228 Prakt. Met. Sonderband 38 (2006) 
first, when the a grains started to be deformed and fragmented, and the last step when the 
process governed mainly the behaviour of the alpha phase. In Fig. 6b, these two steps can 
be observed. 
The growing of the beta sub-grains at low strain rates was provoked during dynamic 
recovery as reported elsewhere [4,5]. During the deformation, an increment of the density 
of dislocation in the alpha grains located in the B sub-grain boundary occurred. The harder 
alpha phase can pin dislocations. The recovery in the beta phase occurs by a 
rearrangement of the sub-grains and by increasing the size, while the alpha phase 
fragments and globularizes due to the high concentration of dislocations at this phase. 
Fig. 8 shows the orientation of the alpha phase after deformation. Fig 8a) shows the 
distribution of the orientation of alpha grains respect to the plane perpendicular to the load 
for both temperatures at 0.01s™ and 1s™ of strain rate and 0.7 of true strain. Around 80% 
of the alpha grains took an orientation between +40° but the preferential orientation was - 
almost perpendicular to the compression axis as shown in Fig 8b). For values below 0.6 of 
effective local strain, the alpha grains had two preferential orientations: +11 and +23°. an 
orientation of £11 was predominant above 0.6 of effective strain for all the temperature and 
strain rates. 
80 rr pT BE 40 
45 Load én 1“ zo. 
40 e 1s* 
—_ + 768°C 20- 
23 © 0.018" 
* 304 a 1s 10 © De a0 OC mm e me meq. 
‚ 25J = g- —— Bl 
20 a 8 <£ an. CO [0 #0 O00 Mm e =» ou) a 
15+ . 
J . 7 -20 
= 10- . fee 789°C 
5 ; 5 30- 75 0.0187 © 00157 = 
° Q ; BSR I | m is! Oo 4s° 
-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 4 
a) Angle [°] b) Effective Strain 
Fig.8. Orientation of the alpha grains respect to the axis perpendicular to the applied load. Tw 
a)Distribution of the alpha grains in the centre of the specimen. b)Preferential orientation bei 
related to the effective local strain. low 
dis 
To summarize, a comparison of the microstructures in the centre of the specimens Du 
deformed to 0.7 of true strain and at different strain rates with an specimen not deformed pei 
is shown in Fig. 9. At low strain rate, Fig. 9b), the alpha grains became more globular An 
compared to the initial state (Fig. 9a) while the alpha phase was squeezed and elongated du 
at high strain rate (1s™) in Fig. 9 c). du 
5. 
Th 
mi 
bv 
Cr