Influence of modification time and high frequency ultrasound irradiation on self-assembling of alkylphosphonic acids on stainless steel: Electrochemical and spectroscopic studies

Self-assembly of alkylphosphonic acids on stainless steel was investigated under different conditions. Four different alkylphosphonic acids exhibiting alkyl chain of various size were synthesized and studied: butylphosphonic acid (C4P), octylphosphonic acid (C8P), decylphosphonic acid (C10P), and hexadecylphosphonic acid (C16P). Electrochemistry experiments were extensively carried out in order to determine electrochemical surface blocking of adsorbed layers in function of grafting time. In term of surface blocking, an 8 h modification time was optimal for all alkylphosphonic acids. Longer immersion times lead to degradation of adsorbed layers. For the first time, grafting of C16P was studied under high frequency ultrasound irradiation. Interestingly, grafting process is highly accelerated under sonication and well-covering C16P modified substrates are obtained after 1 h of immersion under ultrasound irradiation. This would allow to elaborate high-quality alkylphosphonic acids modified samples within much shorter times. Water contact angles measurements and X-ray Photoelectrons Spectroscopy (XPS) confirmed presence of adsorbed alkylphosphonic acids on stainless steel surface. A very tight link between electrochemical blocking, surface hydrophobicity and species chemical grafting was established.     

Morphological and structural characterizations of different oxides formed on the stainless steel by Nd:YAG pulsed laser irradiation

The effects of laser surface irradiation on microstructure of AISI 304 stainless steel were investigated. The stainless steel surface was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). XRD patterns indicated that different oxides, such as chromium oxides and manganese oxides were fabricated successfully on the surface of the stainless steel by Nd:YAG pulsed laser irradiation. The effects of the growth conditions such as the laser power density on the morphologies of the different oxides have been investigated. From the FESEM, EDS (energy-dispersive spectrum) and TEM observations, the oxides with triangle-like, quadrangular and hexagonal morphologies have been fabricated successfully. The XPS was used to verify the formed oxides which had been detected by the XRD patterns. It was considered that laser power density had a critical role in the formation of different oxides.     

质子辐照不锈钢中氢气泡产生和演化研究

采用质子辐照模拟方法和正电子湮没寿命测量方法研究了质子辐照在国产改进型316L不锈钢中产生的氢气泡及其随辐照质子注量的演化过程。5×10^12,5×10^13,5×10^14／cm^2质子辐照的实验结果表明,辐照在不锈钢中产生氢气泡的尺度随辐照质子注量增加而增大,在质子注量为5×10^14／cm^2时氢气泡尺寸达到0．62nm,气泡的浓度随质子注量增加而减小。The bubble production and evolution in the home-made modified 316L stainless steel have been investigated by the proton irradiation simulation technique and the positron annihilation lifetime measurement. The experimental results of 5 × 10^12, 5 × 10^13 and 5 × 10^14/cm^2 proton irradiations show that the produced bubble size increases, while the bubble concentration decreases, with the increasing of the irradiation proton flueence. At the proton irradiation fluence of 5 × 10^14/cm^2 the bubble size reaches 0.62 nm.     

Selective role of bainitic lath boundary in influencing slip systems and consequent deformation mechanisms and delamination in high-strength low-alloy steel

We elucidate here the deformation behaviour and delamination phenomenon in a high-strength low-alloy bainitic steel, in terms of microstructure, texture and stress evolution during deformation via in situ electron back-scattered diffraction and electron microscopy. Furthermore, the selective role of bainitic lath boundary on slip systems was studied in terms of dislocation pile-up and grain boundary energy models. During tensile deformation, the texture evolution was concentrated at {1 1 0}<1 1 1> and the laths were turn parallel to loading direction. The determining role of lath on the deformation behaviour is governed by length/thickness (l/t) ratio. When l/t > 28, the strain accommodates along the bainite lath rather than along the normal direction. The delamination crack initiated normal to (0 1 1) plane, and become inclined to (0 1 1) plane with continued strain along (0 1 1) plane and lath plane. This indicated that the delamination is not brittle process but plastic process. The lack of dimples at the delaminated surface is because of lack of strain normal to the direction of lath. The delaminated (0 1 1) planes were associated with cleavage along the (1 0 0) plane.     

Dual beam method for laser welding of galvanized steel: Experimentation and prospects

Laser welding of zinc-coated steel sheets in lap configuration poses a challenging problem, because of the zinc vapours spoiling the quality of the weld. In continuation to the earlier work, the novel solution of dual laser beam method for lap welding of galvanized steel sheets is discussed here in view of the recently obtained observations and ensuing concerns. In this method the precursor beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The metallurgical analysis of the welds is encouraging showing absence of zinc in the welded area. In the current work on this technique, new experimental results have been obtained verifying the earlier observations. Along with this, the possibility of using a transversely split-up beam for the welding purposes with this approach is discussed and analyzed in this paper. This new technique is expected to be very useful in prospective industrial applications requiring higher welding throughput along with the needed quality.     

Densification behavior of gas and water atomized 316L stainless steel powder during selective laser melting

The densification during selective laser melting (SLM) process is an important factor determining the final application of SLM-part. In the present work, the densifications under different processing conditions were investigated and the densification mechanisms were elucidated. It was found that the higher laser power, lower scan speed, narrower hatch spacing and thinner layer thickness could enable a much smoother melting surface and consequently a higher densification.The gas atomized powder possessed better densification than water atomized powder, due to the lower oxygen content and higher packing density of gas atomized powder. A large number of regular-shaped pores can be generated at a wider hatch spacing, even if the scanning track is continuous and wetted very well. The densification mechanisms were addressed and the methods for building dense metal parts were also proposed as follows: inhibiting the balling phenomenon, increasing the overlap ratio of scanning tracks and reducing the micro-cracks.     

Raman identification of corrosion products on automotive galvanized steel sheets

Iron oxides (haematite, maghemite, magnetite), (oxy)hydroxides (lepidocrocite), carbonates, as well as zinc carbonate and oxide, have been identified on corroded galvanized steel samples after corrosion accelerating tests in the laboratory and compared with those observed on samples taken from vehicles that have been in circulation for five years in severe weather conditions. Spectra recorded on the corroded parts are compared with synthesized compounds. (Hydroxy)carbonates are clearly evidenced on galvanized and phosphated steel sheets. Corrosion layers beneath the paint could be detected. White regions always correspond to a ZnO‐rich phase but maghemite (γ‐Fe₂O₃) and sometimes akaganite (β‐FeOOHCl) are observed at the centre (maroon) of very corroded spots. Maghemite is observed in strongly corroded regions. Goethite (α‐) and lepidocrocite (γ‐FeOOH) (and akaganite) are observed at the surface of less corroded regions of phosphate‐free galvanized steel and are absent for phosphate‐coated steel. Green rust is observed only on galvanized samples corroded in the laboratory. Copyright © 2008 John Wiley & Sons, Ltd.     

光纤传能的移动式激光诱导击穿光谱钢铁快速检测与分类

为了实现工业现场对特种钢材的快速检测与种类识别,采用基于光纤传能的移动式激光诱导击穿光谱(LIBS)样机对14种特种钢材进行光谱数据的采集与分析,采用预选谱线并遍历组合的降维方法与支持向量机(SVM)相结合的算法对特钢材料的光谱进行快速分类.分别将原始光谱数据、归一化处理后的光谱数据、归一化处理+遍历组合优选谱线数据作...     

Principle of massive support in the opposed anvil high pressure apparatus

The Bridgman anvil technique offers a simple and versatile means of generating very high pressures required in solid state studies. The opposed anvil technique is based on the principle of massive support. The practical case of a gasketted anvil is considered, and an expression for the maximum pressure generated under massive support is derived in terms of the geometric parameters, the strength of the anvil material and the gasket properties. In particular, for a given maximum pressure, it is possible to calculate the taper angle, the taper height and the gasket thickness from this expression. The anvil is assumed to be in the elastic region under load. Good agreement is obtained between the calculated and the experimental values for the massive support factor (msf) for various taper angles. By choosing the proper geometry, it is possible to achieve a pressure as high as 130 kbar in an alloy steel anvil. It has been clearly found that the straight portion, where the taper ends, does not really take any part in changing the stress pattern. Thus the minimum straight portion can serve the purpose, and will result in material saving. Anvils exhibit yielding at very high pressure. It is also pointed out that a further strengthening of the anvil can extend the ultimate pressure. Several methods of further strengthening the anvils are discussed.     

Structure and properties of laser quenched 4Cr13 steel

The structure and properties of laser quenched 4Cr13 steel were reported. The results show that: (1) Fine martensite is obtained after laser quenching. The highest content of retained austenite in the surface area 10 μm thick of laser hardened zone is 47. 13 percent, but only 3.6 percent of retained austenite is measured inside the laser hardened layer after the surface layer 10μm thick is worn off. (2) The hardness of laser quenched layer is much higher (HV_(0.1) 690) than that of the substrate (HV_(0.1) 237). (3) The wear resistance of laser quenched layer is 3.3 times higher than that of traditionally treated specimen and the corrosion resistance of 4Cr13 steel is also improved greatly by laser quenching.