Prakt. Met. Sonderband 38 (2006) 227 
and after 3.3 DEFORMED MICROSTRUCTURE 
8°C was 
5.7% at The results of the quantitative analysis are shown in Fig. 6 to 8. Fig. 6 shows the mean 
lution of values of the Feret Ratio (Feret Min. / Feret Max.) and the shape factor. The Feret ratio 
riation of gives an idea of the geometrical shape where the value 0 means an ideal line and 1 a 
| perfect circle. The experimental values at low strain rates were higher than the values and 
he alpha 1s! of constant strain rate. 
e shape 0.50 —————— — ——— 0.75 rrr nn Mm 
num and c 786 Diffussion controlled 7 768°C 
788°C. = | © a oO 001s’ 070: process 0 001s’ 
— 19 3 0.45 Oo ___Coarsening al deformation \ 0” 5 
i fo grains: ———— \ 0 -_— 
Mi ea 5 TR yo \ I 
10.8 ar og. a oz ; os 
0.40- 3 > © Ei 
® 9.60 Se u dislocation glide/climb 
06 5 3 8 . Initial an ao process 
© 3 ® © Values i= 
LL } 0357 Elongation of ° = = 0.55 u U © / 
0.48 a grains ——— a . ; be 
ö - 
0.30 ’+1—"+-—7—"75-"7-—+—"7"—7""—1—"—1— 0.50 +—+—+v+—+—F—+"7——71. . iT 5 - 
{0.2 a) 0.0 0.2 04 06 0.8 10 1.2 14 1.6 1.8 b) 0.0 0.2 04 0.6 08 10 1.2 14 1.6 1.8 
Effective Strain Effective Strain 
— 00 Fig.6. a) Feret ratio (Feret Min/ Feret Max.) and b) shape factor as a function of the 
effective strain 
68°C ; . . . . 
Fig. 7 shows the area of the a grains and the ß sub-grains with the effective local strain. 
The o grains decrease with increasing effective strain and decreasing strain rate. An 
increment of the B sub-grain size for low strain rate also was observed. 
: 3.0- —— 3’ —— 
int strain » rr EC 
eak, the 26 o 2] 30- Oo 0.0184 
).01s”, a : . 7 ES 
2 788°C - 788°C _ 
2en both 24 oO 001s’ 5 / Sn o 001s" 
train rate ei? ® is" 20 N » 1s 
5 2.0 nn E 
a < 4 6] Initial SE 
788°C 14 Values a . 
5.| Initial ° ° ue 
1.2 Values 
MO AH ++ 
0.0 0.2 0.4 06 08 10 12 14 16 1.8 00 0.2 04 06 08 10 12 14 16 1.8 
a) Effective Strain b) Effective Strain 
(aD Fig.7. Area as a function of the effective strain of the a) alpha grains, showing a 
decreasing of the size with increasing the effective strain and b) of the beta sub-grains, 
= showing increasing of the size at low strain rates. 
‚18° 
pon The changes of the alpha grains dimensions are related to two main processes during the 
5 07 deformation: the diffusion controlled and the shearing plus dislocation glide/climb 
processes [9]. A separation and globularization of alpha grains was observed at low strain 
rate (0.01s™") due to the diffusion-controlled process, also seen in other works [4, 5]. At 
high strain rates, shearing and the dislocation glide/climb process provoked elongated and 
thin alpha grains, as was also observed in [9]. These processes consisted of two steps: