# Deformation Behaviour of Cold-Rolled Ni/CNT Nanocomposites
## 3 Results and Discussion
### Microstructural Characterization of Cold-Rolled Samples  
The microstructural evolution of the deformed samples is evaluated by unique grain colour maps shown in Figure 4. This figure reveals that the grains elongate in the rolling direction with increasing strain. However, the grains seem more equiaxed for the nanocomposites than for the matrix until 0.36. The grain elongation in the deformation direction is expected and was already mentioned in other authors' works [33]. The hardness evolution is measured to understand this behaviour and is presented in Figure 5. In the case of the Ni matrix, the hardness increases with increasing strain, as expected. However, for nanocomposites, the observed behaviour is different. For strains of 0.11 and 0.22, a softening is observed, and, for higher values, the hardness of the nanocomposites is lower than for the matrix. A more detailed study on the microstructure may explain this behaviour of nanocomposites when subjected to cold-rolling. A more detailed microstructural characterization is carried out on samples of Ni matrix and Ni/CNT nanocomposites cold-rolled up to various strain values. Figure 6 shows maps with the different types of boundaries and grain boundary misorientations' distribution for the Ni and Ni/CNTs samples after deformation. For a strain of 0.11, the Ni matrix and the nanocomposites show an increase in the fraction of CSL and HAGBs and a decrease in the fraction of LAGBs. However, this difference is noticeably more significant for nanocomposites. The Ni matrix cold-rolled with 0.36 is characterized by a high fraction of LAGBs (\(\text{f}_{\text{LAGB}}=70\%\)), a low average disorientation angle (\(\theta_{\text{avg}}=17^{\circ}\)), and elongated grains with a few twins, as can be seen in Figure 5b,e. These effects on the microstructure can be explained by the increase in dislocations necessary to accommodate the imposed deformation, which leads to the formation of dislocation tangles and dislocations walls, which consequently are revealed in the rise in the LAGB fraction. Figure 4: Unique grain colour maps of (**a**,**b**,**c**) Ni and (**d**,**e**,**f**) Ni/CNT samples deformed with strains of (**a**,**d**) 0.11, (**b**,**e**) 0.36, and (**c**,**f**) 0.69. Figure 5: Average microhardness values (HV 0.01) of Ni and Ni/CNT samples after sintering [24], and cold-rolling up to various increasing strains values. Additionally, since the boundaries with lower angle fractions increase, and consequent high angle boundary and CSL decrease, the average disorientation also decreases. For the  
Figure 6: (**–d,g-i**) EBSD maps showing the different boundary types and respective (**–f,j–l**) grain boundary misorientations’ distributions of Ni and Ni/CNT deformed samples with strains of 0.11, 0.36, and 0.69.  
nanocomposites subjected to the same strain, a few different microstructural changes are observed concerning the condition after sintering, with a similar fraction of LAGBs. For the nanocomposites subjected to the same strain, a few different microstructural changes are observed concerning the condition after sintering, with a similar fraction of LAGBs. Regarding the strain of 0.69, the Ni and Ni/CNTs samples are identical. The average disorientation angle decreases with an increasing strain once LAGBs are formed, i.e., the formation of boundaries with lower disorientation causes the decrease in the average disorientation values in the sample, as can be seen in the blue line of the graphs in Figure 3. This effect was also mentioned in the works by [PERSON] et al. [11] and by [PERSON] et al. [33] where, after deformation, a decrease in HAGB was observed accompanied by an increase in the LAGB fraction, leading to a lower average misorientation angle. Although LAGBs are often associated with dislocation cell formation and sub-grain boundaries, a further analysis is performed using estimated GND maps.