Seminar from Andrius MARTINAVICIUS


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Date | Time
15/10/2014 | 11 h 00 min - 13 h 00 min

Location
Salle du Conseil – IJL – Saurupt

Categories


Andrius Martinavicius

Normandie University, Groupe de Physique des Matériaux, UMR 6634 CNRS, Université de Rouen, INSA Rouen, 76801 Saint Etienne du Rouvray, France
Université de Lorraine, Institut Jean Lamour, UMR 7198 CNRS, Parc de Saurupt CS 14234, F-54042 Nancy, France
viendra nous présenter ces travaux réalisés lors de son post-doc au sein du Labex DAMAS :

Atom probe analysis of nitrided layers in steels: advantages and difficulties

Atom probe tomography (APT) is a technique providing three-dimensional mapping of elements within a small volume of material with a near-atomic resolution [1]. It has shown its potential in studying nitrided steels providing a tomographic view of precipitated nitrides [2],[3]. Despite the remarkable ability to provide three dimensional images of analyzed specimen the quantitative measurement of nitrogen concentration is rather complicated. Since in APT the identification of ions is based on time of flight, ions with the same mass-over-charge ratio will overlap. If the alloy contains some Si, peaks from 28Si++ and 14N+ will overlap in mass spectra preventing correct identification. In addition, part of N potentially evaporates as N2+ and N2++ overlapping with 56Fe++ and N+, respectively. The problem is addressed by nitriding pure Fe with nitrogen enriched to 50% in 15N has been used. It has been possible to establish the relative abundances of different nitrogen molecular species, and quantify the different peak overlaps. Despite the various correction applied to account for these overlaps, the measured nitrogen concentration was still lower than expected. This difference was smaller for lower atom probe analysis temperatures. The possible loss mechanisms will be discussed. The problem of overlap between the peaks of 28Si++ and 14N+ can be party overcome by employment of pure 15N. The advantage of 15N is demonstrated in Fe-Si alloy, where cubic amorphous Si3N4 precipitates form during nitriding.

[1] Kelly TF, Miller MK. Invited review article: Atom probe tomography. Rev Sci Instrum 2007;78(3):031101.

[2] Jessner P, Danoix R, Hannoyer B, Danoix F. Investigations of the nitrided subsurface layers of an Fe-Cr-model alloy. Ultramicroscopy 2009;109(5):530–4.

[3] Jessner P, Gouné M, Danoix R, Hannoyer B, Danoix F. Atom probe tomography evidence of nitrogen excess in the matrix of nitrided Fe-Cr. Phil Mag Lett 2010;90(11):793–800.