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

tel-00751814, version 1 - 14 Nov 2012
Concentration of Cr, N and Fe
(at,%)
100
90
80
70
60
50
40
30
20
10
Chapter 4. Nitride Dispersion Strengthened Steels
Figure 4.36. Composition profile through particles observed in nitrided NDS steel
annealed at 700°C during 1h. Profile is drawn perpendicularly to particles denoted as (1) as
indicated by black dashed line on Figure 4.35-(1). Sampling volume is 3×3×1 nm 3 ; λ is the
characteristic distance between two Cr-N rich particles. Only Cr, N and Fe concentrations
(at.%) are shown.
The compositions of particles denoted as (2) are shown on Figure 4.37. It can be seen,
some Ti as well as traces of Al is detected. The measured Cr concentration in these particles
varies from 45.7 to 55.5 at.% and it is quite constant. However, the variation of N
concentration from 25 to 47 at.% is noted. Some of these particles appear more enriched in
N. Thus, the mean chemical compositions are calculated separately for both types of
nanoparticles (more and less enriched in N). The mean chemical composition for
nanoparticles less enriched in N (denoted as (2)) is following: 52.4±3.3 Cr, 28.1±3.0 N,
18.4±1.0 Fe and 0.73±0.6 Ti at.%. The chromium over nitrogen ratio (Cr/N) is 1.9±0.2.
Their stoichiometry is approximately corresponding to Cr2N like in case of nanoparticles
denoted as (1). The mean chemical composition for thicker particles more enriched in N
(denoted as (2),) is the following: 50.9±2.2 Cr, 42.9±2.2 N, 5.0±1.0 Fe, 0.6±0.3 Ti and
0.41±0.3 Al at.%. The chromium over nitrogen ratio (Cr/N) is 1.2±0.1and their stoichiometry
is approximately corresponds to CrN. Thus, the APT data is consistent with existence of
Cr2N and CrN nanoparticles.
0
λ
0 5 10 15 20 25 30 35 40
Thickness
Distance (nm)
Cr
N
Fe
173