**3.3.1 TEM microstructure observations**

274 Recent Trends in Processing and Degradation of Aluminium Alloys

(b)

Fig. 11. AE and force of channel-die compressed Al bi-crystal of {110}<100>/{110}<011> hard/Goss orientation reduced by z≅50%: (a) and corresponding acoustogram (b)

0 500 1000 1500 2000 2500 3000 time [s]

Fig. 12. Behavior of AE and compressive force of bi-crystal of {110}<001>/{100}<011> Goss/shear orientation. The arrows indicate the correlations between AE and drops of force The Goss {110}<001> orientation remained stable during compression in a broad range of deformations, while the shear {100}<011> orientation was strongly unstable and underwent

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The examinations in the micro and mezzo- scale were focused on the structure and texture analyses carried out using transmission (TEM) and scanning (SEM) electron microscopy. In both cases, the observations were correlated with measurements of local orientations changes with the use of *convergent beam electron diffraction* (CBED) and *electron back scattered diffraction* (EBSD) techniques. The TEM orientation measurements were performed using semi-automatic system, while the SEM instrument equipped with field emission gun (FEG) disposed of fully automated system Channe 5TM of HKL Technology firm.

(a) (b)

Fig. 13. Development of dislocation structure observed in TEM in crystallites of Al bi-crystal; (a) and (c) Goss orientation, (b) and (d) shear orientation; total deformation of bi-crystal z≅20%(c) and z≅70%(d). In the Goss orientation traces of planes, on which active slip systems operated are marked

The observations of dislocation structure in TEM in each crystallite of the bi-crystal deformed by z≅20% and z≅70% were correlated with the local orientation measurements in

Mechanical Behavior and Plastic Instabilities of Compressed Al Metals

pair of coplanar systems dominates.

and (b) – reduction z≅63.4%

**3.4 Comparison with other fcc single crystals** 

and Alloys Investigated with Intensive Strain and Acoustic Emission Methods 277

The obtained orientation maps of Goss and shear type presented in Fig. 14 illustrate well the observed tendencies to broadening of the initial orientation of the crystallites in the bicrystal. In the Goss orientation (Fig. 14a), after an applied deformation degree, initial orientation remains stable; only weakly visible tendency to broadening of the {111} plane poles mainly by a rotation around ND is observed. In the case of crystallite of orientation shear (Fig. 14b) a strong tendency to rotation of crystalline lattice through the rotation around TD, towards two complementary positions of the {112}<111> orientation. The presented orientation map shows the structure-texture changes in the area, in which one

In order to document better the correlation between the AE behavior and the localization of deformation connected with twinning processes and the formation of shear bands, experiments at temperature of liquid nitrogen (77 K) were carried out on single crystals of Ag and Cu. The selected results for the Ag single crystals are presented in Fig. 15, and for copper in Fig. 16. The results refer to the same orientation {112}<111> and two subsequent

Fig. 15. Courses of AE and external force and corresponding microstructures of Ag single crystals of orientation {112}<111> channel-die compressed at T=77K: (a) – reduction z≅33%

**shear bands** 

**deformation twins** 

**shear band** 

**steps** 

 **50μm** 

a high-resolution scanning microscope using SEM-FEG/EBSD techniques. The development of dislocation structure observed in TEM is presented in Fig. 13 for each crystallite and for two deformation degrees. The advance of structure refinement together with the increase of deformation was observed in the crystallites with the Goss orientation {100}<011>. In crystallites of shear orientation {100}<011>, two pairs of coplanar slip systems were active what led to the decomposition of the crystal resulting in the change of initial crystallite orientation to two symmetrically situated positions of {112}<111> orientations. The areas, in which different slip systems dominated were separated by intermediate bands.

### **3.3.2 SEM examinations of local texture changes**

The texture-structure examinations were performed using the SEM-FEG/EBSD system at a mezzo-scale, which allows reproducing the "electron" image of structure as regards the crystallographic orientation changes.

Fig. 14. Orientation maps (shown as a "function" of IPF colors) for the part of bi-crystal of Goss (a) and shear (b) orientation and corresponding {111} pole figure. Measurement step 100nm. Reduction z≅20%

The obtained orientation maps of Goss and shear type presented in Fig. 14 illustrate well the observed tendencies to broadening of the initial orientation of the crystallites in the bicrystal. In the Goss orientation (Fig. 14a), after an applied deformation degree, initial orientation remains stable; only weakly visible tendency to broadening of the {111} plane poles mainly by a rotation around ND is observed. In the case of crystallite of orientation shear (Fig. 14b) a strong tendency to rotation of crystalline lattice through the rotation around TD, towards two complementary positions of the {112}<111> orientation. The presented orientation map shows the structure-texture changes in the area, in which one pair of coplanar systems dominates.
