White etching areas (WEA) and white etching cracks (WEC) are frequently linked to premature bearing failure in conventional high carbon bearing steels like 100Cr6 (SAE 52100). In contrast, no WEA/WEC has yet been reported for the high nitrogen bearing steel X30CrMoN15-1 (SAE AMS 5898). Thus, the present study proves for the first time that X30CrMoN15-1 is also susceptible to develop WEA/WEC under rolling contact fatigue (RCF) when pre-charged with hydrogen. RCF tests conducted in parallel without hydrogen pre-charging resulted in RCF damage only, which identifies hydrogen as an active agent for WEA/WEC formation in X30CrMoN15-1. These findings correspond to the fact that hydrogen diffusion during RCF is often considered to cause or accelerate the formation of WEA/WEC. Additionally, it is observed that the M2(C, N) and M23C6 precipitates of the martensitic microstructure of the X30CrMoN15-1 do not entirely decompose during the WEA formation process as observed for M3C precipitates in 100Cr6. In conclusion, the results for X30CrMoN15-1 strongly suggest that the formation of WEA is driven by a hydrogen-activated local severe plastic deformation process, which initiates continuous dynamic recrystallisation, leading to the characteristic nano-ferritic grains observed in WEA. Also, the highly stable and self-regenerating passive chromium-oxide layer of X30CrMoN15-1 mitigates the risk of WEA/WEC failure during typical RCF operation by hindering the formation and adsorption of ionic hydrogen. Hence, this study emphasises the importance of protecting the base material against hydrogen ingress to delay WEA/WEC formation.

Abstract The impact of plasma nitriding on the microstructure and the hardness of a recently developed 4 wt.-% medium manganese steel are presented. In contrast to standard quench and tempering steels, the investigated material achieves its martensitic microstructure by air-cooling from the forging heat, which enables the reduction of the carbon footprint of the forged components. The influence of nitriding on this grade of steel has not been investigated so far, but fundamental differences in comparison to standard nitriding steels are expected due to the increased manganese concentration. To address this issue, nitriding treatments with different temperatures (350 °C, 580 °C and 650 °C) have been performed, followed by examinations of the microstructure, the phase composition, the obtained hardness profiles and the tensile properties of the bulk material after nitriding, accompanied by thermodynamic equilibrium calculations. It is demonstrated that after nitriding at 580 °C similar hardness profiles like standard nitriding steels are achieved, with a shorter process as austenitization and hardening were omitted, reaching a hardness of approximately 950 HV0.1. Furthermore, it was demonstrated that austenite can be stabilized by manganese and nitrogen partitioning to room temperature during nitriding in the intercritical phase region.

The oxygen transport membrane Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) was wetted by the reactive air brazing alloy Ag-14CuO. Triple point phases of different cobalt-copper-oxides are formed in the reaction zone and are origin of micro-cracks and stress concentration. Therefore, their identification is necessary for understanding the microstructure evolution and designing the interface structure advantageously by an adapted brazing process. However, as the cobalt-copper-oxide system can form many different oxides with solubility of Co and Cu respectively, different analytical methods are necessary for identification. TEM diffraction is used for the correct identification of the occurring crystal structures, EBSD is used for analysis of composition, arrangement and orientation of the triple point phases and EPMA is used to confirm the crystal structures identified by EBSD and to determine the elemental concentrations. As the triple point phases consist of small grains with unpredictable forms and especially, Cu-Ka can excite Co-Ka by characteristic secondary fluorescence, different evaluation procedures for EPMA are performed on FIB lamellae: 1) Approach based on standard lamellae, where FIB lamellae from standards are used to determine the k-factor in dependence of the mass thickness t/lambda, and 2) Monte Carlo simulation approach, where an iterative procedure is used to calculate the k-ratios, based on bulk standards. The use of FIB lamellae allows excluding the fluorescence effect and incorrect Monte Carlo simulations due to incorrect assumptions of the microstructure below the surface, which is within the excitation volume.

Machining processes with main thermal impact like electro discharge machining (EDM) result in a change of temperature in the workpiece with temporal and spatial temperature gradients which have a large influence on the thermo-chemically modified surface microstructure and therefore a high impact on the functional properties of the workpiece. However, as most state variables (like the temperature) cannot be measured directly during processing, further insight can be gained only by simulations. This problem can be addressed by using micro structural features like the secondary dendrite arm spacing for calculating the cooling rate and by validating the simulated temperature profiles with these values. This study analyzes the subsurface microstructure of EDM machined 42CrMo4 steel with a ferrite-perlite and a quenched-tempered matrix by a range of microstructure analysis techniques. Results of electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA) and analysis of secondary dendrite arm spacing of secondary electron images are presented and their dependence on the main processing parameters is discussed qualitatively and quantitatively.

Carburizing is a thermo-chemical surface treatment through which a very hard martensitic layer develops in the external surface (case) of steel components resulting in substantial improvement in the fatigue life. Nevertheless, the overall fatigue properties of carburized steel components are yet severely dependent on the microstructure which develops in the interior region (core). This paper deals with the effects of core microstructure on bending fatigue behavior and fatigue crack growth of carburized steel parts. V-notched steel specimens were fabricated and subjected to two case hardening cycles where, respectively, bainitic-martensitic and ferritic-bainitic-martensitic microstructures developed in the core regions supported by similar fully martensitic microstructures in the case. 4-point plane bending fatigue tests were conducted to study the fatigue behavior of the heat-treated specimens. Furthermore, the effects of the core microstructures on fatigue crack growth resistance were also investigated. Hardness measurements revealed that both batches of specimens have similar hardness properties on the exterior surfaces, in the case-hardened layers and also in the cores. Moreover, the results showed that the specimens with the bainitic-martensitic core microstructure provide a marginally better fatigue performance in the finite life regime as compared to the ferrite-containing counterparts. More noticeable difference was, however, observed in the corresponding endurance limits where the former demonstrated a higher magnitude than the latter. Besides, the bainitic-martensitic core microstructure resisted the fatigue crack propagation more effectively than the ferrite-containing specimens.

Within the last decades significant improvements in the spatial resolution of electron probe microanalysis (EPMA) were obtained by instrumental enhancements. In contrast, the quantification procedures essentially remained unchanged. As the classical procedures assume either homogeneity or a multi-layered structure of the material, they limit the spatial resolution of EPMA. The possibilities of improving the spatial resolution through more sophisticated quantification procedures are therefore almost untouched. We investigate a new analytical model (M1-model) for the quantification procedure based on fast and accurate modelling of electron-X-ray-matter interactions in complex materials using a deterministic approach to solve the electron transport equations. We outline the derivation of the model from the Boltzmann equation for electron transport using the method of moments with a minimum entropy closure and present first numerical results for three different test cases (homogeneous, thin film and interface). Taking Monte Carlo as a reference, the results for the three test cases show that the M1-model is able to reproduce the electron dynamics in EPMA applications very well. Compared to classical analytical models like XPP and PAP, the M1-model is more accurate and far more flexible, which indicates the potential of deterministic models of electron transport to further increase the spatial resolution of EPMA.

In multi-phase steel grades such as ferrite-martensite dual phase (DP) steels, it is of the utmost importance to understand the underlying effects of solid phase transformations with respect to their consequences on the final mechanical properties. In the present research, by employing dilatometry experiments two equivalent DP microstructures have been designed which are identical in most primary aspects such as constituents’ volume fractions, the corresponding grain sizes and their morphologies. The difference, however, is the fashion in which carbon atoms in the martensite constituents are distributed. Electron probe microanalysis (EPMA) shows that excess carbon atoms which are rejected as a consequence of ferrite formation are accumulated in the adjacent austenite grains close to the boundaries yielding sharp carbon gradients. During final quenching, the characteristics of martensite transformation are therefore severely influenced. Through electron backscatter diffraction (EBSD) analysis many coarse substructures were detected in the interior regions of the inhomogeneous martensite associated with low dislocation densities. However, the areas close to the ferrite/martensite boundaries demonstrate finer substructures. Moreover, by means of nanoindentation tests it was found that the interior areas with lower carbon contents and coarser substructures show lower local strength as compared to the marginal regions. Macroscopic stress-strain behavior revealed that a higher ultimate tensile strength and enhanced post-uniform elongation are achieved in the specimen with sharp carbon gradients in its martensite constituents.

A review of the remaining challenges in electron probe microanalysis to quantify sub-micrometre features containing elements with a concentration less than 1 wt% is presented. These challenges derive from the equivocal influence of the main experimental parameters (accelerating voltage, beam current, measuring time and X-ray lines) on the achievable spatial resolution and the accuracy and precision of the quantification. This inter-dependence is demonstrated by examples from the literature and from new experimental results. From this survey, five key areas are identified as future research and development topics in order to solve for the discussed challenges and achieve the objective of quantification of low concentration elements using soft X-rays at high spatial resolution.

The prediction of X-ray intensities based on the distribution of electrons throughout solid materials is essential to solve the inverse problem of quantifying the composition of materials in electron probe microanalysis (EPMA) [3]. We present a hyperbolic conservation law for electron transport in solid materials and investigate its validity under conditions typical for EPMA experiments. The conservation law is based on the time-stationary Boltzmann equation for binary electron-atom scattering. We model the energy loss of the electrons with a continuous slowing-down approximation. A first order moment approximation with respect to the angular variable is discussed. We propose to use a minimum entropy closure to derive a system of hyperbolic conservation laws, known as the M1 model [11]. A finite volume scheme for the numerical solution of the resulting equations is presented. Important numerical aspects of the scheme are discussed, such as bounds for the finite propagation speeds, as well as difficulties arising fromspatial discontinuities in thematerial coefficients and the scaling of the characteristic velocities with the stopping power of the electrons.We compare the accuracy and performance of the numerical solution of the hyperbolic conservation law to Monte Carlo simulations. The results indicate a reasonable accuracy of the proposed method and showthat compared to the MonteCarlo simulation the finite volume scheme is computationally less expensive.

Interest in the use of EPMA at low voltage has grown considerably in recent years, mainly because of the availability of electron-beam instruments equipped with field-emission guns. However, EPMA at low voltage is marred by both experimental and analytical problems which may affect the accuracy of quantitative results. In the case of the analysis of transition elements, both the emission and absorption of X-rays are still poorly understood when they originate from electron transitions involving the partially filled 3d-shell. This is the case for the most intense Lα (L3-M5 transition) and Lβ (L2-M4 transition) lines. In this communication, we point out anomalies which appear to afflict the accuracy of EPMA of Ni-silicides using the Ni-Lα X-ray line and we discuss possible solutions.

Electron probe microanalysis and focussed ion beam milling are combined to improve the sensitivity and applicability of depth profiling quantification. With the nanoscale milling capabilities of the ion beam, very shallow bevels are milled by using a special preparation procedure to reduce any curtaining effect and minimize Ga ions implantation. A Ni/Cr multilayered specimen is used to evaluate the depth resolution. The best results are obtained by a well-focussed electron beam offered by a field-emission microprobe. A new evaluation algorithm is presented to quantify the structure in terms of mass thicknesses or if the density is known in terms of real thicknesses. The quantification procedure is based on Monte Carlo simulations where calculated k-ratios (calibrated X-ray intensities) are compared to the experimental ones to find the optimal structure. In comparison with an ion milled cross-section, the proposed bevel technique is more sensitive and provides more information about the material's structure.

Field emission (FE) electron gun sources provide new capabilities for high lateral resolution EPMA. The determination of analytical lateral resolution is not as straightforward as that for electron microscopy imaging. Results from two sets of experiments to determine the actual lateral resolution for accurate EPMA are presented for Kα X-ray lines of Si and Al and Lα of Fe at 5 and 7 keV in a silicate glass. These results are compared to theoretical predictions and Monte Carlo simulations of analytical lateral resolution. The experiments suggest little is gained in lateral resolution by dropping from 7 to 5 keV in EPMA of this silicate glass.

The high-temperature oxidation resistance of the carbide strengthened nickel-base alloy 602 CA is provided by the formation of a protective outer Cr2O3 scale accompanied by internal precipitation of alumina and dissolution of Cr-rich carbides. The carbide free zone formation has been discussed in the literature to be a consequence of either chromium depletion or alloy decarburization.A new dissolution mechanism is proposed in this paper. Carbide dissolution in alloy 602 CA exposed to oxidizing atmospheres at 1100 degrees C was studied. The alloy microstructure was characterized by means of SEM/EDX/EPIVIA and GDOES. The experimental observations were substantiated by CALPHAD based computations. (C) 2015 Elsevier Ltd. All rights reserved.

In optical diagnostic systems of ITER, mirrors will be used to guide the light from plasma towards detectors and cameras. The mirrors will be subjected to erosion due to fast particles and to deposition of impurities from the plasma which will affect adversely the mirror reflectivity and therefore must be suppressed or mitigated at the maximum possible extent. Predictive modeling envisages the successful suppression of deposition in the diagnostic ducts with fins trapping the impurities on their way towards mirrors located in the end of these ducts. To validate modeling predictions, cylindrical and cone-shaped diagnostic ducts were exposed in TEXTOR for 3960 s of plasma operation. After exposure, no drastic suppression of deposition was observed in the cylindrical ducts with fins. At the same time, no detectable deposition was found on the mirrors located at the end of cone-shaped ducts outlining the advantages of the cone geometry. Analyses of exposure provide evidence that the contamination of exposed mirrors was due to wall conditioning discharges and not due to working plasma exposure. Cleaning by plasma sputtering was performed on molybdenum mirrors pre-coated with a 100 nm thick aluminum film. Aluminum was used as a proxy of beryllium. During exposure in electron cyclotron resonance-generated helium plasma, the entire coating was sputtered within nine hours, leaving no trace of aluminum and leading to the full recovery of the specular reflectivity without detrimental effects on the mirror surface.

Journal Article Soft X-Ray EPMA Analyses of Extremely Reduced Phases from Apollo 16 Regolith: Problems and Solutions for Sub-Micron Analysis Get access P Gopon, P Gopon Dept. of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 USA Search for other works by this author on: Oxford Academic Google Scholar J Fournelle, J Fournelle Dept. of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 USA Search for other works by this author on: Oxford Academic Google Scholar P Sobol, P Sobol Dept. of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 USA Search for other works by this author on: Oxford Academic Google Scholar M Spicuzza, M Spicuzza Dept. of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 USA Search for other works by this author on: Oxford Academic Google Scholar P Pinard, P Pinard Gemeinschaftslabor für Electronenmikroskopie, RWTH 52074 Aachen, Germany Search for other works by this author on: Oxford Academic Google Scholar S Richter, S Richter Gemeinschaftslabor für Electronenmikroskopie, RWTH 52074 Aachen, Germany Search for other works by this author on: Oxford Academic Google Scholar X Llovet, X Llovet CCiTUB, University of Barcelona, ES-08028 Barcelona, Spain Search for other works by this author on: Oxford Academic Google Scholar JW Valley JW Valley Dept. of Geoscience, University of Wisconsin, Madison, Wisconsin 53706 USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 20, Issue S3, 1 August 2014, Pages 698–699, https://doi.org/10.1017/S1431927614005212 Published: 27 August 2014

The capabilities of field emitter electron microprobes to perform quantitative measurements at high spatial resolution are discussed. Using Fe-Cr-C particles in a bearing steel (SAE 52100) as example, a generic procedure was established to find the optimal analytical conditions (beam energy, beam current and acquisition time). The influence of these parameters on the accuracy, precision and spatial resolution was evaluated using experimental measurements and Monte Carlo simulations. A quantification procedure was developed for soft X-ray lines, taking into account the overlap of high order X-ray lines and background anomalies. The accuracy of Ka- and La-lines was verified using reference materials. A relationship between experimental and simulated X-ray intensities was determined to evaluate the measurement precision. The spatial resolution of each X-ray line was calculated from the simulated lateral and depth X-ray intensity distribution using simulations integrating experimentally measured beam diameters. The optimal analytical conditions for the studied sample were found to be 5 keV, 10 nA and 10 s acquisition time. Further specialized techniques to improve the spatial resolution are presented: focused ion beam preparation of thin lamella and wedge, and Monte Carlo based reconstruction. The feasibility of the latter to quantify features smaller than the X-ray emission volume was demonstrated.

The microstructure evolution in carbide strengthened Alloy 602 CA during exposure to a synthetic flue gas (N-2-2.5%O-2-8.6%H2O-16.4%CO2) at 1100 degrees C has been studied. The chromium and aluminium loss resulted in a chromium depleted alloy subsurface area and the dissolution of the carbides within this area. An increase of the carbide fraction in the sample core was observed and quantified. Phase equilibria calculations revealed that the depletion of aluminium as well as that of chromium triggers carbon to leave the depleted area. The overall carbon depletion in that area corresponded to the observed increase in carbide fraction in the sample core. (c) 2013 Elsevier Ltd. All rights reserved.

This study aims to characterise the microstructure and model the flow curve behaviour of bainite-aided DP steel. First, combined electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) measurements were applied to quantify the constituents (ferrite, martensite, and bainite) in the microstructure. Then, the flow behaviour of the material was modelled using the microscale finite element method by considering the effect of the microstructures using the representative volume element (RVE) approach based on real microstructure. The flow behaviour of single phases (ferrite, martensite, and bainite) was modelled using the dislocation-density-based work-hardening approach, whereas the model parameters were identified using microstructural features. The flow curves predicted from the 2D RVE calculations were correlated to 3D using a correlation factor. Good agreement between the 3D correlated and experimental flow curves was only achieved when bainite was considered in the RVE modelling. The presence of bainite reduces the internal stress gradients while increasing the overall strength of the material.

In ITER, mirrors will be used as plasma-viewing elements in all optical and laser diagnostics. In the harsh environment mirror performance will degrade hampering the operation of associated diagnostics. The most adverse effect on mirror performance is caused by the deposition of impurities. It is expected that the most challenging situation will occur in the divertor. With the envisaged changes to all-metal plasma-facing components (PFCs) in ITER, an assessment of mirror performance in an existing divertor tokamak with allmetal PFCs is urgently needed. Molybdenum and copper mirrors were exposed for nearly nine months in ASDEX Upgrade which has alltungsten PFCs. Mirrors were located at the inner wall, under the dome and in the pump-duct. During exposure, the mirrors were heated to temperature in the range 145C-165C. This was made to approach the expected level of heating due to absorption of neutrons and gammas on mirrors in ITER divertor. After exposure, degradation of the reflectivity was detected on all mirrors. The highest reflectivity drop was measured on mirrors under the dome facing the outer strike point, reaching -55% at 500 nm. The least degradation was detected on mirrors in the pump duct, where the reflectivity was preserved in the range 500-2500 nm and the largest decrease was about -8% at 250 nm. On all contaminated mirrors carbon fraction did not exceed 50 at.% while the major contaminants were metals and oxygen. The degradation of exposed mirrors underlines the necessity for urgent R&D on deposition mitigation and in-situ mirror cleaning in ITER.

In ITER, mirrors will be used as plasma-viewing elements in all optical and laser diagnostics. In the harsh environment, mirror performance will degrade hampering the operation of associated diagnostics. The most adverse effect on mirror performance is caused by the deposition of impurities. It is expected that the most challenging situation will occur in the divertor. With the envisaged changes to all-metal plasma-facing components (PFCs) in ITER, an assessment of mirror performance in an existing divertor tokamak with all-metal PFCs is urgently needed.Molybdenum and copper mirrors were exposed for nearly nine months in ASDEX Upgrade which has all-tungsten PFCs. Mirrors were located at the inner wall, under the dome and in the pump duct. During exposure, the mirrors were heated to temperature in the range 145-165 degrees C. This was made to approach the expected level of heating due to absorption of neutrons and gammas on mirrors in the ITER divertor. After exposure, degradation of the reflectivity was detected on all mirrors. The highest reflectivity drop was measured on mirrors under the dome facing the outer strike point, reaching -55% at 500 nm. The least degradation was detected on mirrors in the pump duct, where the reflectivity was preserved in the range 500-2500 nm and the largest decrease was about -8% at 250 nm. On all contaminated mirrors carbon fraction did not exceed 50 at% while the major contaminants were metals and oxygen. The degradation of exposed mirrors underlines the necessity for urgent R&D on deposition mitigation and in situ mirror cleaning in ITER.