Compaction, structure formation, and properties of materials based on boron carbide

The effect of adding aluminum and titanium on the compactibility kinetics, structure, and properties of materials in the systems B₄C-Al and B₄C-(Ti-Al) is studied. The micromechanical properties (microhardness, microbrittleness, microstrength, and crack resistance factor (K_1c) of composite materials are determined. The influence of high pressure on the compactibility, structure, and properties of B₄C-based materials with additions of titanium and aluminum is investigated.     

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.     

Effect of structural factors on the mechanical properties of superhard materials based on boron nitride

Conclusions With increasing grain size a transition takes place from intercrystallite to dual-type (inter- and transcrystallite) fracture. The two-phase Geksanit-R is characterised by the smallest grain size, a uniform grain size, and the lowest inclusion and pore contents. It is to these characteristics that the material owes its high hardness and excellent fracture toughness (K_c50–55 kgf/mm^3/2); its effective energy of fracture, y (6.2–7.5)·10⁴ ergs/cm⁴, is an order greater than its true surface enrgy o. The hardness of Geksanit-R sinterings is virtually independent of the ratio between the relative amounts of BN_w and BN_s. The presence in Geksanit-R specimens of 2–7% of graphitelike boron nitride embrittles the material, without substantially altering its hardness. The other BN_s-base superhard materials (including Elber-R, Belbor, and PTNB-IB-1) are less hard than Geksanit-R, which is attributable to their larger grain size and the presence of foreign substances and phases, and exhibit a marked tendency toward brittle rupture.Translated from Poroshkovaya Metallurgiya, No. 10(202), pp. 61–69, October, 1979.     

不同氮气压力烧结对WC-TiC-NbC-Co硬质合金表面结构和性能的影响

采用不同氮气压力烧结制备WC-TiC-NbC-Co合金,再使用CVD方法进行涂层.通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射分析仪(XRD)、表面粗糙度仪和划痕测试仪对烧结后及涂层后的样品表面形貌、成分、物相、粗糙度及涂层结合力进行表征与测量.结果表明,与真空烧结相比,在氮气氛中烧结的WC-TiC-NbC-Co硬质合金样品的表面形成了以TiC相为主的梯度层,梯度层厚度随着氮气压力的升高而增大.当氮气压力为15 kPa时,梯度层厚度达到了10μm,当氮气压力为10 kPa时,样品与CVD涂层具有最好的结合力.说明适当的氮气压力可以在合金表面形成一定厚度梯度层,并有助于提高涂层结合力.     

不同氮气压力烧结对WC-TiC-NbC-Co硬质合金表面结构和性能的影响

采用不同氮气压力烧结制备WC-TiC-NbC-Co合金,再使用CVD方法进行涂层.通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射分析仪(XRD)、表面粗糙度仪和划痕测试仪对烧结后及涂层后的样品表面形貌、成分、物相、粗糙度及涂层结合力进行表征与测量.结果表明,与真空烧结相比,在氮气氛中烧结的WC-TiC-NbC-Co硬质合金样品的表面形成了以TiC相为主的梯度层,梯度层厚度随着氮气压力的升高而增大.当氮气压力为15 kPa时,梯度层厚度达到了10μm,当氮气压力为10 kPa时,样品与CVD涂层具有最好的结合力.说明适当的氮气压力可以在合金表面形成一定厚度梯度层,并有助于提高涂层结合力.     

不同氮气压力烧结对WC-TiC-NbC-Co硬质合金表面结构和性能的影响

采用不同氮气压力烧结制备WC-TiC-NbC-Co合金,再使用CVD方法进行涂层.通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射分析仪(XRD)、表面粗糙度仪和划痕测试仪对烧结后及涂层后的样品表面形貌、成分、物相、粗糙度及涂层结合力进行表征与测量.结果表明,与真空烧结相比,在氮气氛中烧结的WC-TiC-NbC-Co硬质合金样品的表面形成了以TiC相为主的梯度层,梯度层厚度随着氮气压力的升高而增大.当氮气压力为15 kPa时,梯度层厚度达到了10μm,当氮气压力为10 kPa时,样品与CVD涂层具有最好的结合力.说明适当的氮气压力可以在合金表面形成一定厚度梯度层,并有助于提高涂层结合力.     

不同氮气压力烧结对WC-TiC-NbC-Co硬质合金表面结构和性能的影响

采用不同氮气压力烧结制备WC-TiC-NbC-Co合金,再使用CVD方法进行涂层.通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射分析仪(XRD)、表面粗糙度仪和划痕测试仪对烧结后及涂层后的样品表面形貌、成分、物相、粗糙度及涂层结合力进行表征与测量.结果表明,与真空烧结相比,在氮气氛中烧结的WC-TiC-NbC-Co硬质合金样品的表面形成了以TiC相为主的梯度层,梯度层厚度随着氮气压力的升高而增大.当氮气压力为15 kPa时,梯度层厚度达到了10μm,当氮气压力为10 kPa时,样品与CVD涂层具有最好的结合力.说明适当的氮气压力可以在合金表面形成一定厚度梯度层,并有助于提高涂层结合力.     

Effect of porosity and grain size on the mechanical properties of hot-pressed boron carbide

Conclusions An investigation was carried out into the effect of porosity in the range 2–46% and grain size in the range (5–140)·10^–6 m on the mechanical properties of boron carbide. It is shown that the level of mechanical properties of boron carbide produced by hot pressing from powders synthesized from the elements is 1.5 times higher than that of boron carbide produced by other methods. Increasing the porosity of boron carbide to 46% decreases its strength by a factor of six or seven. Increasing the grain size to 140·10^–6 m has the same effect. An analysis is made of equations describing the dependence of the mechanical properties of boron carbide on porosity and grain size. The constants of these equations have been determined.Translated from Poroshkovaya Metallurgiya, No. 1(229), pp. 63–67, January, 1982.     

助烧体系对注射成形碳化硼陶瓷烧结性能的影响

采用粉末注射成形技术制备碳化硼陶瓷微结构零件,用SiC-Al2O3-Y2O3和SiC-ZrO2两种助烧体系进行烧结。分析助烧体系(SiC-Al2O3-Y2O3和SiC-ZrO2)对零件的致密度、相组成、微观组织和断裂机制的影响。结果表明:添加助烧剂可有效提高碳化硼制品的烧结性能。采用SiC-Al2O3-Y2O3助烧体系烧结的零件由B4C、SiC、B2YC2和YAG等4种相组成,随烧结温度升高,其致密度先增加后减小,在1 950℃烧结时达到最大值,为97.1%。而采用SiC-ZrO2助烧体系时致密度随烧结温度升高而增加,在2 240℃达到最大值,为95.1%,相组成为B4C、SiC和ZrB2相。零件的断裂形式都以穿晶断裂为主,含有一定的沿晶断裂。     

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.     

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.     

Effect of an oxide coating on the strength properties of boron and silicon carbide fibers

Institute of Materials Science Problems, Academy of Science of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 6(366), pp. 55–61, June, 1993.