Page 241 - Book Hosokawa Nanoparticle Technology Handbook

4.4 NANOCOMPOSITE STRUCTURE FUNDAMENTALS
that the strong filamentary microstructure is devel-
oped with increasing number of pass. In these condi-
tions, the observation of microstructure must be made
using the TEM analyzer. From the TEM microstruc-
ture analysis, it has been confirmed that the many
metals with an ultra-fine grain size under 1
m are
developed by ECAP processes. Valiev et al. [2]
reported that the ultra-fine grain with a sub-micron
was created by ECAP processes in the many metals
and the grain size of the AL-4%Cu-0.5%Zr alloy
became about 200 nm by ECAP with a plastic strain
of 7 at 160°C. Horita et al. [3] reported that the alu-
minum and aluminum alloys with a submicron-scaled
grain size were developed by ECAP processes.
Azushima et al. [6] reported that the ultra-fine grain
size with a major axis length of 0.5
m and a minor
axis length of 0.2
m was developed by 10 passes of
repetitive side extrusion as shown in Fig. 4.4.20.
(b) Mechanical properties
From the TEM observation of microstructure, it is
expected that the hardness and the tensile strength of
metals with the ultra-fine grain become higher by the
repetitive side extrusion. Figure 4.4.21 shows the rela-
tionship between the hardness, tensile strength, and
pass number of ECAP for Armco steel [7]. The hard-
ness and the tensile strength increase with increasing
pass number. The Vickers hardness is increased from
Figure 4.4.19 100 to 250 and the tensile strength is increased from
Schematic representation of side extrusion process of 300 to 750 MPa after one pass. The tensile strength is
ECAP type.

order to produce the uniform shear deformation and
present the defect of workpiece.
The schematic representation of this process is
shown in Fig. 4.4.19. The specimen is side extruded
through the shear deformation zone with and due to
the dead zone in the outer corner of the channel.
When the workpiece is side extruded through the
channel, the total strain is
1 ⎧ ⎛ ⎞ ⎛ ⎞ ⎫
⎨ 2cot ⎜ ⎟ 4cosec ⎜ ⎟ ⎬ (4.4.5)
3 ⎩ ⎝ 2 2 ⎠ ⎝ 2 2 ⎠ ⎪ ⎭

In this figure, when 90 and 0, the total strain
follows from above equation that 1.15. After n
passes, it becomes .
n
n (4.4.6)
n
(2) Ultra-fine grained metal produced by repetitive side
extrusion
(a) Microstructure Figure 4.4.20
From the optical microstructure of metals over 5 TEM micrograph of ultra low-carbon steel after 10 passes
passes of repetitive side extrusion, it has been found of side extrusion.

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