Effect of Mn and Cr on the selective oxidation, surface segregation and hot-dip Zn coatability

The effect of the dew point (and therefore oxygen partial pressure) on the selective oxidation of Advanced High Strength Steels was investigated. Steels with different Si contents, 0.2 wt% Si, 0.8 wt% Si and 1.5 wt% Si were used. The steel samples were annealed at 840 °C for 60 s and various gas atmospheres prior to hot-dip galvanized at 460 °C. The dew point of the 5 % H2-N2 annealing atmosphere was lowered from-30 °C (equivalent to 380 ppm H2O) to-58 °C (equivalent to 14 ppm H2O) in order to investigate surface segregation of alloying elements Si, Mn and Cr. These conditions are reducing for Fe, but oxidizing the oxygen-affine elements. Oxide morphology changed from a complete covering surface at high dew point to separated oxide spots at grain boundaries at low dew point. At the low dew point Cr was not oxidized. Oxides with a low Mn/Si-ratio seems to be amorphous. The Si-oxides are especially located at grain boundaries, Mn-oxides tend to cover the surface. Oxides covering the steel surfaces are detrimental for subsequent procedures as hot dip galvanizing, painting and welding.

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Near-Surface Aggregation of Sn In Heavily Sn-Doped GaAs Films Grown By Molecular Beam Epitaxy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100118710 ◽

1985 ◽

Vol 43 ◽

pp. 368-369

Author(s):

S. H. Chen

Keyword(s):

Molecular Beam Epitaxy ◽

Cross Section ◽

Electron Spectroscopy ◽

Molecular Beam ◽

Surface Segregation ◽

Secondary Ion Mass Spectrometry ◽

Specimen Preparation ◽

Near Surface ◽

Gaas Films ◽

Secondary Ion

Sn has been used extensively as an n-type dopant in GaAs grown by molecular-beam epitaxy (MBE). The surface accumulation of Sn during the growth of Sn-doped GaAs has been observed by several investigators. It is still not clear whether the accumulation of Sn is a kinetically hindered process, as proposed first by Wood and Joyce, or surface segregation due to thermodynamic factors. The proposed donor-incorporation mechanisms were based on experimental results from such techniques as secondary ion mass spectrometry, Auger electron spectroscopy, and C-V measurements. In the present study, electron microscopy was used in combination with cross-section specimen preparation. The information on the morphology and microstructure of the surface accumulation can be obtained in a fine scale and may confirm several suggestions from indirect experimental evidence in the previous studies.

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A New Numerical Model for Electron-Probe Analysis at High Depth Resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010016491x ◽

1996 ◽

Vol 54 ◽

pp. 490-491

Author(s):

P.-F. Staub ◽

C. Bonnelle ◽

F. Vergand ◽

P. Jonnard

Keyword(s):

Electron Probe ◽

Surface Segregation ◽

Depth Distribution ◽

Computing Time ◽

Depth Resolution ◽

Physical Parameters ◽

Electron Probe Analysis ◽

Interface Phases ◽

Excitation Conditions ◽

High Depth

Characterizing dimensionally and chemically nanometric structures such as surface segregation or interface phases can be performed efficiently using electron probe (EP) techniques at very low excitation conditions, i.e. using small incident energies (0.5<E0<5 keV) and low incident overvoltages (1<U0<1.7). In such extreme conditions, classical analytical EP models are generally pushed to their validity limits in terms of accuracy and physical consistency, and Monte-Carlo simulations are not convenient solutions as routine tools, because of their cost in computing time. In this context, we have developed an intermediate procedure, called IntriX, in which the ionization depth distributions Φ(ρz) are numerically reconstructed by integration of basic macroscopic physical parameters describing the electron beam/matter interaction, all of them being available under pre-established analytical forms. IntriX’s procedure consists in dividing the ionization depth distribution into three separate contributions:

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