of the material and a slight loss of strength is acceptable, recourse may be had to low-temperature annealing (below 660°C).Translated from Poroshkovaya Metallurgiya, No. 9(273), pp. 51–54, September, 1985.     

Phase composition, structure, and properties of aluminum materials mechanically alloyed with boron

The paper focuses on the formation of phase composition, structure, and properties of high-strength aluminum materials that are mechanically alloyed with boron and have a large effective thermal-neutron capture cross-section. A technology based on reactive mechanical alloying is proposed. It is intended to produce dispersion-hardened nanostructured materials in the Al-B system. Structural high-temperature materials with a low density and a great effective thermal-neutron capture cross-section can be obtained by complex alloying of aluminum with elemental boron (up to 40%) and B₂O₃ (1.5%). When the boron content reaches its maximum (40%), the strength of the material is σ_t = 380 MPa and σ ₁₀₀ ⁵⁰⁰ = 101 MPa; when the boron content decreases to 10%, the strength increases to σ_t = 560 MPa and σ ₁₀₀ ⁵⁰⁰ = 150 MPa.     

Sintered ceramics based on boron nitride and carbide

The formation of BN-B₄C composite materials by sintering in nitrogen is investigated. Structural, mechanical, and chemical characteristics of these materials are examined. Excellent dielectric properties, thermal and chemical stability, and erosion resistance in high-intensity laser beams enable high-temperature application of BN-B₄C composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 58–63, 2007.     

Temperature effect on bending strength of hot-pressed boron carbide materials

The paper examines three groups of samples based on B₄C and B₁₃C₂ powders (with additions of Al and Al₂O₃ in the amount of 2 and 5 wt.%, respectively). It is established that the maximal strength (445 MPa) is characteristic of the material B₁₃C₂ over the whole temperature range. It does not change up to 1600°C. The increase in strength of B₄C-based samples is revealed over the range of 1200 to 1600°C, mainly for high-porous materials (10–12%). Presumably, this is due to the higher relaxation properties of porous material microstructure. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 60–68, 2007.     

Synthesis, heat resistance, and optical properties of boron silicide and materials based on it

Conditions of synthesis from elements of pure superfine powder of boron silicide B₄Si are investigated. It is shown that the silicide phase forms on boron particles and B₄Si particles inherit the shape and size of initial boron particles, which makes it possible to control the particle size of the powder obtained. The oxidation of pure boron silicide and materials based on it in air and their optical properties are studied. It is shown that chromium diboride added to boron silicide increases the oxidation resistance of B₄Si and hardly decreases its absorbance. The B₄Si-CrB₂ material can be successfully introduced into the compositions of heat-protective coatings operating in air at 1300 °C. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 45–52, 2007.     

Frictional properties of materials based on dense modifications of boron nitride

Conclusions For all of the dense modifications of boron nitride under conditions of loading by friction upon reaching the critical sliding rate a qualitative change in the frictional characteristics is observed. On the working surface of the abradant a film is formed, which obviously is an indication of transformation of the sphalerite and wurtzite phases into the graphitelike one with subsequent oxidation of it and the formation of low-melting iron borates.By changing the ratio of the content of dense modifications of boron nitride (BN_sph and BN_w) it is possible to control the critical value of V within a wide range of sliding rates, thereby obtaining the optimum combination of frictional characteristics, which is of significant value in practical machining of materials.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 82–87, September, 1984.     

The preparation and some properties of materials on the base of silicon carbide with boron and aluminum additions

Summary An investigation was conducted on the modes of sintering samples of silicon carbide with additions of boron and aluminum by hot pressing, and some physical properties of the resulting alloys were studied.     

碳化硼在吸收材料中的地位及其与核应用有关的基本性能

对碳化硼与其它材料的中子吸收截面、吸收效率、价格进行了比较,综述了作为吸收材料的碳化硼在世界核反应堆中的地位,综述了影响碳化硼核应用的有关性能(均相区范围、热导率、比热容、热膨胀系数)的研究结果,并与报道的实验数据进行了校验,讨论了碳化硼的抗水腐蚀能力。