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

tel-00751814, version 1 - 14 Nov 2012
Chapter 3. Oxide Dispersion Strengthened Steels
Fe-9/18Cr-Ti (Ø = 100 µm)
0,5 wt.% Y 2O 3 (Ø = 20 nm)
1. Before mechanical alloying
Fe
Y-O
Size ~ 2-3 nm
100 µm
Fe cristallite (15 nm)
Fe cristallite (100 nm)
Fe
(YTiO 2)
Size 3 nm
2. After mechanical alloying 3. After mechanical alloying
+
heat treatment
MA provides two simultaneous
mechanisms: i) dissolution of Y2O3
initial oxide with supersaturation of Y
and O in the matrix (64, and 72 at.%
respectively for Y, O) and ii) formation
of Y-O-enriched aggregates by a)
direct transformation Y2O3 to Y-O rich
particles or b) dissolution and
subsequent nucleation.
After subsequent annealing
(850°C/1h) or hot extrusion
Y-O nanoparticles act as a
nuclei for formation of Ti-
Y-O nanoparticles. Y, O
and mostly Ti are
incorporated into these
nuclei resulting in their
enrichment.
Figure 3.17. Mechanism of nanoparticles formation in ODS steel after [6].
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