Page 242 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 4 CONTROL OF NANOSTRUCTURE OF MATERIALS

1200 300
Tensile strength / MPa 800 200 Vickers hardness / HV ψιελδ στρεσσ σ 02 /GPa Azushima’s

400
100
data

0 1 2 3 4 5 6 7 8
Pass number
Commercial pure iron
Figure 4.4.21
Relationship between tensile strength or Vickers hardness
Grain size d -0.5 /m -0.5
and pass number.
Figure 4.4.23
Relationship between yield stress and grain size of ultra
low-carbon steel.
30
60
these specimens show good agreement with the stan-
Elongation / % 20 40 Reduction / % Takagi [8].
dard Hall–Petch relationship of iron obtained by
(3) Advanced ECAP processes

10 Figure 4.4.24 shows the fundamental process of metal
flow during ECAP. As shown in the figure, the chan-
20
nel is bent through an angle equal to 90 . The speci-
men is inserted within the channel and it can be
pressed through the die using a punch. There are four
basic processing routes in ECAP. In route A, the spec-
0 1 2 3 4 5 6 7 8
imen is pressed without rotation, in route B the spec-
Pass number A
imen is rotated by 90 in alternate direction between
consecutive passes, in route B the specimen is
C
Figure 4.4.22 rotated by 90 in the counterclockwise between each
Relationship between elongation or reduction and pass pass, and in route C the specimen is rotated by 180
number of Irmco steel.
between passes.
Figure 4.4.25 shows the macroscopic distortion
increased by a factor of 2.5 after one pass in compari- introduced into a cubic element for up to a maximum
son with the specimen before ECAP process and it of 98 passes through the die [9]. From these
increases with increasing pass number up to 8 passes. distortions, the influence of the processing route on
The tensile strength is over 800 MPa after 8 passes. On the development of an ultra-fine grained microstruc-
the other hand, the elongation shows a reduction from ture can be considered. Iwahashi et al. [10] reported
20% for the specimen before ECAP process to several that the ultra-fine grained microstructure of pure alu-
percent after 8 passes as shown in Fig. 4.4.22 [7]. minum after 10 passes in route A was the same that
Horita et al. and Azushima et al. reported the same of after 4 passes in route B .
C
results for the aluminum alloys and for the steels,
respectively. In particular, Azushima et al. [5] reported (4) Material development by ECAP
that the tensile strength after 10 passes of repetitive Although ECAP is generally used in the processing of
side extrusion was over 1,000 MPa. It has increased solid metals, it may be used also for the consolidation
by a factor of 3 in comparison with the as-received of metallic powder. Kudo et al. [11] carried out the
material. The experimental data of the specimen after pressing of pure aluminum powder by the repetitive
10 passes are plotted in the Hall–Petch relationship side extrusion applied to the back pressure at a room
of the yield stress against the root grain size as temperature and they reported that the relative density
shown in Fig. 4.4.23. In this figure, the results for after pressing became over 99.6%.

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