Chemistry Reference
In-Depth Information
1,00
0,99
-8
-6
-4
-2
V (mm/s)
Fig. 4.31 Zoom of peaks 1 and 2 of the Mössbauer spectrum of the Fe
67.5
Ni
32.5
sample milled
for 10 h. The inset represents the whole spectrum. One distinguishes the BCC, FCC magnetic
components and the quadrupolar single line component [
178
]
Fig. 4.32 300 K Mean
hyperfine field values as a
function of Ni content [
178
]
36
32
28
-Fe
Melt
MA 10h
α
24
0
20
40
60
80
100
Ni (at.%)
powders (22.5 \ x \ 40 at.%) mechanically alloyed (MA) for 10 h [
178
]. It is
evidenced from X-ray diffraction that the nanostructured alloys consist of both body-
centred cubic and face-centred cubic crystalline phases. Consequently, the hyperfine
structures had to be described by a fitting model involving two hyperfine magnetic
field distributions and a narrow singlet (see Figs.
4.30
and
4.31
). One distribution
was attributed to the ferromagnetic BCC grains of tetrataenite) while the second one
was assigned to the ferromagnetic grains of taenite, and the narrow singlet to para-
magnetic grains of antitaenite (i.e. superparamagnetic grains). This careful
description allows to follow the hyperfine field at Fe as a function of the Ni content,
giving rise to a jump at about 32.5 at.% Ni as illustrated in Fig.
4.32
, attributed to
Invar anomaly [
178
].
