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Temperature °C
400
-200
0
200
600
800
Silver
ε
1
10
4
Theoretical shear stress
10
-1
10
3
Dislocation glide
10
-2
10
2
Dislocation creep
10
-3
10
1
Diffusional flow
10
-4
Coble
creep
1
10
-5
Nabarro
creep
10
-1
10
-6
Elastic regime
10
-2
10
-7
10
-3
10
-8
0123456789 0
Homologous temperature,
T
/
T
M
3.17
Deformation mechanism map for pure silver with a grain size of
32 μm and a critical strain rate of 10
−8
s
−1
.
76
transitions from one mechanism to another would occur were determined.
For example in Fig. 3.17, at low temperatures and low stresses, the material
would resist plastic deformation and the material would behave elastically
while in the later modifi cations this low stress regime was considered to be
due to Coble creep.
However, as we continue to increase the temperature and approach higher
homologous temperatures, diffusional processes become dominant. Also
the applied stresses are suffi cient to overcome the fl ow stress corresponding
to that temperature and the material deforms plastically. Since diffusional
creep can either be governed by Coble or N-H creep we fi nd the map out-
lining the regions where these mechanisms are dominant. As Coble creep is
controlled by grain boundary diffusion, it is dominant at lower temperatures
and the Coble creep fi eld lies to the left of N-H creep on the map. Also, if we
increase the stress at a given temperature, dislocation-based mechanisms
come into play. Depending upon the homologous temperature, the defor-
mation can be controlled by dislocation climb or glide. At low homologous
temperatures dislocation climb is suppressed and hence dislocation glide
becomes the dominant deformation mechanism; this is not to be confused
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