1. For density calculation of twins, it is not appropriate only consider lamellar twins since the corner annealing twin may have only one coherent twin boundary, no matter by which method. With the result of EBSD and TEM, it has been proved the existence of corner annealing twins; therefore, for more accuracy, the density calculation could be derived from EBSD result. Additionally, the method of Na
needs to be modified owing to the volume consideration, which may have some connection to the mechanical property of twins.
2. For the grain orientation, Euler angles are expressed as the orientation matrix which is the rotation from the coordination of crystal to the one of sample. Owing to the 24 symmetry of cubic crystal, there are 24 axis/angle pairs representing the equivalent rotation from crystal to the sample. With EBSD, it is obvious that there could exist multiple twin orientation in a grain, and the misorientation among of them has been approved to be 60° as annealing twinning by the orientation profile of equipment and the calculation from Euler angles.
3. Along the increment of the deformation, more twinning system will be triggered, and thus the intersection of deformations are observed. Because twins are formed by stacking faults and partial dislocations, the interaction of twins may be treated
123
as the interaction of dislocations. With appropriate direction and some external influence, the dislocation will cross-slip through the hindrance; therefore, twins also cross-slip through the other twins and have a slight displacement sometimes.
If the dislocation is obstructed, then the twin will not transmit the other deformation twin.
4. The existence of twins strengthens the mechanical property. However, as a consequence of cross-slip, the hardness at {111/110} interface of twin boundary is lower than at {110/100}, which is the reason for the good ductility of material with twins.
124
Future Work
Based on the previous results, there are some further studies needed to carry on.
1. As mentioned before, grain size does affect the amount of twinning and twinning system; therefore, the compressed α-brass in smaller grain size could be studied in comparison with that in lager grain size in this thesis. Some OMs are shown in Fig.
6-1.
2. Owing to the feature of annealing is not always lamellar, the more accurate twin density would be acquired with accompany of EBSD results.
3. The work of Pande et al. [111] suggests that the annealing twin density is influenced by grain size and there has an maximum value for every material.
Hence, we may calculate twin density in the same grain size in different temperature and observe that if the maxima are the same or close in different materials.
125
(a)
(b)
Fig. 6-1 (a) Undeformed α-brass with smaller grain size.
(b) Deformed 30%.
126
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