# Effect of Segregation on Deformation Behaviour of Nanoscale CoCrCuFeNi High-Entropy Alloy
## 3 Results and Discussion
### Tensile Deformation  
Furthermore, modeling the nanoscale CoCrCuFeNi HEA stretching process and the effect of segregation on its mechanical properties were considered. The thickness of the segregated layer was 3 A. The tensile deformation was carried out for a strain value of 15%. Figure 4 shows the dependence of the tensile stress on the magnitude of the applied deformation. The evolution of the structure during the application of the load was accompanied by twinning sharp stress jumps corresponding to the restructuring of the bicrystal structure due to twins. In addition to the twins, the migration of GB near the crack contributed to the development of the deformed structure. The structure with copper segregation with the crack introduced breaks at 4.5% strain, demonstrating the smallest plasticity values within all considered cases. The configurations with nickel and chromium crack + segregation combinations revealed higher plasticity. In these cases, the breaks occurs when the lattice is being deformed to 8.7% and 13.5%, respectively. Nevertheless, the segregation of iron and cobalt and the configuration where the crack was introduced in the initial structure revealed the highest plasticity levels, reaching 15% and above. Figure 5 shows the bicrystal structure with chromium segregation before the break. The common neighbor analysis (CNA) method is used to display structural defects. Amorphous  
Figure 4: The tensile stress–strain curves for the considered bicrystals. The corresponding type of segregated element is indicated in the legend for each bicrystal, while the case without GB segregation is labeled as Bicrystal. The stress drop to zero corresponds to a break in the bicrystal. The considered temperature is 300 K.  
Figure 3: The shear stress–strain curves for the bicrystals with Cr segregation at GB. The corresponding thickness of the segregated layer (1, 3 or 5 Å) is indicated in the legend. The considered temperature is 300 K.  
bridges [39; 40] are clearly visible, which restrain the growing crack and lead to an increase in the plasticity of the bicrystal. The presence of disordered structure (grey area) near the crack indicates that the GBs slide and migrate. The twins are caused by the distortion of the crystal lattice under deformation slide and move throughout the bicrystal. For a more detailed study of mechanical properties under tension, the thickness of segregated layer was increased from 3 A to 5 A. In addition, the structure was deformed by up to 30%. As can be seen from Figure 6, the bicrystal without segregation had the greatest plasticity--it broke when deformed by 16%. The segregation of nickel, cobalt, and iron reduced the plasticity of the bicrystal by 3-5%. The greatest decrease in plasticity was demonstrated by the bicrystals with copper and chromium segregation, the destruction of which occurred when they were stretched by up to 8%. Upon analyzing the dependencies presented in Figures 4 and 6, it was discovered that increasing the thickness of copper and nickel segregations led to a rise in the plasticity of the bicrystal. On the other hand, an increase in the thickness of chromium segregations reduced the plasticity of the bicrystal. Thus, it can be inferred that the strength characteristics of the bicrystal will increase when the thickness of the chromium-segregated layer at the middle GB is increased. This conclusion is in good agreement with the findings in Figure 3, where an increase in the thickness of the segregated layer of chromium resulted in an increase in the maximum shear stress. Figure 7 shows the considered cells of the bicrystals in the process of stretching, before the structures broke. The atoms are colored according to CNA. As mentioned above, structures with the segregation of iron, nickel, and cobalt, as well as a bicrystal without segregation, had the greatest plasticity. These structures have a large number of twin defects.