CXMS study of mild steel laser alloyed with CrB2

Laser alloying of surfaces has attracted a great deal of attention for technical applications. By laser alloying of materials it is possible to improve hardness as well as wear and corrosion resistance of the surface without affecting the bulk material. The surface of a mild steel (C45) substrate was laser-alloyed with chromium-boride CrB₂. The chromium-boride was added to the substrate surface by powder injection during laser surface melting with a high power continuous-wave CO₂-laser. The resulting surface layers were studied by surface Mössbauer measurements. The backscattering geometry of Conversion X-ray Mössbauer Spectroscopy (CXMS) was used to study the phase formation in the laser alloyed surface. The results for the treated surfaces are discussed for different samples.     

Adsorption of ammonia on treated stainless steel and polymer surfaces

Adsorption of dynamically diluted ammonia at part-per-billion to low part-per-million concentrations in dry nitrogen was studied with treated and non-treated stainless steel and polymer test tubes. The treatments included electropolishing and two types of coatings based on amorphous silicon. Cavity ring-down spectroscopy with an external cavity diode laser operating in the near-infrared wavelength range was used to monitor the adsorption process in real time in continuous-flow conditions to obtain quantitative assessment of the adsorptive properties of the studied surfaces. The investigated polymers were all less adsorptive than any of the treated or non-treated stainless steel surfaces. Some of the commercial coatings reduced the adsorption loss of stainless steel by a factor of ten or more. Polyvinylidene fluoride was found to be superior (less adsorption) to the four other studied polymer coatings. The number of adsorbed ammonia molecules per surface area obtained at different ammonia gas phase concentrations was modeled with Langmuir and Freundlich isotherms. The time behavior of the adsorption–desorption process occurring in the time scale of seconds and minutes was simulated with a simple kinetic model.     

Microstructure and corrosion behavior of austenitic stainless steel treated with laser

Surface modification of AISI316 stainless steel by laser melting was investigated experimentally using 2 and 4 kW laser power emitted from a continuous wave CO₂ laser at different specimen scanning speeds ranged from 300 to 1500 mm/min. Also, an investigation is reported of the introduction of carbon into the same material by means of laser surface alloying, which involves pre-coating the specimen surfaces with graphite powder followed by laser melting. The aim of these treatments is to enhance corrosion resistance by the rapid solidification associated with laser melting and also to increase surface hardness without affecting the bulk properties by increasing the carbon concentration near the surface. Different metallurgical techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the treated zone. The microstructures of the laser melted zones exhibited a dendritic morphology with a very fine scale with a slight increase in hardness from 200 to 230 Hv. However, the laser alloyed samples with carbon showed microstructure consisting of γ dendrite surrounded by a network of eutectic structures (γ+carbide). A significant increase in hardness from 200 to 500 Hv is obtained. Corrosion resistance was improved after laser melting, especially in the samples processed at high laser power (4 kW). There was shift in I_corr and E_corr toward more noble values and a lower passive current density than that of the untreated materials. These improvements in corrosion resistance were attributed to the fine and homogeneous dendritic structure, which was found throughout the melted zones. The corrosion resistance of the carburized sample was lower than the laser melted sample.     

Thermal hydraulic characterization of stainless steel wicks for heat pipe applications

Heat pipe design and manufacturing require the knowledge of the thermal hydraulic performance of the wicks. The aim of the present work is the thermal hydraulic characterization of stainless steel wicks (sintered porous media and gauzes) to be employed in our experimental water heat pipe. Commercial sintered porous media (able to capture 90 % of 90 μm particles and 99.9 % of 130 μm particles) and gauzes (nominal wire size 0.11 mm, square mesh opening 0.209 mm) have been used. Thermal hydraulic characterization of the wicks is obtained through the experimental measurement of: capillary height (through which the equivalent porous radius can be evaluated), liquid hydraulic head (through which the liquid pressure drop in the wick is evaluated) wick permeability is also evaluated from the hydraulic head (through Darcy's law), heat flux, wick mass flow rate during the evaporation (through which, from the knowledge of other measured wick parameters, the wick two-phase pressure drop is calculated) and wick porosity (through which the thermal conductivity of the wick saturated with liquid can be determined). Concerning the heat flux, it is found to be dependent on the distance between the liquid level and the evaporating zone, the evaporating zone length, the wall superheat and the water subcooling, the contact between the heater and the wick and the superficial boundary conditions of the wick.     

CEMS,CXMS and X-ray investigation of the microstructure of the surface layer in plasma nitrocarburized steel

The microstructure of the compound layer formed by plasma nitrocarburizing of steels has been investigated by means of conversion electron, conversion X-ray Mössbauer spectroscopy (CEMS, CXMS) and X-ray diffraction. A carbon steel C35 was plasma nitrocarburized using a gas mixture of nitrogen, hydrogen and methane. The compound layer was mechanically removed in steps, followed by Mössbauer and X-ray investigations. It was found that this layer consists of different nitrides and carbides. Their concentrations vary with the depth below the surface.     

The effect of ultrasonic processing on solidification microstructure and heat transfer in stainless steel melt

The heat transfer in the ultrasonic processing of stainless steel melt is studied in this thesis. The temperature field is simulated when the metal melt is treated with and without ultrasound. In order to avoid the erosion of high temperature melt, ultrasound was introduced from the bottom of melt. It is found that the temperature of melt apparently increases when processed with ultrasound, and the greater the ultrasonic power is, the higher the melt temperature will be; ultrasonic processing can reduce the temperature gradient, leading to more uniform temperature distribution in the melt. The solidification speed is obviously brought down due to the introduction of ultrasound during solidification, with the increasing of ultrasonic power, the melt temperature rises and the solidification speed decreases; as without ultrasound, the interface of solid and mushy zone is arc-shaped, so is the interface of liquid and mushy zone, with ultrasound, the interface of solid and mushy zone is still arc-shaped, but the interface of liquid and mushy zone is almost flat. The simulation results of temperature field are verified in experiment, which also indicates that the dendrite growth direction is in accord with thermal flux direction. The effect of ultrasonic treatment, which improves with the increase of treating power, is in a limited area due to the attenuation of ultrasound.     

Multicyclic fatigue of stainless steel treated by a high-intensity electron beam: surface layer structure

It is shown that an electron-beam treatment of the 08X18H10T steel specimens under the condition of melting of the ~5 μm surface layer (electron beam energy density 25 J/cm²) increases their fatigue life by a factor of 3.5. The structural-phase states and defect substructure of this steel are studied by the methods of optical, scanning and transmission electron microscopy, and the factors responsible for its increased fatigue life are revealed.     

Comparison of fractal analyses methods and fractal dimension for pre-treated stainless steel surfaces and the correlation to adhesive joint strength

The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (≈0.5–100 μm). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, R_a, but only weakly to the fractal dimension. Hence, traditional parameters, such as R_a, tell us very little about the spatial distribution of the elevation data. Received: 22 December 1999 / Accepted: 9 October 2000 / Published online: 9 February 2001     

XRD and XPS analysis of laser treated vanadium oxide thin films

In this work, we present X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis of laser treated vanadium oxide sols. The films were also observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to reveal how the original xerogel structure changes into irregular shaped, layer structured V₂O₅ due to the laser radiation. XRD revealed that above 102 W/cm² the original xerogel structure disappears and above 129 W/cm² the films become totally polycrystalline with an orthorhombic structure. XPS spectra showed O/V ratio increment by using higher laser intensities.     

Initial oxidation of duplex stainless steel

Three different techniques were used to produce thin oxide layers on polished and sputter-cleaned duplex stainless-steel samples. These samples were exposed to 10⁻⁵ mbar of pure oxygen inside the vacuum chamber, exposed to ambient conditions for 24 h, and plasma oxidized. The oxide layers thus produced were analysed using XPS depth profiling in order to determine the oxide layers’ compositions with depth. We found that all the techniques produce oxide layers with different traces of metallic components and with the maximum concentration of chromium oxide shifted towards the oxide-layer-bulk-metal interface. A common characteristic of all the oxide layers investigated is a double-oxide stratification, with regions closer to the surface exhibiting higher concentrations of iron oxide and those more in-depth exhibiting higher concentrations of chromium oxide. A simple non-destructive Thickogram procedure was used to corroborate the thickness estimates for the thinnest oxide layers.     

A phase-field modeling of void swelling in the Austenitic stainless steel

Two-dimensional phase-field simulations of void swelling in the Austenitic stainless steel were performed for irradiated materials. A numerical model was established for void swelling with an implementation of the elasticity effect, and we examined the roles of the applied stress and grain boundary sink strength and Frenkel defect recombination in determining the void swelling rate. The obtained results were compared with the existing experimental observations.     

Characterization of silane layers on modified stainless steel surfaces and related stainless steel-plastic hybrids

The aim of this work was to characterize silane layers on the modified stainless steel surfaces and relate it to the adhesion in the injection-molded thermoplastic urethane-stainless steel hybrids. The silane layers were characterized with scanning electron microscope and transmission electron microscope, allowing the direct quantization of silane layer thickness and its variation. The surface topographies were characterized with atomic force microscope and chemical analyses were performed with X-ray photoelectron spectroscopy. The mechanical strength of the respective stainless steel-thermoplastic urethane hybrids was determined by peel test. Polishing and oxidation treatment of the steel surface improved the silane layer uniformity compared to the industrially pickled surface and increased the adhesion strength of the hybrids, resulting mainly cohesive failure in TPU. XPS analysis indicated that the improved silane bonding to the modified steel surface was due to clean Fe₂O₃-type surface oxide and stronger interaction with TPU was due to more amino species on the silane layer surface compared to the cleaned, industrially pickled surface. Silane layer thickness affected failure type of the hybrids, with a thick silane layer the hybrids failed mainly in the silane layer and with a thinner layer cohesively in plastic.     

Fiber laser micro-cutting of stainless steel sheets

The authors report on laser micro-cutting results for stainless steel foils with the aid of a 100 W fiber laser. This novel laser source combines a high output power in relation to conventional laser sources for micro-processing applications with an excellent beam quality (M²=1.1). Different material thicknesses were evaluated (100 μm to 300 μm). Processing was carried out with cw operation of the laser source, and with nitrogen and oxygen as assisting gases. Besides the high processing rate of oxygen assisted cutting, a better cutting performance in terms of a lower kerf width was obtained. PACS 42.82.Cr; 42.62.Cf; 81.05.Bx     

Micro-hot-embossing of 316L stainless steel micro-structures

In this paper, the fabrication of an array of 316L stainless steel cylindrical micro-structures by hot-embossing is studied. The effects of various embossing parameters on the filling of the micro-cavities of silicon mold insert and the demolding of micro-structures are investigated. They include different silicon mold insert configurations, embossing pressure, embossing temperature, embossing time and the thickness of embossing substrate on which the micro-structures stand. Two types of silicon mold insert configurations are investigated. Hot-embossing study with the silicon mold insert attached on the upper mold plate shows that it is not feasible to achieve complete filling. Incomplete filling occurs and increasing the embossing pressure causes excessive thinning of the embossing substrate, so that micro-structures are torn off during demolding. Experiments show that the configuration that the silicon mold insert is positioned flush with lower mold surface improves complete filling. Using suitable embossing pressure and temperature, the larger substrate thickness and longer embossing time ensure the fabrication of defect-free fully filled micro-structures.     

焊后热处理对聚变堆用奥氏体不锈钢MAG焊焊缝金属冲击韧性的影响

对聚变堆用316LN奥氏体不锈钢熔化极活性气体保护电弧焊(MAG焊)接接头进行不同温度的热处理,并在液氮温度下进行夏比冲击试验。利用光学显微镜、扫描电镜、EDS分析等研究了热处理温度对接头微观组织、断口形貌及析出物的影响。结果表明,873K热处理可以显著提高焊缝金属冲击韧性,但随着热处理温度的上升,焊缝金属逐渐出现沿着晶界分布的析出物,韧性逐渐下降。断口均为延性断裂,但随着热处理温度的升高,韧窝变浅、数量变少。韧窝底部存在球状析出和不规则状析出,球状析出在焊接过程中产生,不因热处理温度而变化,不规则析出随着热处理温度的升高逐渐增多。焊材中的Mo含量过高导致焊缝金属中Mo在晶界大量偏聚,促进了σ相的析出,当σ相在晶界形成连续分布后,焊缝金属冲击韧性显著下降。     

Microstructure of single crystals of austenitic stainless steel

Auger spectroscopy and x-ray structure analysis have been used to study the chemical and phase inhomogeneity in single crystals of the austenitic nitrided stainless steel Cr22Ni17Mo3 with various morphologies of the dendritic structure. In single crystals grown in the 100 direction with a classical dendritic structure the interaxial regions are highly enriched with S, N, and C and weakly enriched with Mo, V, and Mn. At the same time these regions have a high density of particles of the type Me₂₃C₆, Me₇C₃, and vanadium carbonitrides, oriented in the growth direction. The axial regions have a subcellular structure, with oxygen-rich subcell boundaries. In single crystals with growth direction close to 110, in which only secondary dendrite axes are formed, the alloying elements, impurities, and second-phase particles are distributed relatively uniformly throughout the ingot.V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–6, October, 1992.     

Thin films of ZnTe electrodeposited on stainless steel

The electrodeposition of zinc telluride (ZnTe) thin films on stainless steel foil substrates from an aqueous solution containing ZnSO₄ (150 mM) and TeO₂ (0.5 mM) is performed. For the deposition of stoichiometric films at a bath temperature 80 °C and pH=3.5, the suitable deposition potential is found to be in the range -740 mV to -800 mV against a Ag/AgCl reference electrode. The films structure, surface morphology, chemical composition, optical absorption coefficient, bandgap energy and electrical resistivity are measured and the results are discussed. Films are composed of small crystallites, and their surface texture, which depends on the film stoichiometry, varies with the deposition potential. Films have a resistivity greater than 10⁹ cm and a bandgap energy that is measured in the range 2.1 to 2.3 eV. Films annealed in nitrogen for 15 min and at 350 °C show p-type conductivity. PACS 81.15.Pq; 78.66.Hf; 68.55.Jk; 73.61.Ga     

Laser drilling of stainless steel with nanosecond double-pulse

Nanosecond double-pulse laser drilling is reported in this paper. The double-pulse herein represents two closely conjoint pulses with 21 ns pulse duration and about 52 ns interpulse separation, which are acquired by temporal pulse shaping. Percussion drilling with such double-pulse is performed in stainless steel samples with different laser fluences, sample's thickness, repetition rates and ambient pressures. The experimental results show that the drilling rates of double-pulse drilling are more than one order of magnitude higher than that of conventional single-pulse drilling in air. Differences in the processing results between single-pulse and double-pulse with various processing parameters are investigated. In addition the ablation mechanisms of the double-pulse drilling are discussed.     

Behavior of hydrogen in stainless steel under irradiation

A nondestructive method of the simultaneous analysis of hydrogen and helium in combination with the technique of studying hydrogen migration provides fundamentally new information about the hydrogen behavior in metal-hydrogen systems: about hydrogen migration in metals directly under irradiation and about the mutual effect of implanted hydrogen and helium in constructional materials of nuclear and thermonuclear reactors. The irradiation of metals and alloys with ionizing radiation (ion beams, electrons, and x-ray quanta) causes intense hydrogen migration due to the excitation of electron states from metal-hydrogen bonds whose lifetime is sufficient for hydrogen to leave its regular positions and for nonequilibrium migration. Hydrogen migration over and escape from metals and alloys under the action of electrons and x-ray quanta with an energy below the threshold of defect formation are accompanied by the rearrangement of the defect structure of the material: the annealing of defects of the hydrogen origin due to the annihilation of defects (interstitial atoms and hydrogen-free vacancies). Hydrogen dissolved in metals and alloys reduces the trapping coefficient of the implanted helium, which is due to the formation of fine complexes HV and HV₂ and, as a result, to a decrease in the probability of formation of large vacancy complexes which are effective traps for helium.