**4. Microstructure**

The microstructure of experimental high-entropy alloys was performed selectively by optical microscopy (Olympus GX51 reversed optical microscope) and scanning electron microscopy (Inspect SEM, FEI Company, scanning electron microscope equipped with EDAX Z2e detector) [9, 13–16]. The microstructural aspect of some experimental alloys is shown in **Figures 9**–**14**.

All materials show dendritic formations and interdendritic precipitations in experimental as-cast HEAs. Some of them (HEA 5) shows polyhedral grains and acicular phase growth from the grain boundary (**Figure 9**). The images have been performed for the same magnification (scale of 200 μm). The sample HEA 15 with the highest nickel concentration has the orientation and sequence of the alpha and gamma phases, in the form of parallel or perpendicular planes (**Figure 10**).

Changing the Co content does not make changes to the microstructure, which has a dendritic appearance (**Figure 11**). The increase in chromium content resulted

**149**

**Figure 12.**

**Figure 11.**

*Experimental as-cast AlCrFeCoxNi alloys.*

planes (**Figure 13**) [15].

*Experimental as-cast AlCrxFeCoNi alloys.*

*Characterization and Testing of High-Entropy Alloys from AlCrFeCoNi System for Military…*

in an increased finishing of dendritic microstructure granulation for HEA 36

Scanning electron microscopy images revealed the fine and nanostructured microstructure with polyhedral grains and the layout of phases in quasi-parallel

In the case of high-Ni samples, higher magnification powers can be seen in phase

sample, which also led to an increase in hardness (**Figure 12**).

configurations, in acicular or polymorphic form (**Figure 14**).

*DOI: http://dx.doi.org/10.5772/intechopen.88622*

**Figure 10.** *Experimental as-cast AlCrFeCoNix alloys.*

*Characterization and Testing of High-Entropy Alloys from AlCrFeCoNi System for Military… DOI: http://dx.doi.org/10.5772/intechopen.88622*

**Figure 11.** *Experimental as-cast AlCrFeCoxNi alloys.*

*Engineering Steels and High Entropy-Alloys*

**4. Microstructure**

(**Figure 10**).

ness value was obtained for the sample HEA 36.

sample HEA 38, for minimum concentration of iron.

aspect of some experimental alloys is shown in **Figures 9**–**14**.

30 = AlCr0.4FeCoNi; HEA 31 = AlCr0.6FeCoNi; HEA 32 = AlCr0.8FeCoNi; HEA 33 = AlCr1.2FeCoNi; HEA 34 = AlCr1.4FeCoNi; HEA 35 = AlCr1.6FeCoNi; HEA 36 = AlCr1.8FeCoNi; and HEA 37 = AlCr2FeCoNi. The maximum hard-

The coding of the samples in **Figure 8** was based on the atomic proportions of the chemical elements; thus, HEA 38 = AlCrFe0.2CoNi; HEA 39 = AlCrFe0.4CoNi; HEA 40 = AlCrFe0.6CoNi; HEA 41 = AlCrFe0.8CoNi; HEA 42 = AlCrFe1.2CoNi; HEA 43 = AlCrFe1.4CoNi; HEA 44 = AlCrFe1.6CoNi; HEA 45 = AlCrFe1.8CoNi; and HEA 46 = AlCrFe2CoNi. The maximum hardness value was obtained for the

The microstructure of experimental high-entropy alloys was performed selectively by optical microscopy (Olympus GX51 reversed optical microscope) and scanning electron microscopy (Inspect SEM, FEI Company, scanning electron microscope equipped with EDAX Z2e detector) [9, 13–16]. The microstructural

All materials show dendritic formations and interdendritic precipitations in experimental as-cast HEAs. Some of them (HEA 5) shows polyhedral grains and acicular phase growth from the grain boundary (**Figure 9**). The images have been performed for the same magnification (scale of 200 μm). The sample HEA 15 with the highest nickel concentration has the orientation and sequence of the alpha and gamma phases, in the form of parallel or perpendicular planes

Changing the Co content does not make changes to the microstructure, which has a dendritic appearance (**Figure 11**). The increase in chromium content resulted

**148**

**Figure 10.**

*Experimental as-cast AlCrFeCoNix alloys.*

#### **Figure 12.**

in an increased finishing of dendritic microstructure granulation for HEA 36 sample, which also led to an increase in hardness (**Figure 12**).

Scanning electron microscopy images revealed the fine and nanostructured microstructure with polyhedral grains and the layout of phases in quasi-parallel planes (**Figure 13**) [15].

In the case of high-Ni samples, higher magnification powers can be seen in phase configurations, in acicular or polymorphic form (**Figure 14**).

**Figure 13.** *SEM images of AlxCrFeCoNi alloys.*

**Figure 14.** *SEM images of AlCrFeCoNix alloys.*
