Etude par Sonde Atomique Tomographique de la formation de nano ...

tel-00751814, version 1 - 14 Nov 2012
Chapter 4. Nitride Dispersion Strengthened Steels
Cr segregation is detected for all studied GBs within this temperature condition. The
relative excess of Cr (Cboundary/Cmatrix) varies from 1.44 to 1.6. As for Ti, N(Si) and W,
enrichments are clearly visible at several GB but not in all cases.
b) Powder annealed at 700°C/1h
3D atom maps showing GBs and nanoparticles in powder annealed at 700°C during 1h
are shown Figure 4.2 (a). The enrichment of Cr, N(Si), Ti, in less extend W and Mn is
visible. Composition profiles shown on Figure 4.2 (b), clearly revealed Cr, Ti, N(Si), W and
Mn enrichment on GB as well. As for Cr, like in the previous case (600°C), the relative
excess varies from one GB to another. Variations from 1.4 to 2.1 are observed.
(a)
(b)
Figure 4.2. Grain boundaries observed in MA NDS powder annealed at 700°C during
1h. (a) 3D atom maps are shown for Cr, Ti, W, Mn and N(Si) species; Ti-enrichment
corresponding to nanoparticles can be seen in Ti map (dashed circles) (b) Variation of
Cboundary/Cmatrix measured across the grain boundary as indicated by the arrow in (a). (Cr and
Fe are on the left profile and N(Si), Ti, Mn and W species on the right one). Cboundary
corresponds to the concentration measured in a sampling volume of 6×8×1 nm 3 . Cmatrix is
equal to the concentration of the element measured in the matrix.
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