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

tel-00751814, version 1 - 14 Nov 2012
I.3. Mechanically alloyed NDS steel (MA NDS)
Chapter 2. Materials, experimental and simulation techniques
NDS steels were elaborated following two distinct ways. The first one is mechanical
alloying. In this case, pre-alloyed powder Fe-18Cr-1W-0.14N is mechanically alloyed with
0.5 wt.% of titanium hydrate (TiH2) in laboratory attritor ball mill. Mechanical alloying is
performed in CEA (SRMA/LTMEX), Saclay. Initial sizes of pre-alloyed powder and TiH2 are
100 µm and 100 nm respectively. Parameters of milling are the following:
o Atmosphere: gas argon.
o Milling time: 10 hours.
o Milling speed: 400 rpm.
o The ratio of the mass of the balls to the powder mballs/mpowder: 15.
o Balls: stainless steel 440
Nominal composition of MA NDS steel is detailed in Table 2.3.
Table 2.3. Nominal composition of Fe-18Cr-1W-0.14N NDS steel (J12). Balance is iron.
Cr W N Ti
wt.% 18 1 0.14 0.5 (TiH2)
at.% 19 0.30 0.54 0.57
In order to study the precipitation process (nucleation, growth as well as coarsening
stages) as-milled powder is subjected to different annealing treatments at 600, 700, 850,
1000°C, during 1hour. Annealing is performed under hydrogen atmosphere. After annealing
powders are air cooled.
In order to get bulk material, as-milled powder is degassed at 300°C during 10 hours,
then pre-heated at 800°C/1h and finally hot extruded (SRMA code J12).
The APT characterisations were performed after on the following states:
o as-milled state;
o annealed at 600°C during 1h;
o annealed at 700°C during 1h;
o annealed at 850°C during 1h;
o annealed at 1000°C during 1h;
o consolidated state.
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