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allied
academies
Materials-Metals 2017
Page 49
November 16-17, 2017 Paris, France
13
th
Annual Conference on
Materials Science, Metal and Manufacturing
Journal of Materials Science and Nanotechnology
Volume 1 Issue 2
Microstructure evolution and nitriding behaviors
of Sm-Fe alloys in rapid solidification process
Chunyan Song, Shuhuan Wang, Kaixuan Zhang, Dingguo Zhao
and
Yongliang Gui
North China University of Science and Technology, China
R
apid solidification technology is used widely to fabricate
micro-crystalline and amorphous alloys. Compared
to the alloys produced under equilibrium solidification
conditions, smaller grain size and more grain boundaries in
rapidly solidified alloys are undoubtedly beneficial for the
diffusion of atoms in heat treatment process. In traditional
nitriding process of coarse-grained Sm-Fe alloys, it is hard
to further increase the nitrogen content and improve the
uniform of nitrogen distribution. Therefore, the nitriding
behaviors and microstructure evolution of rapidly-solidified
Sm-Fe alloy ribbons with micro-crystalline and amorphous
structure were investigated in this work. Several Sm-Fe alloy
ribbons with a nominal chemical composition of 30% (wt.,
%) were manufactured by melt spinning technology at Ar
atmosphere. Microstructure of these rapidly solidified Sm-
Fe alloys manufactured under different rotating velocities
was characterized with OM, SEM and XRD. The nitrogen
content penetrated in rapidly solidified Sm-Fe alloys
was examined and the morphologies of nitrogen were
investigated. Results indicate that with the rotating velocity
of wheel increases from 6 m/s to 36.5 m/s, the thickness of
Sm-Fe alloy ribbon decreases by one order of magnitude, i.e.
from 107.70 µm to 18.93µm, and the cooling rate increases by
approximately six times, i.e. from 1.86×105 K/s to 1.08×106
K/s, microstructural characteristics transform from coarse
dendrites to cellular crystal, microcrystal, mixture of crystal
and amorphous phase. Moreover, Sm and Fe elements in alloy
ribbons tends to uniform compare with the as-cast alloys
according to the laser ablation inductively coupled plasma
mass spectrometry map. The size of all grains is still less than
10μm although the crystalline grains grew during nitriding
process of rapidly solidified Sm-Fe alloy at 420
0
C. This result
suggests that smaller grain size and more grain boundaries of
rapidly solidified Sm-Fe alloy could provide more locations
for atomic nitrogen absorption in the nitriding process, and
then improve the diffusion of nitrogen atoms. However,
most nitrogen penetrated in rapidly solidified Sm-Fe alloys
are distributed on the boundaries of cellular grains in the
forms of nitrogenous compounds. A quickly quenched
Sm-Fe alloy ribbon with a stable near-stoichiometric
Sm
2
Fe
17
phase and amorphous matrix in microstructure
was fabricated successfully when the rotating velocity of
wheel was greater than 34 m/s. After nitridation of quickly
quenched Sm-Fe alloy ribbons, the constitutional phases are
crystalline Sm
2
Fe
17
Nx and α-Fe, and amorphous nitrides. This
phenomenon indicates that nitrogen atoms are distributed
not only in crystalline phase but also in amorphous matrix.
The nitrogen content in Sm-Fe alloy ribbons is up to 4.155%,
which indicated the microstructure characteristics of quickly
quenched Sm-Fe alloy is helpful for the improvement of
nitrogen absorption.
scy7825@163.comMater Sci Nanotechnol 2017, 1:2