Composites with zirconium matrix reinforced with boron and silicon carbide fibers

Structural features of a composite material (CM) consisting of a plastic zirconium foil-like matrix reinforced with continuous high-strength fibers of boron or silicon carbide with a diameter of 100 μm (25 to 30 vol.%) are examined at testing temperatures up to 950 °C. Model specimens are compacted by diffusion welding in vacuum at 1100 °C. Structural studies reveal a diffusion interaction area at the fiber-matrix interface. Cracks and pores appear in the area at 1100 °C. The effect of the diffusion area thickness on CM mechanical properties is discussed. It is established that reinforcement of zirconium with B or SiC fibers provides 7 and 5 times higher strength at 950 °C, respectively. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 48–53, 2007.     

Two-step rapid thermal diffusion of boron into silicon using a boron nitride solid diffusion source

A two-step rapid thermal diffusion process of boron into silicon using a boron nitride solid diffusion source is described. During the first step, HBO² glass is transferred onto the silicon wafer from the diffusion source by keeping the temperature of the silicon wafer at 750° C while the diffusion source is at about 900° C. Boron is, then, diffused into the silicon wafer from HBO² glass at 1000° C or 1100° C in N₂ during the second step. Extremely shallow junctions with junction depths of about 20 nanometers and sheet resistances of about 350 ohms/sq can be achieved with this method as well as relatively deep junctions with junction depths of about 175 nanometers and sheet re-sistances of about 55 ohms/sq. When the diffusion is performed at 1100° C, both the junction depth and electrically active boron concentration at the surface increase as the ambient gas is changed from N₂ to O₂ while the sheet resistance decreases. A boron rich layer which has high resistivity is not formed at the surface when the diffusion is performed at 1100° C in O₂ ambient. This work was supported by Ministry of Science and Technology, Korea     

Effect of Amount of Boron Doping on Compression Deformation of Fine-Grained Silicon Carbide at Elevated Temperature

The effect of the amount of boron doping in the range of 0 to 1.0 wt% on the high-temperature deformation of fine-grained β-silicon carbide (SiC) was investigated by compression testing. Flow stress at the same grain size increased as the amount of boron doping decreased. The stress exponent increased from 1.3 to 3.4 as the amount of boron doping decreased. The strain rates of undoped SiC were ∼2 orders of magnitude lower than those of 1.0-wt%-boron-doped SiC of the same grain size. The apparent activation energies of SiC doped with 1.0 wt% boron and of undoped SiC were 771 ± 12 and 884 ± 80 kJ/mol, respectively. These results suggest that the actual contribution of grain-boundary diffusion to the accommodation process of grain-boundary sliding decreased as the amount of boron doping decreased. Consequently, the apparent contribution of the dislocation glide increased.     

Effect the Actual Structure of Boron and Catalytic Additions on Boron Nitride Synthesis

The bahavior of boron with different degrees of purity, fineness, and crystal structure perfection during nitriding at high temperature is studied by electron microscopy, x-ray diffraction, and chemical analysis. The effect of additives (Li₂CO₃, H₃BO₃, and NH₄Cl) on boron nitride synthesis is studied. A marked reduction is established in the temperature for forming a highly-ordered boron nitride structure on introducing additives. The chemistry of the amorphizing effect of ammonium chloride on the crystal structure of boron is suggested.     

Chemical Vapor Deposition in the Boron-Carbon-Nitrogen System

The preparation of a two-phase coating of B₄C-BN was addressed as a potential wear coating because of its likelihood of having a high fracture toughness resulting from its composite nature and inherent lubrication due to the presence of BN. Equilibrium analysis identified appropriate deposition conditions; however, deposited coatings were found to be single-phase BN with a high degree of substitution of carbon for nitrogen.     

Parameter spaces for the nucleation and the subsequent growth of cubic boron nitride films

The data existing in the literature about the deposition of cubic boron nitride thin films were reviewed critically in order to establish the parameter spaces of c-BN nucleation and growth. The ion energy E_i, the flux ratio F (=incoming ions/incoming boron atoms), the ion mass m_i, (or the ratio Ar/N₂, respectively), and the substrate temperature T_s, had already been identified as the decisive parameters which are, however, interdependent. Earlier data collections on c-BN deposition had shown that, irrespective of the deposition technique used, a well-defined c-BN region exists in the F/E_i parameter space, in which the deposition of c-BN is possible. Similar regions exist in the F/m_i and F/T_s parameter spaces. The present collection extends these older diagrams considerably, especially to the low energy region. From this extention it can be concluded that the momentum transfer concepts proposed in the literature fail to explain the data. Furthermore, the older collections were considered valid for nucleation and growth likewise. However, in recent years data have been published showing that the boundaries of the c-BN regions are different for nucleation and growth. After successful nucleation, subsequent growth can occur either at reduced ion bombardment (either energy or flux ratio or ion mass) and also at reduced temperatures. The existing data for this parameter reduction have been collected in this paper. It will be shown that the growth depends in a similar way as the nucleation on the (interdependent) ion bombardment parameters but no longer on temperature. This means that the nucleation and growth of c-BN are based on different, although in both cases ion-induced, mechanisms.     

Electron spectroscopic imaging of antigens by reaction with boronated antibodies

Two small homogeneous markers for electron spectroscopic imaging (ESI) containing eight dodecaborane cages linked to a poly-α,ε- l -lysine dendrimer were synthesized; one of these was made water soluble by the attachment of a polyether. The markers were coupled to the sulfhydryl group of (monovalent) antibody fragments (Fab') by a homobifunctional cross-linker. While the coupling ratios of the poorly water-soluble compound did not exceed 20%, the polyether-containing variant reacted quantitatively. Its suitability for immunolabelling was tested in a study of the mechanism of the transcellular transport of an administered heterologous protein (bovine serum albumin, BSA) through ileal enterocytes of newborn piglets by endocytotic vesicles in comparison to conventional immunogold reagents. The post-embedding technique was employed. The boronated Fab' gave rise to considerably higher tagging frequencies than seen with immunogold, as could be expected from its form- and size-related physical advantages and the dense packing of BSA in the vesicles. The new probe, carrying the antigen-combining cleft at one end and the boron clusters at the opposite end of the oval-shaped conjugate, add to the potential of ESI-based immunocytochemistry.     

内燃机强化的新思维——铝硅合金活塞裙部表面进行CBN超硬、抗磨覆膜强化

过共晶铝硅合金活塞的裙部表部经等离子渗硅与多晶立方氮化硼(PCBN)聚晶沉积薄膜所构成的双层覆膜强化后，既能保全铝硅合金活塞整体的高强度、高刚度与优良的耐热性能，又能显著提高其裙部表面的抗胶合性能和耐磨性能。对这些新颖的表面强化工艺中的几种生产率最高的强化工艺进行对比性论述，同时探讨这几种新工艺与现行活塞表面处理的工艺性衔接问题，并对此工艺在生产实践中推广应用进行预测。     

Interactions between intrinsic defects and nitrogen/boron impurities in high-resistivity 4H SiC: Electron paramagnetic resonance study

Electron paramagnetic resonance (EPR) has been employed to examine thermo- and photo-activated interactions between as-grown intrinsic defects and nitrogen/boron impurities in nominally high-resistivity 4H SiC produced without intentional vanadium doping. The EPR spectra, recorded in the dark at 4 K, revealed either a low concentration of paramagnetic boron, nitrogen, or a carbon-vacancy-related defect (ID-1). The photo-induced charge transfer between ID-1 and both boron and nitrogen has been detected. In some samples, illumination with 0.9–1.6-eV light at 4.2 K quenched the ID-1 signal and produced an approximately equal amount of shallow paramagnetic boron. Exposure to 1.9–2.7-eV light restored the ID-1 center and produced shallow paramagnetic nitrogen. A model based on excitation from the band edges and the threshold energies obtained from the photo-EPR data placed the ID-1 level 0.9±0.1 eV above the valence-band edge. Comparison of these data with that obtained from other samples that exhibited excess boron or nitrogen impurities suggested the presence of an additional defect no more than 0.9 eV below the conduction-band edge. This defect can exchange charge with the nitrogen donor.