Structure and Deformation of Intermetallic Beryllides

Intermetallic beryllides are potential light-weight, high-temperature structural materials. In this paper. the processing techniques, microstructure. deformation, and oxidation properties of intermetallic beryllides are described. In addition to nickel beryllides (NiBe). which is treated as a model system.other high beryllium-containing refractory beryllides, such as Nb2 Be17. VBe12. are also studied.The room temperature deformation and high-temperature creep properties of these beryllides are repor4ed. At room temperature. NiBe exhibits certain tensile ductility (~ 1 .3%). but all other beryllides are essentially brittle. Nonetheless, these beryllides become ductile at temperatures above approximately 1000℃. Their creep properties are presented. The creep properties are compared with those of intermetallic aluminides. Also. a comparison is made between the ductile-to-brittle transition behaviour of intermetallic beryllides and that of aluminides. Although beryllides are generally oxidation resistant at high temperatures, some beryllides, e.g., ZrBe13, suffer the pest reaction during oxidation at intermediate tem peratures. The pest mechanisms are proposed     

CVD金刚石膜超精密度刀具技术研究

文章对CVD金刚石的物理特性进行了描述,研究了CVD金刚石膜制作超精密刀具的工艺技术方法,设计了生产工艺流程,对生产的CVD金刚石膜直刃和圆弧超精密刀具的精度及加工件的精度进行了测试,表明CVD金刚石膜是一种非常优异的超精密刀具的制作材料,应用前景非常广阔.     

Simulation of dual firing of hydrogen-rich reformate and JP-8 surrogate in a swirling combustor

Flame control, particularly at very lean conditions, is a critical requirement for external combustion power sources such as thermoelectric and thermophotovoltaic generators. The availability of in-situ produced hydrogen from JP-8 fuel reforming presents a potential supply of hydrogen at the application site, such as the battlefield, without adding a second fuel to the logistics system. This research investigates the use of small amounts of hydrogen co-fired with JP-8 for improved energy efficiency, operational flexibility and environmental protection. Numerical simulations were conducted in a 6 kW (thermal) swirling flow combustor under different conditions. The simulations use hydrogen and a single hydrocarbon surrogate for JP-8 with a 4-step reaction mechanism. It also examined the effect of using hydrogen-rich reformate containing hydrogen, carbon monoxide and other gases dual-fired with JP-8. Results showed that at lean conditions, dual firing of hydrogen or reformate with JP-8 provided improved fuel conversion, better flame stability and higher fuel burnout. Dual firing hydrogen-rich reformate and JP-8 led to increased burner capacity, reduced system size and weight requirements. However, dual firing with hydrogen provided little benefit to JP-8 combustion under stoichiometric or fuel rich conditions because they were limited by mixing rather than chemical kinetics. These results indicate that dual firing of hydrogen with JP-8 is a promising method for improving lean flame stability and burner control. This has the potential to enable small scale power applications with specific temperature requirements such as thermoelectric and thermophotovoltaic generators.     

Simulation investigation on supercontinuum generation and noise characteristics in the normal dispersion photonic crystal fiber with a flattened dispersion profile

The propagation of picosecond pulses in the normal dispersion photonic crystal fiber(PCF) with a flattened dispersion profile is numerically investigated.The characteristics of the amplitude and phase noise in the supercontinuum generation(SCG) are also analyzed through the coherent sliced supercontinuum(SC).The effects of self-phase modulation(SPM) and four-wave mixing(FWM) on broadening of the pulse spectrum are presented,and the best amplitude and phase noise performance with a specific fiber length is o...     

Bendable bulk metallic glass: Effects of a thin,adhesive, strong,and ductile coating

We demonstrate, for the first time, that a thin, strong, ductile, and adhesive coating renders bulk metallic glasses (BMGs) bendable. The bending ductility of 3 mm thick BMGs, Zr₅₀Cu₃₀Al₁₀Ni₁₀ in this case, can be dramatically enhanced from ～0% to ～13.7% by the deposition of a thin bilayer film on the tensile side of the BMG sample. The bilayer, consisting of a 25 nm thick Ti adhesive layer with a 200 nm thick metallic glass (MG) overlayer, exhibits the required synergistic combination of good adhesion, high strength, and ductility compared with other single-layer films examined (Ti, TiN, and MG). Cross-sectional scanning and transmission electron microscopy, together with finite element modeling, reveal that the bilayer coating absorbs deformation while allowing more homogeneous formation of a high density of smaller shear bands at the bilayer/BMG interface. The bilayer coating, in turn, covers surface weak points and minimizes the formation of localized shear bands which lead to catastrophic failure under bending. As a result, the average shear-band spacing in bilayer-coated BMGs is small, 54 μm, and approximately equal to that found in bendable, 450 μm thick, MG ribbons. Thus, coated BMGs can accommodate large strains and overcome the MG size effect, without sacrificing their extraordinary mechanical properties. Our results for both coated and uncoated BMGs, as well as previously reported results for uncoated metallic glasses, with thicknesses ranging from ribbons to thin plates to bulk, are well described by a simple power law relationship between plastic strain to failure and shear band spacing. This scaling law may be useful in guiding future experiments toward producing more flexible BMGs.     

Dose-dependent gingival overgrowth induced by cyclosporin in rats

This study evaluated the effect of dosage on severity of cyclosporin-A (CSA) induced gingival overgrowth. Eighty (80) male Sprague-Dawley rats were randomly distributed into 4 groups. Rats in each group daily received CSA in mineral oil by gastric feeding at dosages of 0 (control), 3, 10, and 30 mg/kg, respectively, for 6 weeks. Stone models of the mandibular incisal region were obtained biweekly and were used for analysis of the gingival dimensions. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluations. Animals were sacrificed at the end of week 6 and tissue sections were processed for histopathologic evaluation Gingival overgrowth including bucco-lingual and mesio-distal width and vertical height were significantly increased with increasing CSA dosage. Furthermore, the gingival dimensions displayed a positive linear relation to dosage and treatment duration. The histopathologic evaluation revealed a granulomatous tissue wedging the tooth-gingival interface in the 3 mg/kg group. This tissue had reached exuberant size in the 10 and 30 mg/kg groups. In summary, the analysis of gingival dimensions the histopathologic evaluation shows a dose-dependent effect on the severity of CSA-induced gingival overgrowth.     

Unloading yield effects in aluminum alloys

A yield effect produced by unloading and reloading during tensile deformation has been observed for several heat treated aluminum alloys. The effect depends on the composition and heat treatment of the material, as well as on the strain (or stress) at which the unloading takes place. Although the effect is independent of the unloading time at room temperature, it is found to be time dependent at 200 K where diffusion of solute elements in aluminum is sluggish. A qualitative model based on the shearing of coherent precipitates during deformation and subsequent healing of the precipitates by rapid short range diffusion in the unloaded state is proposed to explain the effect.     

Nickel silicidation techniques for strained Si1?xGex, Si1?x?yGexCy, and Si1?yCy alloys material-device applications

A nickel silicide process for Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 μΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloys. The technique is promising for Si or Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.     

The effects of doping impurities and substrate crystallin on the formation of nickel suicides on silicon at 200–280° C

Transmission electron microscopy and Auger electron spectroscopy have been applied to investigate the effects of doping impurities and substrate crystallinity on the formation of nickel suicides at 200–280° C in nickel thin films on silicon. The systems investigated included samples with as-implanted BF₂, B, F, As, and P and recrystallized (001) Si as well as P-doped low pressure chemical vapor deposited (LP-P) and B-doped plasma enhanced chemical vapor deposited (PE-B) amorphous silicon substrates. In samples annealed at 220–280° C, substantial amounts of epitaxial NiSi₂ were found to form on crystalline structure of BF₂, B and F implanted samples to various extents at different temperatures. High resolution lattice imagings of cross-sectional samples showed that the epitaxial NiSi₂/Si interfaces are coherent. No NiSi₂ was detected in all nickel thin films deposited on implantation-amorphous specimens. NiSi₂ epitaxy was found to be a sensitive function of annealing temperature. Good correlation was found between the atomic size factor and resulting stress and NiSi₂ epitaxy at low temperature. The formation of Ni₂Si and NiSi was observed to be influenced by the dopant species and crystallinity of the substrates. The vast difference in inducing the formation of nickel suicides in implantation-amorphous and recrystallized samples is likely due to variations in initial structure and/or dopant distribution. The finding that bothn-type andp-type dopants influenced the formation of Ni₂Si and NiSi suggested that they may be related to the electrical activity of the doping species in recrystallized samples. NiSi, possessing one of the lowest resistivity among all metal silicides, was found to be the only phase formed in all implantation-amorphous as well as LP-P and PE-B amorphous silicon samples annealed at 280° C. Nickel thin film appears to be an attractive candidate for the metallization of amorphous silicon devices.