Electron Beam Surface Treatment and Its Impact on the Plasticity of Fe-Based High-Entropy Alloy

Abstract

In this work, we present results on the impact of electron beam surface modification on the phase composition, microstructure, chemical composition, and mechanical properties of Fe-Ni-Cr-Mo-W high-entropy alloy. During the experiments, the beam power was 600 and 1200 W. The phase composition was studied using XRD measurements. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to analyze the microstructure and chemical composition, respectively. The results showed that at the lower value of the power of the electron beam, a distinguished modified zone cannot be observed. With an increase in the discussed technological parameter, a treated zone with a thickness of about 30 μm can be seen on the top of the sample. The modulus of elasticity on the surface of the unprocessed alloy was measured to be 130 GPa and increased to 156 GPa in the case of both technological regimes of the electron beam surface modification process. The hardness on the top of the untreated alloy was about 4.5 GPa and reduced to about 3 GPa in the case of electron beam treatment on the alloy with a beam power of 600 W. The application of the modification process with a higher value of beam power, 1200 W, led to an even further decrease in the hardness, to about 2.8 GPa. The resistance to plastic deformation of the surface of the considered specimens was also analyzed via the H³/E² ratio, and the results show that the application of the treatment procedure leads to a decrease in the resistance to plastic deformation in both cases. This decrease is more pronounced in the case of the treatment with the higher value of power of the electron beam.

1. Introduction

High-entropy alloys (HEAs) are novel materials that consist of five or more elements with relatively equal or large proportions (usually between 5 and 35 at. %), with much better functional properties in comparison with traditional alloys. The main concept of these types of alloys corresponds with the high entropy of mixing, which is on the basis of, and significantly stimulates, the formation of a single-phase structure, which is stable at room temperature [1]. These alloys could be applied in several modern industrial fields, such as biomedicine, the manufacturing of materials with specific magnetic properties, nuclear industry, heat- and wear-resistant applications, welding production, and manufacturing of superconductors, etc. [2]. It is important to note that high-entropy alloys (HEAs) have shown that significant lattice distortions, caused by differences in the atomic radii of substitutional elements, can lead to the formation of nanostructured and even amorphous phases. These distortions reduce the rate of diffusion, thereby slowing down crystal growth [3,4].

Currently, the improvement of the surface properties of the materials is one of the most studied scientific topics in modern materials science, where a lot of attention has been paid to surface modification by high-energy fluxes (electron and photon beams) [5].

Electron beam surface treatment technologies are highly promising due to their numerous advantages, including exceptional material purity in a high-vacuum environment, short processing times, uniform energy distribution, and high reproducibility of process conditions. These technologies operate by generating thermal gradients from the surface to the specimen’s depth, facilitating rapid heating and cooling during modification. The rates of cooling can reach 10⁴–10⁵ K/s in continuous mode, and up to 10⁻¹⁰ K/s in pulsed mode. This rapid cooling induces phase transformations, preferred crystallographic orientations, and alterations in chemical composition and microstructure, among other effects [5,6,7,8].

Numerous investigations exist exploring the possibilities of improving the functional properties of steels [9,10], titanium-based alloys [11,12,13], aluminum-based alloys [14], and others. The authors of [9] studied the possibility of enhancing the microhardness of 5CrMoMn steel by a treatment using a flux of accelerated electrons. Their results showed a two-fold increase in the discussed mechanical characteristics. Similar research was conducted by Fu et al. [10], where the influence of the electron beam surface treatment of 30CrMnSiA high-strength structural steel on the microhardness and surface roughness was studied. The results reported by these authors showed that the microhardness could be increased by 1.5 times, which was accompanied by a rise in the roughness from 415 to 778 nm. The possibilities of controlling the functional properties of Ti6Al4V titanium alloy by the treatment using a scanning electron beam were studied in Ref. [11]. The results presented in [10] demonstrated a transformation of the microstructure, from double-phase α and β to a single-phase α’ martensitic one, accompanied by an increase in the microhardness by about 25%. Similarly, the author of [12] investigated the effect of the electron beam treatment of TA2 alloy on the microhardness and surface topography and reported an increase in the discussed mechanical characteristic and a decrease in the roughness. Similarly, the results presented in [13] showed an increase in the microhardness of TA15 titanium alloy subjected to electron beam surface modification. Also, Zagulyaev et al. [14] showed the results of the electron beam treatment of Al-Si aluminum alloy. It was found that the hardness and wear resistance were greatly improved after the modification process.

It is important to note that some studies on the modification of HEAs using a high-intensity electron beam, as well as investigations on the effect of the beam treatment on the important structural and functional characteristics of these materials, also exist [15,16,17,18]. The authors of [15] investigated the influence of atmospheric pressure electron beam irradiation of Cr-Mn-V and Cr-Mn-Ti-V high-entropy alloys. Their results demonstrated that the irradiated samples exhibited surface deformation and changes in the crystal orientation and crystallographic texture. In Ref. [16], an AlCrFeCoNi high-entropy alloy was covered by a B+Cr film and subsequently irradiated by the pulsed electron beam. It was shown that the strength and tribological properties were enhanced. Similarly, the results published in Ref. [17] show an improvement in the tribological and corrosion properties on the surface of a CoCrFeNiMo_0.2 high-entropy alloy after irradiation by a high current pulsed electron beam. The authors of [18] investigated the structure and properties of AlCrFeCoNi covered by Cr-B film and modified by a pulsed electron beam and found that boride-based particles have been formed and are responsible for the enhancement of the hardness and wear-resistance.

However, as already mentioned, all these investigations on the electron beam treatment of high-entropy alloys are based on modification in pulsed mode. It is very important to note that the results of the treatment of HEAs by electron beam treatment in continuous mode, as well as information about the processes that occur during the modification procedure, are very limited within the scientific literature. Moreover, experiments based on the electron beam modification of the surface of Fe-based HEAs, and its effect on the plasticity of the alloy, are still lacking in the literature worldwide. Therefore, this study aims to investigate the possibilities of the electron beam surface modification of high-entropy alloy on the system of Fe-Ni-Cr-Mo-W in continuous mode. The results are expected to add new knowledge on the structure formation and changes in the functional properties of important HEAs subjected to treatment by scanning electron beam.

2. Materials and Methods

In this study, an as-delivered Fe-based (Fe-Ni-Cr-Mo-W) high-entropy alloy (27.9 Cr; 2.2 Mn; 35.7 Fe; 30.0 Ni; 3.9 Mo; 0.2 W; 2.1 balance; in wt. %) with a diameter of 20mm and thickness of 4 mm was electron-beam-surface modified using a scanning electron beam (continuous mode). During the modification process, the following technological parameters were used: the acceleration voltage U was 60 kV; the speed of the movement of the samples was 40 mm/s; the scanning frequency f of the electron beam was 1000 Hz; and the electron beam current was 10 and 20 mA corresponding to a beam power of 600 and 1200 W, respectively. During the experiments, the electron beam scanning geometry (beam deflection) was in the form of a line, since following this approach, no overlap of the beam trajectory is realized, leading to higher values of cooling rate (see Figure 1). The whole surface area of the specimen was subjected to the electron beam modification process.

The phase composition and preferred crystallographic orientation of the treated and untreated specimens were investigated by X-ray diffraction. During the measurements, CuKα (1.54 Å) characteristic radiation was used. The experiments were realized in the symmetrical Bragg–Brentano mode, where the step was 0.05°; the counting time was 0.3 s for a step.

The microstructure and elemental content at different points were investigated using a scanning electron microscope (SEM) LYRA I XMU, Brno, Czech Republic, with an integrated detector for energy-dispersive X-ray spectroscopy.

Nanoindentation experiments were conducted to investigate the hardness and Young’s modulus of both modified and untreated surfaces. A Bruker nanomechanical tester (Billerica, MA, USA) was used, with 48 indentations performed on each sample. This study presents the hardness (H), Young’s modulus (E), and resistance to plastic deformation (H³/E²).

3. Results

Figure 2 presents the experimentally obtained XRD patterns of untreated and electron beam-modified Fe-based high-entropy alloys. Figure 2a presents the diffractogram corresponding to unmodified specimen. Figure 2b presents the pattern of the sample subjected to the modification with a beam power of 600 W. Figure 2c corresponds to the specimen modified with the power of the electron beam of 1200 W. The obtained diffractograms show a relatively low background. The diffractograms do not exhibit amorphous-like halos, confirming the higher degree of crystallinity without amorphous inclusions. This means that the application of the electron beam surface modification procedure is not capable of forming any amorphous-like structures within the modified zone. The patterns obtained as a result of the X-ray diffraction experiments are typical for materials with a polycrystalline nature. Peaks corresponding to (111), (200), (220), and (311), belonging to the {111}, {100}, {110}, and {311} families of crystallographic planes, respectively, were detected. These diffraction maxima are typical for the face-centered cubic structure (FCC) of the Fe-Ni-based solid solution. The identification of the experimentally obtained XRD results was performed using the International Center for Diffraction Data (ICDD) database, PDF#47-1417. The results indicate that the phase composition of the Fe-based high-entropy alloy remained unchanged after electron beam modification. Additionally, increasing the electron beam power did not alter the analyzed structural parameter. This suggests that electron beam surface treatment does not affect the phase composition of the Fe-Ni-Cr-Mo-W high-entropy alloy. No significant shifts in peak positions on the 2θ scale were observed, confirming that the lattice parameter and FCC unit cell volume remained unchanged. This is of significant importance for the functional characteristics of the material since the atomic bonds have not been changed significantly concerning the electron beam surface modification procedure [19]. However, the intensities of the experimentally obtained peaks of the untreated alloy and the electron beam processed material are different, meaning that a transformation in the preferred crystallographic orientation occurs as a result of the modification procedure. The crystallographic texture is also of significant importance for the functional properties of the material [20]. This effect is associated with the reorientation of the micro-volumes of the investigated high-entropy alloy. Thus, it is deeply analyzed by the evaluation of the pole density.

The pole density, which is proportional to the probability that a certain family of crystallographic planes is parallel to the surface, is given by Equation (1) [21,22]:

$$P_{\left\{hkl\right\}}={\displaystyle \frac{\frac{I_{\left\{hkl\right\}}^{exp}}{I_{\left\{hkl\right\}}^{stand}}}{\frac{1}{n}{{\displaystyle \sum }}_n\frac{I_{\left\{hkl\right\}}^{exp}}{I_{\left\{hkl\right\}}^{stand}}}}$$

(1)

where P is the calculated value of the pole density (in %); $I_{\left\{hkl\right\}}^{exp}$ and $I_{\left\{hkl\right\}}^{stand}$ are the experimentally obtained intensity of the diffraction maxima and the values available in the ICDD crystallographic database, respectively; and n is the number of the peaks taken into account. The results are presented in Figure 3. Figure 3a corresponds with the calculated values of the untreated specimen. Figure 3b presents the results for the Fe-based HEA processed with a beam power of 600 W, while Figure 3c shows the results for the alloy treated with 1200 W. In all cases, electron beam surface modification induces a transformation in the preferred crystallographic orientation, where the contribution of the {110} family of crystallographic planes becomes much higher. In the case of the untreated specimen, it is only about 5%, while after the application of the modification procedure, the values of P_{hkl} for this family of crystallographic planes exceed 20% at 600 W, and 30% when the beam power was 1200 W. Moreover, the treatment led to a significant decrease in the contribution of {100}, from about 40% in the case of untreated material to less than 16%. Also, it is important to note that the contribution of the {111} family of crystallographic planes increases in the case of the electron beam modification procedure. Before the modification, it was about 16%, while in the case of a treatment using a beam power of 1200 W, it increased to about 20%. Following the results of the contribution of the {311} family of crystallographic planes, a small decrease from about 39% in the case of the unmodified alloy to about 33% in both cases of the electron beam surface modification can be seen. All these features are typical of treated metals and alloys by a scanning electron beam. As already mentioned, the heating and cooling rates are very high and can reach 10⁴–10⁵ K/s in the case of the continuous mode. The modification process redistributes and homogenizes elements on the alloy’s surface, leading to the localized enrichment or depletion of elements that are considered stabilizers of the micro-volumes along different crystallographic directions. This redistribution may explain the observed changes in preferred crystallographic orientation. Furthermore, during the solidification of metals with a cubic crystal structure, grains tend to grow perpendicular to the pool boundaries. This growth direction aligns with the maximum temperature gradient and heat extraction pathway, where the highest degree of undercooling occurs [23]. These process conditions can be defined as strongly non-equilibrium and can be responsible for the formation of crystallographic texture. Similar features were observed by the authors of [24,25], where such a reorientation of the micro-volumes of the electron-beam-processed-Ti-based alloys and the Inconel 625 alloy has been reported.

Figure 2. Experimentally obtained X-ray diffraction pattern of an (a) untreated sample; (b) electron beam-treated specimen with a beam power of 600 W; and (c) electron beam-treated specimen with a beam power of 1200 W [24].

Figure 2. Experimentally obtained X-ray diffraction pattern of an (a) untreated sample; (b) electron beam-treated specimen with a beam power of 600 W; and (c) electron beam-treated specimen with a beam power of 1200 W [24].

To achieve a better understanding of the structure of the as-received and electron beam-modified samples, the lattice parameter of the FCC unit cell and the average crystallite size were evaluated. The lattice parameter was calculated from the XRD results according to the well-known relation between the interplanar distances, given by (2):

$${\displaystyle \frac{1}{d_{hkl}}}={\displaystyle \frac{\sqrt{h^2+k^2+l^2}}{a_{hkl}}}$$

(2)

In Formula (2), d_hkl is the interplanar distance and a_hkl is the lattice parameter of the FCC unit cell. The experimentally obtained results are summarized in

Table 1. Lattice parameter and the average crystallite size of the unmodified and electron beam-treated samples.

Sample	Lattice Parameter (a, Å)	Crystallite Size (D, nm)
unmodified	3.608	22.61
600 W	3.593	26.64
1200 W	3.603	40.10

. Following the values of the lattice parameter a, it does not change. In all considered cases, it is about 3.60 Å with a very small deviation (i.e., the lowest calculated value is 3.593 Å and the highest is 3.608 Å). In all cases, the difference is in the third number after the decimal point, meaning that the discussed structural parameter does not change as a function of the electron beam surface modification using different powers of the electron beam. These findings are in agreement with the results published in Ref. [26]. This means that the atomic bonds have not been changed significantly concerning the electron beam surface modification procedure. Furthermore, it is completely in agreement with the data available in the ICDD (PDF # 47-1417) where the lattice constant is 3.597 Å. It is important to note that the diffraction maxima corresponding to the electron beam processed samples become narrower, pointing towards a reduction in the amount of the crystallographic imperfections (stacking faults, nanopores, dislocations, etc.). As a result of the modification procedure, the surface of the treated samples was heated to a certain temperature. This improved the diffusion of the atoms, which led to a re-distribution and annihilation of lattice defects.

The average crystallite size was calculated from the experimentally obtained XRD results via the Debye–Scherrer equation, which is expressed by Equation (3):

$$D={\displaystyle \frac{0.9\ast \lambda }{\beta \ast cos\left(\theta \right)}}$$

(3)

In Formula (3), D is the crystallite size; 0.9 is a constant related to the particle shape; λ is the wavelength of the X-ray radiation (1.54 Å in the present particular case); β is the FWHM (full width at half maximum) of the considered diffraction maximum; and θ is the Bragg angle. The results obtained are summarized in Table 1. It was demonstrated that the size of the crystallites increased after the electron beam surface modification procedure. The crystallite size of the as-received Fe-based high-entropy alloy was calculated to be about 22 nm and increased to more than 26 nm after the treatment with a beam power of 600 W, and to about 40 nm after the modification using a beam power of 1200 W. This tendency is not typical for electron beam-processed metals and alloys. Generally, the application of such a treatment leads to the refinement of the microstructure, which is not consistent with the results of this study. However, in this case, following the application of a higher-powered electron beam, where the increase in the grain size is more pronounced, the melting of the surface leads to melt homogenization and the dissolution of all kinds of precipitates, and other structural formations within the base matrix of the alloy, which should be considered the reason for the increase in the grain size and volume.

Cross-sectional images obtained by scanning electron microscopy (SEM) are depicted in Figure 4, Figure 5 and Figure 6. A cross-sectional image of unmodified materials is shown in Figure 4. Figure 5 and Figure 6 correspond to the samples subjected to electron beam surface modification with 600 and 1200 W, respectively. Also, the elemental composition at different points, which are shown on the cross-sectional images, was investigated, and the results are presented in

Table 2. Elemental compositions of the unmodified and electron beam-modified Fe-based high-entropy alloy.

Sample	Point	Fe, at%	Ni, at%	Cr, at%	Mn, at%	Mo, at%
unmodified (Figure 4)	1 2 3	37.80 ± 0.38 35.61 ± 0.32 27.93 ± 0.19	29.27 ± 0.23 28.32 ± 0.20 20.28 ± 0.11	27.80 ± 0.19 29.08 ± 0.20 42.29 ± 0.38	3.35 ± 0.01 4.02 ± 0.02 3.92 ± 0.02	1.68 ± 0.01 2.97 ± 0.01 5.58 ± 0.04
600 W (Figure 5)	1 2 3	38.28 ± 0.38 20.83 ± 0.10 14.77 ± 0.06	29.21 ± 0.23 12.05 ± 0.04 6.83 ± 0.03	27.74 ± 0.19 49.80 ± 0.49 70.85 ± 1.13	3.19 ± 0.02 2.97 ± 0.01 3.48 ± 0.01	1.58 ± 0.01 14.35 ± 0.05 4.07 ± 0.04
1200 W (Figure 6)	1 2 3 4	39.49 ± 0.39 34.35 ± 0.31 29.81 ± 0.61 37.59 ± 0.37	30.10 ± 0.24 24.79 ± 0.17 18.53 ± 0.18 27.80 ± 0.22	25.71 ± 0.15 34.61 ± 0.27 45.11 ± 0.36 29.49 ± 0.23	3.73 ± 0.01 5.38 ± 0.03 5.17 ± 0.02 4.00 ± 0.02	0.97 ± 0.01 0.88 ± 0.02 1.38 ± 0.01 1.12 ± 0.01

. The microstructure of the unmodified alloy consists of a base Fe-Ni matrix and homogeneously distributed precipitates within it, with an irregular shape. Also, a large number of pores can be seen within the whole volume of the sample. The results achieved after the performance of the EDX experiments confirmed that the base matrix is composed mostly of Fe and Ni, where some amount of Cr also exists. However, the amount of Fe and Ni within the precipitates is reduced. Considering the elemental composition of the precipitates, they consist of brighter and darker regions (see points 2 and 3 in Figure 4). The EDX results show that the Cr content increases in the precipitates, where this increase is much more pronounced within the dark region (point 3).

The cross-sectional microstructure of the electron beam-modified alloy with a beam power of 600 W (Figure 5) again represents a base matrix consisting mostly of Fe and Ni with some amount of Cr content and irregularly shaped precipitates homogeneously distributed within the base material. No change in the microstructure can be seen as a result of the electron beam modification using a beam power of 600 W. Also, some pores can again be seen within the whole volume of the alloy. Using these technological conditions, the modified surface was just irradiated without the formation of a melted zone and dissolution of the precipitates. As mentioned previously, at the electron beam modification technologies, the kinetic energy of the negatively charged particles transforms to heat [27]. However, in this case, the temperature on the surface of the sample was not high enough for melting. The results of the EDX experiments again show that the formed precipitates are much richer in Cr in comparison with the base Fe-Ni matrix. These results point out that the application of the modification procedure using the aforementioned process parameters and a beam power of 600 W is insufficient to induce a transformation in the microstructure of the investigated alloy. However, they can induce the redistribution of the elemental composition and, as a result, the Cr content within the precipitates can become much higher in comparison with the base matrix.

Figure 6 shows the cross-sectional microstructure of the alloy modified with a beam power of 1200 W. It can be clearly seen that a distinguished surface-modified zone has been formed as a result of the modification procedure. It is marked as zone A, while the base alloy matrix is marked as B. The thickness of the surface-modified zone is about 30 μm. Its microstructure comprises the base Fe-Ni alloy matrix, and no precipitates can be seen within it. Also, no pores, cracks, or other imperfections can be detected within the modified surface. Below this zone, the microstructure is in the form of the base Fe-Ni matrix, and randomly distributed precipitates and pores can be observed, which is typical for this Fe-based high-entropy alloy. These results confirm that modification with a scanning electron beam with a beam power of 1200 W, and the technological conditions mentioned in the second part of this article (Section 2), are appropriate for forming a surface-modified zone with a lack of precipitates. According to the authors of [28], a higher value of the beam power leads to an increase in the surface temperature. During the modification procedure, the temperature on the surface was already enough to melt the surface, and the precipitates were dissolved. Also, the elimination of the pores is typical for the electron beam-processed materials, and has also been observed by the authors of [20]. During the modification process, where the treated surface is in a molten state, a large thermal gradient exists and is responsible for the formation of strong convection flows, which are known as Marangoni flows or Marangoni convection. These flows are responsible for the removal of the pores and other structural imperfections [20].

The mechanical properties of the Fe-based high-entropy alloy were studied in terms of hardness, Young’s modulus, and resistance to plastic deformation (H³/E²). The experiments were performed by way of nanoindentation tests, following the method of Oliver Pharr [29,30]. The results are presented in Figure 7 and Figure 8 and

Table 3. Mechanical characteristics of the unmodified and electron beam-treated samples.

Sample	H, GPa	E, GPa	H3/E2, GPa
unmodified	4.45 ± 0.79	130.228 ± 13.296	0.0050
600 W	3.03 ± 0.58	156.215 ± 15.240	0.0010
1200 W	2.84 ± 0.46	156.373 ± 30.772	0.0009

. Figure 7 shows the hardness (H) and Young’s modulus (E). The hardness of the unmodified alloy is about 4.5 GPa. The application of the modification process led to a decrease in the discussed mechanical characteristic to about 3 GPa at a beam power of 600 W. The application of the higher value of the power of the electron beam led to a further decrease to about 2.8 GPa. It can be concluded that the application of the electron beam modification procedure led to a decrease in the hardness, where in the case of the higher value of the power of the electron beam, the reduction in this mechanical characteristic was about 2-fold. The Young’s modulus of the unmodified alloy was more than 130 GPa, and increased to about 150 GPa in both considered cases of modification of the alloy using a scanning electron beam. These features could be attributed to the reorientation of the micro-volumes of the base material, as well as the dissolution of the Cr-rich precipitates when modification with 1200 W was conducted. As stated previously, the contribution of the {111} family of crystallographic planes decreases by about 5%, which could be considered a prerequisite for the decrease in the hardness of the sample processed by a scanning electron beam with the power of the electron beam of 600 W. Considering the specimen modified using the higher value of the beam power, the contribution of the {111} family of crystallographic planes is about 20%, which is the highest value among the samples considered in this study. However, the dissolution of the Cr-rich precipitates within the base Fe-Ni matrix should have a major influence on the mechanical properties and should be responsible for the reduction in the discussed mechanical characteristic.

The plasticity was presented by the H³/E² ratio, pointing to the resistance to plastic deformation, where lower values of this ratio could be associated with better plasticity, which means that the material could undertake permanent shape change (i.e., plastic deformation) without breaking. This ratio directly signifies the resistance to plastic deformation [31,32], and the results are summarized in Table 3 and are illustrated in Figure 8. The results obtained in the present study show that in all considered cases of the surface modification of the Fe-based high-entropy alloy using the scanning electron beam, the H³/E² ratio decreases, pointing to a decrease in the resistance to plastic deformation. This value for the unmodified specimen is 0.0050 GPa. In the case of the modification using a beam power of 600 W, it decreases significantly to 0.0010 GPa, and further decreases to 0.0009 GPa when modification with 1200 W was applied.

The load–displacement curves of the untreated and electron beam-modified alloys are depicted in Figure 9. Figure 9a presents the curve of the unmodified material. Figure 9b shows the curve of the modified alloy using a beam power of 600 W. Figure 9c presents the curve of the modified material with a beam power of 1200 W. According to the authors of [33], the load vs. displacement curve is essentially a unique identifier for a material’s mechanical behavior, capturing how it responds to applied forces. The elastic region represents the reversible deformation, where the material returns to its original shape once the load is removed, while the plastic region indicates permanent deformation. The plastic work (W_p) and elastic work (W_e) done are indicated in Figure 9. The plastic work done is much greater in the case of a treatment of the alloy with a scanning electron beam. As already mentioned, plasticity and plastic deformation are key indicators of a material’s ductility. Brittle materials, by contrast, cannot undergo plastic deformation, significantly restricting their range of applications. In metals and alloys, improved plasticity not only enhances their formability, but also contributes to better damping properties, making them more effective in energy absorption. Additionally, increased plasticity at the surface reduces crack formation and initiation, which is crucial for durability in various industrial applications. These advancements could extend the practical uses of the discussed metallic materials and unlock new possibilities for innovative applications across multiple industries.

4. Discussion

This work presents results on the influence of a surface modification procedure by a scanning electron beam of Fe-based high-entropy alloy on important mechanical properties. The effect of the power of the flux of accelerated electrons on the hardness, Young’s modulus, and resistance to plastic deformation was investigated, whereas the values of 600 and 1200 W were considered the most representative. It was shown that the studied mechanical characteristics decreased as a result of the modification process. The reduction in the H³/E² ratio (i.e., the resistance to plastic deformation [31,32]) was considered very important, since it means that the plasticity on the surface of the alloy, where it is mostly explored for exploitation, was improved. As was already stated, the improved plasticity not only enhances their formability, but also contributes to better damping properties, making them more effective in energy absorption. Additionally, increased plasticity at the surface reduces crack formation and initiation, which is crucial for durability in various industrial applications. The crystallographic structure is of significant importance for the determination of the plastic properties of metals and alloys. The plastic deformation is realized by the slipping and distribution of the dislocations, which occurs in a specific slip system, defined by a set of crystallographic planes and their corresponding directions. For the plastic deformation of metallic materials without fracturing and formation of cracks, at least five independent slip systems are needed. In this sense, metals and alloys with face-centered cubic structures (FCC) are characterized by excellent plasticity, since this structure is characterized by 12 systems of slipping, which are independent. As reported above, the modification of the surface of the Fe-based high-entropy alloy resulted in a transformation of the preferred crystallographic orientation. The dislocations’ mobility along the newly formed crystallographic planes and their corresponding directions should increase, leading to enhanced plasticity. From another perspective, the plastic properties of metals and alloys are affected not only by the crystallographic structure and preferred crystallographic orientation, but also by the microstructure of the material. As stated above, plasticity is closely linked to dislocation slip, and any obstruction to dislocation movement can reduce it [34,35]. Hard precipitates and other microstructural features can hinder dislocation mobility, thereby limiting plastic deformation. Consequently, microstructures containing precipitates that obstruct dislocation motion are expected to exhibit reduced plasticity. These statements fully meet the results of our investigation. It was demonstrated that the resistance to plastic deformation of the specimen processed by a beam power of 1200 W has the lowest value among all considered samples. As mentioned previously, the application of these technological conditions is capable of eliminating the precipitates, which should be considered a barrier to the distribution of the dislocations.

The findings of this study demonstrate that electron beam surface modification technology can significantly enhance plasticity and plastic deformation. This improvement corresponds to increased damping properties and a substantial reduction in crack formation and initiation. These findings represent a significant practical improvement. Damping refers to the conversion of oscillation energy into other energy forms, which is very important for addressing noise and vibration issues in industrial applications. One effective approach involves materials with structures and phase compositions that enable the absorption of dissipative energy. A popular method for the formation and application of high-dampening alloys is their application in the form of thin films and coatings. For example, Abuova et al. [36] have studied the effect of applying TiN-Cu coatings on the dampening properties of Cr-Ni-V steels. The coatings were formed using a high-vacuum arc plasma spraying method. As a result of their work, the dampening properties of the investigated samples improved significantly due to the unique structure of the formed coatings that propagated the mobility of dislocations, although still pinning some of them, resulting in a loss of energy. Recently, the improvement in the dampening of nickel foams has also been investigated by applying graphene coatings using chemical vapor deposition by the authors of [37]. They found that only 0.24 wt% of a graphene coating can significantly reinforce and improve the dampening properties of the nickel foams, with the vibration dampening ration being improved by over 50%.

The methods implementing the use of surface coatings for damping purposes have been proven to be a great success; however, they induce some problems that need to be addressed. Firstly, the quality of the coating depends entirely on the deposition technique. Each of these coatings have their own specifications, characteristics, and limitations. Secondly, the interaction (adhesion) between the substrate and the coating needs to be precisely controlled in order to obtain coatings with the best possible strength. While applying coatings, internal stresses also occur, which also need to be considered. The non-uniformity of the applied coatings and their properties would undoubtedly lead to variable properties of the output samples, as proven by Torvik et al. [38]. Regardless, all of these specifics also allow for the successful research and development of new compatible materials with improved properties.

As a supplement to methods utilizing the application of coatings, the current work demonstrates an alternative method for the modification of the dampening properties of materials. The alloy examined in this study exhibits high damping capacity due to its structural characteristics, namely the decontextualizing of the crystal orientation of the formed surface layers after the electron beam treatment, and also the transformations occurring in the solid solution. Evidently, the highest degree of transformation and decontextualization of the samples was achieved by using a beam power of 1200 W, where the heat generated was great high enough to cause partial melting of the surface of the sample. The investigated alloys combine exceptional damping properties with high strength and plasticity, which were further improved during the current investigation. Additionally, as noted by the authors of [39], lower H³/E² values indicate increased energy dissipation, enhancing the damping performance even more. The obtained results could find applications across various modern industries, including aerospace, automotives, electrical engineering, and others. Of course, it is highly important to note that the application of a complex electron beam setup needs to be justified by the imposing need of the users and manufacturers on an economical scale.

5. Conclusions

This study shows the possibility and effect of the modification of Fe-based high-entropy alloy using a scanning electron beam on the phase composition, the formation of a preferred crystallographic orientation, and important mechanical properties, such as hardness, Young’s modulus, and resistance to plastic deformation. The power of the electron beam was 600 and 1200 W. The following conclusions can be drawn:

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The phase composition of the Fe-based high-entropy alloy is in the form of a face-centered cubic structure. The application of the modification using a scanning electron beam did not affect the phase composition of the samples. However, a transformation in the preferred crystallographic orientation was established as a result of the modification procedure.

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The microstructure of the Fe-based high-entropy alloy is in the form of Cr-rich precipitate homogeneously distributed within the Fe-Ni matrix. The application of the lower value of the power of the electron beam of 600 W did not affect its microstructure. However, with the application of 1200 W power, a clearly separated modified zone was formed without the existence of Cr-rich precipitates.

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The electron beam surface modification procedure led to a decrease in the hardness and an increase in Young’s modulus. The resistance to plastic deformation (H³/E²) decreases as well, which is expected to have advantages from a practical point of view.