**2.2 Obtaining of AlCrFeCoNi alloy in duplex system including induction and vacuum arc remelting furnace**

A vacuum induction melting-vacuum arc remelting (VIM-VAR) duplex technology was selected to produce the high-entropy alloy AlCrFeCoNi in order to increase the purity of the alloy and to improve its mechanical properties. The experimental batches were prepared in the vacuum induction melting furnace Balzers, HU-40-25- 40-04 type, with a capacity of 12 kg and in the MRF ABJ 900 vacuum arc remelting equipment, both from the ERAMET Laboratory, Bucharest.

The high-entropy alloy used to make the ballistic protection plates in the vacuum induction furnace was produced according to a classical preparation technology, using highly pure materials, and metallic molds made of iron Fc 250 (**Figure 2**) were used for casting to ensure the production of 150 × 100 × 10 mm rectangular plates.

The load calculation (based on the molar mass of the chemical elements, Mmol) for obtaining the Al0.8CrFeCoNi alloy, taking into account the estimated elemental losses, is as follows (Eq. (1)):

$$\mathbf{M}\_{\text{mol}} = 27\mathbf{x}\mathbf{0}.8 + 5\mathbf{2} + 5\mathbf{6} + 5\mathbf{9} + 5\mathbf{9} = 247.6\mathbf{g} \tag{1}$$

The concentration (% weight) of the alloying elements in the alloy was Al = 8.72 wt%; Cr = 21 wt%; Fe = 22.62 wt%; Co = 23.83 wt%; and Ni = 23.83 wt%. The alloy mass calculated based on the volume and density of the alloy cast in a plate and

**Figure 3.**

*HEA Al0.8CrFeCoNi alloy plates obtained by VIM-VAR technology. (a) As-cast HEA samples obtained by VIM technology; (b) HEA sample positioned in copper plate of VAR equipment to be remelted; (c) sample after remelting procedure in VAR equipment.*

related network was 1.111 and 0.574 kg, respectively, resulting in an alloy quantity of approx. 1.6855 kg per ingot.

Since alloy losses occur due to oxidation, due to the interaction with the furnace walls and to the casting ladle, a quantity of 8 kg of prepared alloy is considered per batch.

The quantities of materials used for each batch, also taking into account the oxidation losses, are as follows: Al = 0.74 kg; Cr = 1.70 kg; Fe = 1.85 kg; Co = 1.95 kg; and Ni = 1.93 kg. The total weight of the batch was of 8.17 kg. The Al0.8CrFeCoNi alloy plates obtained by casting are shown in **Figure 3**.

The production of the HEA Al0.8CrFeCoNi plates was completed by refining in the vacuum arc remelting furnace, for which, based on the requirements of the military field, a special copper plate was made, according to **Figure 2b**.

The working procedure in the VAR furnace was classical, seeking the most efficient homogenization of the alloy to ensure the best possible mechanical properties, by remelting each sample three times on each side (**Figure 3c**).
