Erkki Heikinheimo

Monte Carlo Simulation of Secondary Fluorescence in Small Particles and at Phase Boundaries

Abstract. Results from Monte Carlo simulations and experimental measurements of X-ray spectra of small Cu-particles in Fe-containing slags are presented. The analyzed Cu-particles remain suspended in flash smelting and Cu converter slags, which contain Fe up to about 33 wt%, and have diameters ranging from 5 up to 100 μm. Conventional standardless analysis of measured X-ray spectra gives an apparent Fe content of ∼ 1–5 wt%, depending on the particle diameter, which cannot be explained in terms of the thermodynamic solubility of Fe in solid Cu. In order to study the influence of the Fe-containing slag to the apparent Fe content in the particles, X-ray spectra have been computed by means of Monte Carlo simulation of the coupled electron and photon transport. The simulation code used is largely based on the general-purpose simulation package PENELOPE and it incorporates ionization cross sections evaluated from an optical-data model and bremsstrahlung cross sections that reproduce radiative stopping power derived from partial wave calculations. Simulated Fe k-ratios, for different experimental situations, have been found to be in satisfactory agreement with measurements. The apparent Fe content is explained in terms of secondary fluorescence of Fe Kα by Cu Kα X-rays.

Chemical interaction between Fe and silicon nitride ceramic

Abstract Chemical reaction between silicon nitride ceramic and iron metal was studied experimentally with diffusion couples at 1100–1150 °C in order to clarify mechanisms in direct bonding of Si 3 N 4 to Fe-based alloys. The reaction products have been characterized and related to the thermodynamic data available. The extent of reaction is controlled by the nitrogen gas pressure build-up at the metal-ceramic interface and the rate by silicon diffusion into the metal. Under the experimental conditions, only an Fe(Si) solid solution was formed with maximum silicon content of about 12 at%. No silicides were found at the metal-ceramic interface. Nitrogen gas evolved at the interface is removed by permeation through the metal and/or through pores. Annealing atmosphere and sintering aid materials in the ceramic may play a role in the interaction.

Electron Probe Microanalysis of Ni Silicides Using Ni-L X-Ray Lines

We report electron probe microanalysis measurements on nickel silicides, Ni5Si2, Ni2Si, Ni3Si2, and NiSi, which were done in order to investigate anomalies that affect the analysis of such materials by using the Ni L3-M4,5 line (Lα). Possible sources of systematic discrepancies between experimental data and theoretical predictions of Ni L3-M4,5 k-ratios are examined, and special attention is paid to dependence of the Ni L3-M4,5 k-ratios on mass-attenuation coefficients and partial fluorescence yields. Self-absorption X-ray spectra and empirical mass-attenuation coefficients were obtained for the considered materials from X-ray emission spectra and relative X-ray intensity measurements, respectively. It is shown that calculated k-ratios with empirical mass attenuation coefficients and modified partial fluorescence yields give better agreement with experimental data, except at very low accelerating voltages. Alternatively, satisfactory agreement is also achieved by using the Ni L3-M1 line (Lℓ) instead of the Ni L3-M4,5 line.

Forming and fracture limits of aluminium alloy

Abstract Forming and fracture limits of an AA 3104-H19 aluminium alloy sheet were studied by hydraulic bulging and Marciniak type deep drawing and tensile tests. The alloy appeared to be highly anisotropic, exhibiting distinctly different fracture patterns in the rolling and transverse directions. The preferred fracture direction was transverse to the rolling direction. In the tensile test, samples loaded in the rolling direction failed transverse to the rolling direction, but in the transverse direction, the fracture was inclined at ∼55° to the tensile axis. In some cases, two such competing fractures in the characteristic directions could be observed. Scanning electron microscopy studies revealed a typical ductile fracture pattern. The fracture occurred by shearing in the through thickness direction, and typical alternating shear lips in a direction inclined at ∼45° to the through thickness direction could be observed. Forming limit diagrams for both rolling and transverse directions were determined from the experiments. The measured limit strains in uniaxial tension were predicted well by the modified Rice–Tracey theory, but in equibiaxial tension, the theory overestimated the fracture limit strains.

Towards Reliable Quantification of Steel Alloys at Low Voltage

Whether it be inclusions, precipitates or segregation at grain boundaries, the development of new steel alloys and processes hinges on the chemical quantification of submicrometer features. The combined requirements for high spatial resolution and accurate measurements of several elements make field emission electron microprobes suitable instruments for studying steel alloys. For quantitative analyses, the spatial resolution is determined by the x-ray emission volume the dimensions of which depend on the sample composition, the beam energy and the overvoltage ratio. For most elements, lowering the beam energy directly translates into the necessity of using lower energy x-ray lines. However, the improvement of the spatial resolution comes with additional challenges, mainly a lower intensity (worst statistics), a larger influence of contamination and oxidation, and inaccuracies of the quantification.

Electron probe microanalysis of Ni-silicides at low voltage: difficulties and possibilities

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.

Role of native metal oxide layer on emitted metal L line in low-voltage electron-probe microanalysis

Abstract The thickness of the native oxide layer formed on bulk samples of metals Cu, Fe, Ni and Ti exposed to the ambient atmosphere for different exposure times, ranging from minutes up to 2500 hours, has been determined by electron-probe microanalysis (EPMA). Thicknesses were obtained by measuring the intensity of the OKα line emitted from the studied samples at varying electron incident energies, and analysing it with the help of an EPMA thin-film program. Using the thickness values obtained, the intensity loss of the metal L-line, due to the presence of the native oxide layer, has been calculated. This ranges from 5–8% at 2 keV to 1–2% at 10 keV for Cu, Fe and Ni, while for Ti it goes from 10 to 30% at 2 keV to 1–2% at 10 keV, depending on the exposure time. A correction to compensate for the metal L-line intensity loss due to the native oxide layer is discussed.

Melting Behavior of Sn–Bi Alloy Powder Compacts Observed Using Optical Dilatometry

Abstract The melting behavior of Sn – Bi alloy powder compacts was observed using optical dilatometry. The change in standard deviation of compact width with temperature obtained by dilatometry was used to evaluate the melting behavior by considering the factors in the shape change of the compact under heating. The effects on melting behavior of alloy composition, particle size and pressing load at compacting are discussed in this study. The difference in composition affected the melting behavior in accordance with the phase diagram. Smaller particle size showed a lower degree of melting. The effects of these two parameters, viz. composition and particle size, however, are highly dependent on surface oxidation of powders. The influence of surface oxidation, on the other hand, was reduced by producing the compacts with a higher pressing load.