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

tel-00751814, version 1 - 14 Nov 2012
Chapter 1.Bibliography
II.2. Ferritic/Martensitic (F/M) steels
These materials offer more advantages and are potential candidates for SFR claddings as
well as for other Gen IV designs [14,15]. Commercial ferritic/martensitic steels based on 9-
12%Cr exhibit the highest swelling resistance in comparison with austenitic steels (Figure
1.5). This low swelling response appears to be a generic property of ferritic alloys [20,21]. In
addition these materials have high thermal conductivity and low thermal expansion. A
limitation to the use of ferritic–martensitic steels is their creep resistance at temperatures
(400-600°C) desired in the Gen IV systems. One approach to extend the range of operation
temperatures of F/M steels is reinforcing the F/M lattice by stable dispersion of nanoparticles.
II.3. Nano-reinforced steels
One example of such nano-reinforced steels may be Oxide Dispersion Strengthened steels
(ODS). These materials are presently achieve increasing attention and currently considered as
cladding materials for SFR and several types of Gen IV systems [22,23].
These materials show remarkable properties due to high density (~10 23 to ~10 24 m -3 ) of
nanometre scale oxide particles (1-10 nm in diameter) dispersed in Fe-Cr matrix. These nano-
oxides are found to be extremely resistant to coarsening (even during ageing at 900°C for
times up to 3000 h [24,25]). They act as i) obstacles to dislocation motion [26], providing
high creep strength in the range of interest [27–30] for SFR application and ii) sinks for
radiation induced point defects, providing good radiation resistance [31–34].
Properties of such ODS steels strongly depend on microstructure that requires close
control over nanoparticles density, size, interfacial properties, etc.
Elaboration way, influence of chemical composition and elaboration parameters on final
microstructure, as well as study of nano-oxides will be discussed in next section.
III. Elaboration process of ODS
ODS steels are usually produced by complex powder metallurgy technique: mechanical
alloying (MA). This process is a dry, high energy ball-milling process, where elemental or
pre-alloyed powders (Fe, Cr etc…) are milled together with oxide dispersoid and
subsequently mechanically homogenized [31–35]. After MA the powder is consolidated by
powder metallurgical processes, as Hot Isostatic Pressing (HIP) or Hot Extrusion (HE). Then
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