Laser-induced reaction of Si powder with a steel substrate

We have determined the phase composition and microhardness of coatings produced by the laser melting of silicon powder on the surface of steel substrates. Laser exposure leads to the formation of iron silicides on the substrate surface. The iron content of the silicides depends on the effective laser power and increases from that of FeSi₂ to Fe_0.9Si_0.1. The coatings have the highest microhardness at an effective power of ≏ 400 W s/m, which corresponds to the highest FeSi content.     

Microstructure and properties of composite (B + C) diffusion layers on low-carbon steel

Combined surface hardening with boron and carbon was used for low-carbon 5120 steel. The microstructure, carbon profiles and chosen properties of borided layers produced on the carburized 5120 steel have been examined. These composite (B + C) layers are termed borocarburized layers. The microhardness profiles and wear resistance of these layers have been studied. In the microstructure of the borocarburized layer two zones have been observed: iron borides (FeB + Fe₂B) and a carburized layer. It has been found the depth (100–125 m) and microhardness (1500–1900 HV) of iron borides zone. The carbon content (0.83–1.46 wt pct) and microhardness (950 HV) beneath iron borides zone have been determined. The microhardness gradient in borocarburized layer has been reduced in comparison with the only borided layer. An increase of distance from the surface is accompanied by a decrease of carbon content and microhardness in the carburized zone. The carbon and microhardness profiles of borided, carburized and borocarburized layers have been presented. A positive influence of composite layers (B + C) on the wear resistance was determined. The wear resistance of the borocarburized layer was determined to be greater in comparison with that for only borided or only carburized layers.     

Solid phase reactions between Fe thin films and Si-Ge layers on Si

Solid phase reactions in Fe thin films on epi-Si_0.8Ge_0.2, poly-Si_0.7Ge_0.3, a-Si_0.8Ge_0.2, and a-Si_0.7Ge_0.3 layers on silicon have been investigated. The as-deposited samples were in situ annealed in the ultrahigh vacuum chamber at 400-800 °C for 30 min. The island structure was found to cause the abrupt increase in the sheet resistance of the annealed Fe/SiGe samples at 700-800 °C. The formation of FeSi islands containing a small amount of Ge is attributed to the preferential reactions of Fe with Si to Ge. As the annealing temperature was raised to 800 °C, the Fe(Si_1−xGe_x) phase is the only phase found in the annealed Fe/epi-Si_0.8Ge_0.2 and Fe/poly-Si_0.7Ge_0.3 samples. On the other hand, at the annealing temperature above 700 °C, the β-Fe(Si_1−xGe_x)₂ phase was observed in the annealed Fe/a-Si_0.8Ge_0.2 and Fe/a-Si_0.7Ge_0.3 but the Fe(Si_1−xGe_x) is still the dominant phase. The results indicate that the formation of Fe disilicide was retarded by the presence of Ge atoms.     

Carbon layers formed on steel and Ti alloys after ion implantation of C+ at very high doses

Ion implantation is a useful technique to tailor surface properties of steel and Ti alloys. In particular, very high dose C⁺ implantation (in the range of 10¹⁸ ions cm⁻²) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation of carbon doses up to 8×10¹⁸ ions cm⁻² has been performed on 440C martensitic stainless steel and Ti6Al4V substrates under similar conditions and tribological and surface analysis results have been compared. Surface hardening occurred for all ion implantation conditions up to doses of 10¹⁸ ions cm⁻²1, 2, 3. Higher doses resulted in a different behaviour for both materials. The stainless steel showed a softening while a twofold hardness increase was maintained in the Ti alloy. Nevertheless, at the higher implanted dose a decrease in hardness was also observed in the Ti alloy. Small area XPS analyses were performed to evaluate the chemical states after ion implantation and establish a relationship with the observed surface hardening. Depth profile XPS analyses showed that for a dose of 4×10¹⁸ ions cm⁻² a carbon layer (with concentration over 85% at. C) was formed in the near surface region for both materials.     

Hydrogen permeation in Fe40Ni38B18Mo4 and Fe81B13.5Si3.5C2 amorphous alloys

Hydrogen permeation in Fe₄₀Ni₃₈B₁₈Mo₄ and Fe₈₁B_13.5Si_3.5C₂ amorphous alloys was evaluated using electrochemical permeation measurement in this study. Due to the different alloying elements in these alloys, higher hydrogen permeation rate and effective diffusivity, and lower apparent solubility in Fe₄₀Ni₃₈B₁₈Mo₄, amorphous alloys were detected. In this study, the behavior of hydrogen permeation affected by the alloying elements of carbon, silicon, and boron in iron-based amorphous alloys was also described.     

Acid-base reactions in fused alkali borate + TiO2 mixtures

The nature of the titanium-containing phases which crystallize from solutions of TiO₂ in fused alkali metal borates, varies with the alkali cation, the mole ratio of alkali oxide to B₂O₃, and the initial concentration of TiO₂. Recrystallization of TiO₂ rather than crystallization of complex titanates, is enhanced by the presence in solution of small cations, by a high proportion of B₂O₃ relative to alkali oxide, and by higher concentrations of TiO₂.The crystallization of complex titanates is correlated with the formation of borate groups containing non-bridging oxygens whose existence has been suggested by previous workers.     

Microstructure and mechanical properties of a three-layer B4C/Al–B4C/TiB2–B4C composite

A three-layer structure material, consisting of B₄C/Al, B₄C/TiB₂ and B₄C composites, was obtained using a two-step method for both hot pressing and aluminum infiltration in vacuum. The three-layer B₄C/Al–B₄C/TiB₂–B₄C composite showed good interfacial bonding. Before aluminum infiltration the B₄C porous layer in the three-layer preform looked like a three-dimensional network of interconnected capillaries. The microstructures of both B₄C/TiB₂ and B₄C layers showed no apparent changes before and/or after aluminum infiltration. The three-layer composite showed improved fracture toughness than that of B₄C material and higher comprehensive hardness than that of B₄C/Al material.     

基片及基片温度对Fe4N薄膜的形成及其特性的影响

以双离子束溅射法在（111）硅片和玻璃上分别制得了单－γ′－Fe4N薄膜，研究了基片及基片温度对薄膜的结构和磁性能的影响，结果表明，（111）硅片为基片，可制得无晶粒择优取向的单一γ′－Fe4N相；而以玻璃为基片，在基片温度为160℃时，则可制得具有（100）面晶粒取向的单一γ′－Fe4N相薄膜，与无晶粒择优取向的γ′－Fe4N相比较，具有（100）面晶粒取向的γ′－Fe4N相的矫顽力较低，易达到磁饱和，但二者的饱和磁化强度基本一致。     

Properties of B4C/Al–B4C composite with a two-layer structure

In order to obtain a material with a promising bulletproof performance, a two-layer structure composite consisting of B₄C/Al-B₄C was obtained using a two-step method for both hot pressing and infiltration aluminum in vacuum. Before aluminum infiltration the B₄C porous layer of the two-layer preform looked like a three-dimensional network of interconnected capillaries. For the B₄C ceramics layer the microstructure showed no apparent change before and/or after aluminum infiltration. The two-layer composite showed improved fracture toughness than that of B₄C material and higher comprehensive hardness than that of B₄C-Al material.     

Photoacoustic properties of softmagnetic amorphous Fe81B13Si4C2 ribbon

Photoacoustic properties of amorphous Fe81B13Si4C2 ribbons were investigated. The amplitude and phase photoacoustic spectra were measured as a function of the modulation frequency of an He–Ne laser beam. Thermal diffusivity was determined by comparison of obtained experimental results and calculated theoretical photoacoustic spectra for a non-annealed Fe81B13Si4C2 sample and an Fe81B13Si4C2 sample annealed at 600 °C. © 1998 Chapman & Hall     

Phase Composition of the Products of Fe Oxidation in Fe + C + NaCl + H2O + O2 Exothermic Mixtures

Using thermodynamic analysis of the Fe–C–NaCl–H₂O–O₂ system and experimental studies (x-ray diffraction and Mössbauer spectroscopy) of exothermic mixtures containing Fe metal, activated carbon, water, and NaCl, we identified the state of Fe and determined the phase composition of the reaction products at different stages of oxidation with atmospheric oxygen. The calculation and experimental results are in reasonable agreement. Under the conditions of restricted access for air, the main oxidation product is magnetite, Fe₃O₄. Free access for air leads to the formation of hydrous ferric oxide, Fe₂O₃ · nH₂O. The most stable phase under the conditions of interest is goethite, Fe₂O₃ · H₂O (-FeOOH). Storage of incompletely oxidized samples away from air for 7–14 days leads to partial reduction of iron(III) oxide phases to Fe₃O₄ and -Fe.     

Fe+Ni+C体系合成粗颗粒金刚石单晶的生长特征

在配备有高精密化控制系统SPD6×1670T型国产六面顶压机上,采用Fe80Ni20粉末触媒和高纯石墨开展粗颗粒金刚石单晶的生长特征研究。在粉末触媒技术合成金刚石的基础上,引入旁热式组装,以及采用优选粒度的触媒,特别是通过优化合成工艺严格地控制了合成腔体内晶体的成核量及生长速度。最终,在高温高压条件下(约5.4GPa、1435℃)成功合成出尺寸达到0.95mm(18/20目)的优质的粗颗粒金刚石单晶,分析了粗颗粒金刚石的生长特征和晶体缺陷,期待研究的结果有助于我国高品级粗颗粒金刚石的发展。     

Influence of B4C on the tribological and mechanical properties of Al 7075–B4C composites

In the present investigation, the influence of B₄C on the mechanical and Tribological behavior of Al 7075 composites is identified. Al 7075 particle reinforced composites were produced through casting, K₂TiF₆ added as the flux, to overcome the wetting problem between B₄C and liquid aluminium metal. The aluminium B₄C composites thus produced were subsequently subjected to T6 heat treatment. The samples of Al 7075 composites were tested for hardness, tensile, compression, flexural strengths and wear behavior. The test results showed increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B₄C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. A mechanically mixed layer containing oxygen and iron was observed on the surface, and this acted as an effective insulation layer preventing metal to metal contact. The coefficient of friction decreased with increased B₄C content and reached its minimum at 10 vol% B₄C.     

Anomalous electron-beam-induced excitation of argon in pulsed supersonic streams of Ar+CH4, Ar+SiH4, and Ar+ CH4+SiH4 mixtures

The energy exchange in supersonic streams of argon mixtures with methane and monosilane activated by an electron beam was studied. In the initial condensation stage, the stream features a selective excitation of the atomic energy levels of argon. The threshold values of parameters were determined, for which the anomalous optical emission from the electron-beam-excited mixtures is observed.     

Experimental study on buckle evolution of thin inorganic layers on a polymer substrate

In this paper the behavior of a 250 nm and a 350 nm thick Indium tin oxide (ITO) layers deposited on a 200 μm thick high temperature aromatic polyester substrate (Arylite™) and spin coated with a 3 μm silica-acrylate hybrid coating (Hard Coat) is discussed. In-situ optical microscopy of the layered structures under uniaxial compressive strain was used to determine the buckle delamination rate at different applied strains. The effect of applied uniaxial compressive strain and layer thickness on the evolution of buckle width and height was investigated. The biaxial-residual stress, uniaxial compressive stress, poor adhesion at the interface and Poisson’s ratio are believed to be responsible for the formation of telephone-cord buckling.