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

tel-00751814, version 1 - 14 Nov 2012
Concentration Concentration (at,%) (at,%)
100
90
80
70
60
50
40
30
20
10
0
λ
λ λFe+Cr Fe
Chapter 3. Oxide Dispersion Strengthened Steels
λY-Ti-O λ YTiO
Fe-Cr phase Y-Ti-O phase
0 5 10 15 20 25 30 35 40 45 50 55 60
Distance (at,%)
Figure 3.2. Profile generated from a volume in Figure 3.1 (b). Characteristic lengths
of Y-Ti-O – λY-Ti-O and Fe-Cr-rich phases and Fe-rich phases – λFe+Сr are shown. Fe, Cr, Mn,
Si, C, W species are associated with Fe-Cr-rich phase while Y, YO, O/O2, Ti, TiOx, FeO,
CrOx with Y-Ti-O phase. Profile is 12×12×60 nm 3 with step of 0.2 nm.
A similar two-phase microstructure was also observed in a different analysis (LATAP
analyse, see Figure 3.6) while a one phase structure, corresponding to Fe-Cr-rich phase has
been observed in the last experiment, Figure 3.3. This non homogeneous microstructure can
be explained simply looking at the microstructure observed during APT tip preparation in
SEM / FIB (Figure 3.4). Different contrasts (bright and dark) clearly reveal that a two phase
structure is present. The shape of both phases is not well defined and irregular. From SEM
picture it is clear that, the dimensions of these phases vary between tens of nanometres to
several micrometers. So, the dimensions of these phases, can explain the different
microstructures observed by 3DAP.
Fe
Cr
W
10×10×70 nm 3
Figure 3.3. 3D reconstruction of ODS model alloy analysed by LATAP. Fe, Cr, W are
shown. No presence of Y-Ti-O-rich phase is observed. Analyzed volume is 10×10×70 nm 3 .
93