Tuning Dielectric Properties of Ti-6Al-4V Powders with B₄C and TiC via Ti⁴⁺ Electron Binding Energy Optimization

Abstract

In this study, Ti-6Al-4V (TC4) powder was uniformly mixed with B₄C and TiC, respectively. Subsequently, the dielectric properties of the B₄C/TC4 and TiC/TC4 composite powders were measured. Meanwhile, XPS analysis was used to deeply analyze different atoms in these samples to obtain the electron binding energy data of each atom. The experimental results show that even when there is no phase structure transformation between B₄C, TiC, and TC4, the dielectric coefficient of the composite powder and the electron binding energy values of various elements still exhibit significant changes. When the mass ratio of B₄C or TiC to TC4 reaches 1:30, the dielectric constant of the composite powder is significantly increased from 5 (the original TC4) to about 11 and 15, respectively. At the same time, the electron binding energy of the Ti element in TC4 also reaches the maximum value. In addition, due to the difference in electronegativity between B₄C and TiC, during the process of compounding with TC4, the incorporation contents and the occurrence frequencies of abnormal dispersion phenomena are different. Specifically, when the ratio of B₄C to TC4 is 1:30, abnormal dispersion occurs at a frequency of 9.5 GHz; however, when the ratio of TiC to TC4 is 1:20, the composite coating shows an abnormal dispersion phenomenon at 8.5 GHz.

1. Introduction

Since the 1980s, with the rapid development of advanced aircrafts, the service performance requirements for air vehicle components and their supporting materials have been increasing [1,2]. The element titanium (Ti) and Ti alloys have the advantages of low density, high specific strength, corrosion resistance, and high temperature resistance [3]. The applications of both Ti and Ti alloys in advanced air Fighters (F-22) has been steadily increasing to a prevalence of more than 40% [4]. To implement further improvements in strength, many researchers have introduced the concept of Ti matrix composites (TMCs) by adding ceramic-reinforcing phases during the material preparation process, and utilizing strengthening mechanisms such as pinning movable dislocation, limiting grain rotation, and so on. Fereiduni et al. [5] demonstrated that by adding a small amount (0.2 wt.%) of B₄C to the Ti-6Al-4V (TC4) alloy, the yield strength and ultimate compressive strength of TMC were enhanced. Compared with other particulate ceramic-reinforcement materials, TiC has a higher stability and compatibility. When the size of TiC particles reaches the nanometer scale, the interaction between particles and dislocation becomes significant, resulting in enhanced strength. Markovsky [6] made bilayer structures of the TC4 alloy and its composites with TiC or TiB. The deformation and damage process of the bilayer alloy/composite were carefully studied.

Since the fourth generation of aircraft, stealth performance has become a key indicator of advanced military aircraft. Improving the electromagnetic absorption performance of the fuselage, engines, and other key components to reduce the radar reflection area has become the focus of research and development. For components made of Ti-based materials, improving the wave-absorbing properties while maintaining the mechanical performance is a great challenge. A “structure–function integration” material design strategy is being pursued to address this issue. It has been observed that TiC has a high dielectric constant; by adjusting the ratio of TiC to paraffin and epoxy, the dielectric constant can be varied from 2 to 65 [7], enhancing the electromagnetic wave impedance of the material across different frequency bands, and ultimately affecting the reflectivity of the electromagnetic wave. Additionally, some studies show that the use of B₄C with different particle sizes can effectively adjust the interface between the matrix and the B₄C-reinforced phase [8], thus improving its space charge polarization ability and the dielectric properties of the sample.

Previous studies on enhanced TMCs, such as B₄C and TiC, have mainly focused on mechanical properties, with few reports on electrical properties and microscopic mechanisms. In this research, we prepared B₄C/TC4 and TiC/TC4 composite powders via ball-milling; tested their dielectric properties; explored the internal polarization mechanism; and, from the electronic structure change perspective, revealed how different B₄C and TiC contents affect the composite powders’ dielectric properties.

The selection of B₄C and TiC to adjust the dielectric coefficient is well grounded. Ample studies have shown that during additive manufacturing, the mixture of B₄C and TC4 powders can produce some TiB and TiC, greatly enhancing TC4’s mechanical properties. According to the capacitor interface theory, for materials with different electrical conductivities, due to the difference in charge-binding ability at the interface, high polarizability occurs, changing the material’s dielectric coefficient and optimizing its dielectric properties. B₄C is chosen because during additive manufacturing, though part of it reacts with TC4 to form TiB and TiC, most can still form many heterogeneous interfaces with TC4, making it crucial to study B₄C-TC4 mixtures with different contents to explore the dielectric coefficient variation rules. In addition, as TiC has a high electrical conductivity, while TC4 has a relatively low conductivity among metal materials, the heterogeneous interface formed between them is likely to have a significant impact on the material’s dielectric properties; thus, in-depth research is necessary.

2. Experiments

B₄C, TiC, and TC4 (purity = 99.99%) were mixed according to the ratios in

Table 1. Sample names and their composition.

Sample Name	TC4 (g)	B4C (g)	TiC (g)	TC4:B4C or TiC
TC4	10.0			--
B4C		10.0		--
BC-1	9.9	0.1		100:1
BC-3	9.7	0.3		30:1
BC-5	9.5	0.5		20:1
BC-10	9.0	1.0		10:1
TiC			10.0
TC-1	9.9		0.1	100:1
TC-3	9.7		0.3	30:1
TC-5	9.5		0.5	20:1
TC-10	9.0		1.0	10:1

. In order to eliminate the formation of new substances, the different proportions of the powders were mixed homogeneously via ball milling. The particle size and morphology of the powders were observed using secondary electron imaging of scanning electron microscopy (SEM, ZEISS-Ultra Plus, Göttingen, German) at an electron accelerating voltage of 15 kV.

The QM-3SP4 planetary ball mill was employed to blend TC4 powder with B₄C particles under an argon atmosphere. The rotational speed was set at 250 rpm for a mixing duration of 2 h, and no grinding balls were used in the planetary mill.

The mixed samples were characterized using X-ray diffraction (XRD, SmartLab, Rigaku, Japan), with a scan rate of 3°/min, a scan range of 10–85°, and a step size of 0.02, Cu-Kα. X-ray photoelectron spectroscopy (XPS, AXIS UItraDLD, Shimadzu, UK) was used to observe the electron binding energy of the elements in the B₄C/TC4 and TiC/TC4 samples, and Al-Kα was used as the electron beam source. The XRD and XPS spectra were normalized to allow for a further discussion of the crystalline or electronic structure in relation to the diffraction peaks and binding peak intensity. The dielectric properties of the samples were measured using a vector network analyzer (VNA, N5230C, Agilent, CA, USA) in the frequency range of 2–10 GHz using the standard 3.5 mm coaxial method.

3. Results and Discussion

Figure 1 presents the morphologies of the three powder samples. B4C manifests a lamellar structure, with a size ranging approximately from 5 to 10 μm (Figure 1a). TiC has a relatively smaller particle size, measuring 200–300 nm (Figure 1b), while TC4 has a particle size of 100 μm (Figure 1c). Figure 1d,e display the morphologies of the ball-milled TiC/TC4 and B₄C/TC4 composites, respectively. After refinement, the B4C and TiC powders exhibit reduced mobility and enhanced viscosity. This change enables them to bond more effectively with the TC4 particles. The substantial difference in particle sizes between B₄C, TiC, and TC4 renders it extremely difficult to concurrently observe the microstructures of B₄C and TiC together with TC4 at a single scale. Nevertheless, as is evident from Figure 1d,e, both B₄C and TiC can uniformly adhere to the surface of TC4. Consequently, the spherical TC4 particles are evenly coated with a layer of either B₄C or TiC.

3.1. B₄C/TC4 Mixing

Figure 2 shows the XRD spectra of the samples. As indicated, both the B₄C and TC4 samples consist of pure powder. After mixing, the B₄C/TC4 composite powder consists of the diffraction peaks of both B₄C and TC4, and the intensity of B₄C diffraction peaks increases as the content of B₄C increases. Except for the diffraction peaks of TC4 and B₄C, no other diffraction peaks are observed from BC-1 to BC-10, demonstrating the absence of impurity phases or new compound formation during the mixing process.

Figure 3 shows the XPS spectra of different B₄C/TC4 samples. The electronic structure of Ti elements that can be detected is mainly 2p electron spectral lines, which exist in two binding forms in TC4. One is the combination of elemental Ti and p electrons with a binding energy of 453.9 eV, and the other is the combination of TiO₂ with a binding energy of 458.3 eV. Although the O element does not exist in TC4, when compared to elemental Ti, the binding form between Ti atoms in TC4 is more complex. The arrangement includes a two-phase interface and dislocation, while the Al, V, and other elements are solvable between Ti atoms. As a result, the electron cloud around the Ti atoms in TC4 is completely different from that of pure Ti. According to the discussion in [9], it can be concluded that the Ti atom in TC4 has a higher potential energy and a strong ability to attract electrons, leading to a lower initial kinetic energy of electrons and a stronger electronegativity in electron distribution. The Ti atom in TC4 exhibits a higher TiO₂ spectral line intensity than pure Ti, resulting in a certain electronegativity in the electron cloud distribution around the Ti atom in TC4. Additionally, the lower spectral line intensity of Ti 2p_3/2 in TC4 makes it challenging to observe the electron binding spectral line of Ti 2p_1/2.

As the Ti 2p (TiO₂ form, a form of annotation, the material does not contain TiO₂) binding spectral line is the primary binding form of the Ti element in TC4, the distribution of the binding spectral line of Ti 2p_3/2 (TiO₂ form, hereinafter referred to as Ti 2p_3/2) is detailed in Figure 3b. It can be observed that the binding energy corresponding to the Ti 2p_3/2 spectral line in the pure TC4 sample is 458.3 eV. When the content of B₄C and TC4 is lower than 1:30 (i.e., BC-1 and BC-3), the binding energy of the Ti 2p_3/2 spectral line increases with the increase in B₄C content. Specifically, the binding energy of the Ti 2p_3/2 spectral line of BC-1 is 458.6 eV, and that of BC-3 is 458.7 eV. However, with the further increase in B₄C content, the binding energy corresponding to the Ti 2p_3/2 spectral line begins to decline. The corresponding binding energy of the Ti 2p_3/2 of BC-5 and BC-10 is 458.4 eV and 458.5 eV, respectively. With the increase in the content of B₄C, the electron binding energy is shifted towards an increase in binding energy. The numerical changes show that when B₄C powder is added, even if there is no change in lattice structure, B₄C can still have a certain effect on the electrons around Ti atoms in TC4. Combined with the results of Figure 1, B₄C is a lamellar structure, and its own structure also leads to the uneven distribution of electron clouds around B atoms and C atoms, i.e., the phenomenon of polarization exists. When the ratio of the two is lower than 1:30, a small amount of layered and polarized B₄C can attract electrons around Ti atoms, which increases the average electron potential energy in some parts of TC4. This results in the electronegativity of Ti 2p electrons further increasing and the electron cloud density around some Ti atoms further decreases. As a result, the binding energy increases, and the initial kinetic energy obtained by electrons decreases [10]. However, when the content of B₄C is further increased, the distribution of B₄C becomes more uniform, leading to a decline in the ability to induce the electron cloud migration of Ti atoms in TC4. Therefore, for elemental Ti, its own oxidation ability is weakened and the electron cloud distribution is nearly uniform.

Since Al and V in TC4 are solidly dissolved in the Ti matrix as intermediate phases of Al-V alloys, the XPS peak intensities for both Al and V are weak. Figure 4a,b show the binding spectra of Al and V, respectively [11], with no distinct binding peak observed due to the low V content. According to Figure 4a, there are only two forms of binding energy for Al at ~74.2 eV. Therefore, it can be inferred that the electron cloud around Al is not changed by the doping of B₄C. In addition, due to the low intensity of the Al2p_3/2 spectral line, no electron binding spectral line of Al2p_1/2 is observed.

The binding energy spectral lines of elements C and B in B₄C are shown in Figure 5. In Figure 5a, it can be observed that the electron spectral lines of C1s in elemental C have the highest intensity at 285.1 eV, where there is a chemical shift towards an increase in binding energy between samples BC-1 and BC-3. This indicates that in the BC-1 and BC-3 samples, there is an increase in the positive ion energy around the C atom, resulting in stronger electron binding. Additionally, the electron spectral lines of C1s of BC-1 and BC-3 exhibit an asymmetric trend, which also suggests that the incorporation of a small amount of B₄C into TC4 leads to a tendency for the electrons around the C atom to transition into metallized electrons, thereby enhancing the electronegativity of the electrons surrounding the C atom. However, with a further increase in the B₄C content, the C1s line of the C atom returns to 281.5 eV. This suggests that the increased B₄C in the BC-5 and BC-10 samples makes the distribution of B₄C in TC4 more uniform, thus weakening the electronegativity of electrons surrounding the C atom. In addition, for the C atom in B₄C, there are still C1s electron spectral lines at 281.7 eV and 288.9–289.5 eV, which means that there are two other electron ground-state binding forms between the B and C atom. At 281.7 eV, the intensity of the C1s binding spectral line in B₄C is the highest, and with the increase in B₄C content, the intensity of the C1s spectral line decreases. A similar phenomenon can be observed at 288.9–289.5 eV. This indicates that when the C atom in B₄C is mixed with TC4, the increase in its proportion will decrease the electron state density between the B and C atoms. This means that the electron segregation will occur, which will have a greater impact on the electronic polarization of B₄C. For atom B, as shown in Figure 5b, no significant difference is found in the value and intensity of its electron binding energy. Therefore, for the mixing of B₄C and TC4, only the distribution of electron clouds around atom C changes greatly.

Figure 6a presents the dielectric properties of different samples. Figure 6a shows the real part of the dielectric constant. In the frequency range of 2–10 GHz, significant differences can be observed in the dielectric constants of various materials. The dielectric constant of TC4 is the lowest, at approximately 5, while that of B₄C is the highest, at around 11. When B₄C is added to TC4, with the gradual increase in the B₄C content, the dielectric constant of the composite material changes significantly. For example, the dielectric constant of BC-1 rises to 8, and reaches its peak value in BC-3, ranging from 9 to 11. However, when the B₄C content is further increased to prepare the BC-5 and BC-10 samples, the dielectric constant drops to approximately 5.5.

Based on the research conclusions of Figure 3b and Figure 5a, B₄C has a strong electronegativity. When the B₄C content is low, due to its thin thickness attached to the surface of TC4, the TC4 particles in BC-1 and BC-3 also exhibit strong electronegativity. The interface between B₄C and TC4 promotes the formation of polarization at the spherical interface. This polarization increases the electron binding energy value of the Ti atoms in TC4, resulting in a stronger ionic polarization ability of the Ti 2p electrons in TC4, ultimately leading to a relatively high dielectric constant. In the BC-3 sample, the electron binding energy of Ti 2p3/2 reaches its maximum, indicating that at this ratio, the polarization rate of the interface between B₄C and TC4 is the highest; therefore, the dielectric constant is also the highest. With the further increase in the B₄C content, the thickness of the B₄C layer increases, and its own electronegativity decreases accordingly. As a result, the polarization ability at the interface between B₄C and TC4 begins to decline, and the electronegativity of the Ti 2p electrons in TC4 also weakens. Therefore, the dielectric constants of BC-5 and BC-10 decrease.

Figure 6b shows the imaginary part of the dielectric constant of each sample. It can be seen from the figure that B₄C has a relatively high imaginary part value of the dielectric constant in the frequency range of 2–8 GHz, at approximately 1.5–2, indicating that there is a relatively obvious dielectric loss in B₄C. Near 8 GHz, the real part of the dielectric of B₄C decreases significantly, while the imaginary part shows a distinct peak. This phenomenon indicates that B₄C exhibits an abnormal dispersion phenomenon at this frequency, and the loss reaches its maximum value at this time, meaning that the electrons in B₄C have a special resonance frequency in this frequency band.

For the BC-3 sample, due to the strong polarization ability at the interface between B₄C and TC4, as well as the resonance frequency of electrons in B₄C at 8 GHz, in the frequency range of 7–9 GHz, under the combined action of these two factors, both the real part and the imaginary part of the dielectric of BC-3 increase. This indicates that resonance occurs between electronic polarization and the interface polarization of B₄C/TC4 in the BC-3 sample. When the frequency exceeds 9 GHz, the real part of the dielectric of the BC-3 sample begins to decline, while the imaginary part continues to increase, triggering a relaxation phenomenon, and the dielectric loss reaches its maximum.

In the BC-1 sample, the real part of the dielectric is lower than that of the BC-3 sample, which means that the interface polarization ability of BC-1 is weaker, and the dielectric loss is lower compared with the BC-3 sample. In addition, no resonance phenomenon is observed in the BC-1 sample, indicating that adding different contents of B₄C can change the natural frequency of electrons in TC4. In BC-5 and BC-10, due to the further weakening of the polarization ability at the B₄C/TC4 interface, there is no electron resonance and dielectric relaxation phenomenon near 8 GHz, indicating that the polarization strength of B₄C has an impact on the natural frequency of electrons. In addition, compared with the BC-3 sample, the interface polarization ability of BC-5 is weakened, but dielectric loss still occurs in the low-frequency range of 2–4 GHz. This means that adding B₄C to TC4 can induce a new relaxation polarization phenomenon in TC4. By controlling the content of B₄C, new forms of polarization loss can be induced.

In summary, after the simple mechanical mixing of B₄C and TC4, by controlling the content of B₄C, the polarization rate of B₄C/TC4 can be changed, thereby adjusting the natural frequency of electron resonance in B₄C. This enables B₄C to resonate with the interface of TC4 at different frequency bands, triggering dielectric loss. When the ratio of B₄C to TC4 is 1:30, the electron binding energy of the 2p electrons in the Ti atoms is the largest. At this time, the electronegativity of the electron cloud distribution is enhanced, and the dielectric constant is larger.

3.2. TiC/TC4 Mixing

Figure 7 shows the XRD patterns of TiC and TC4 at different ratios. According to the PDF cards, the results are consistent with the B₄C mixing results. TiC and TC4 are pure sample powders, and after mixing, as the content of TiC increases, the diffraction peak intensity of TiC in the samples also gradually increases. Additionally, except for the diffraction peaks of TC4 and TiC, no other diffraction peaks were observed in TC-1–TC-10. This also demonstrates that there is no lattice translation or other components in the TiC/TC4 mixing process.

The XPS spectral lines of Ti atoms with different TiC contents are shown in Figure 8a–c. From the total XPS spectrum of Ti in Figure 8a, it can be seen that a group of binding spectral lines of Ti 2p_3/2 appear at 454.9 eV. After a comparison with the results in Figure 2, it can be concluded that the binding spectral line here is the Ti element in TiC. Figure 8b shows the enlarged figure of the spectral line. When a small amount of TiC was incorporated into TC4 (TC-1 sample), the strength of the binding spectral line of Ti 2p_3/2 (TiC class) decreased, which was consistent with the result of doping B₄C. With the addition of TiC, the binding energy of Ti 2p_3/2 (TiC form) also showed a chemical shift, increasing by 0.5–0.7 eV. The binding energy value of the Ti 2p_3/2 (TiC form) spectral line of the TC-1 sample was the highest, at 455.2 eV. With the further increase in TiC content (TC-3 sample), the binding energy value of Ti 2p_3/2 (TiC form) starts to decline, and for the TC-10 sample, not only does the binding energy value of the Ti 2p_3/2 (TiC form) spectral line decrease to the lowest compared to TC-1–TC-10, but its strength also significantly decreases. This shows that in TiC, not only does the positive ion energy of the Ti atom begin to decrease, but also the two different forms of Ti atom electrons interact with each other, resulting in a decrease in its own electron state density. In addition, compared with B₄C, the electron offset rate near the Ti atom in TiC is higher than that of the Ti atom in TC4, due to the better conductivity of TiC. However, when the TiC content is low, from a macro point of view, although the electron mobility is better than that of TC4 itself, it is weaker than that of TiC. Therefore, in TiC, the Ti atom’s electron binding ability is also between that of TC4 and TiC. Consequently, when a small amount of TiC is mixed into TC4, the electronegativity of the Ti atom will increase.

The binding energy spectrum lines of Ti 2p_3/2 electrons in TC4 are shown in Figure 8c. Upon the addition of a small quantity of TiC to TC4 (TC-1 sample), the electron binding energy of Ti 2p_3/2 in TC4 increases by 0.2 eV. Additionally, the binding spectral line strength is also the lowest among all samples, indicating that the Ti atom in the TC-1 sample TC4 possesses the highest positive ion energy. Simultaneously, the electron state density of Ti 2p is also the lowest, suggesting a significant electron reverse segregation phenomenon around the Ti atom in TC4 within TC-1. This, along with the findings in Figure 8b, indicates a partial conversion of bound electrons to free electrons around the Ti atoms in the TC-1 sample. As the TiC content is further increased, the binding energy of the Ti 2p_3/2 electrons in the TC-3 sample remains consistent with that of TC-1. Only the spectral line intensity is improved, indicating an increase in the density of 2p electron states around Ti atoms in this sample without a significant change in electron electronegativity. Furthermore, in the TC-5 and TC-10 samples, with further increases in TiC content, the binding energy intensity of Ti 2p_3/2 also increases, along with the density of the 2p electron states around the Ti atoms. It can be concluded that with the increase in TiC content, the positive ion energy of the Ti atom in TC4 decreases, while the state density of the 2p electron increases. Based on the above discussion, it can be concluded that TiC is different from B₄C. The electronegativity of the 2p electrons of Ti atoms in TC4 changes greatly with the increase in TiC content. In contrast, the electronegativity of the 2p electrons of Ti atoms in TC4 not only changes, but also has a significant influence on the electron state density.

Figure 9 shows the XPS spectra of Al and V in different TiC/TC4 samples. Due to the low content of V and the solid solution phase in TC4, the XPS signals are weaker. As shown in Figure 9b, the electron binding energy of Al decreases by 0.2 eV when compared with the results of B₄C doping, which is also caused by the better conductivity of TiC.

Figure 10 shows the C atom binding spectral line in TiC. It is evident that the standard 1s spectral line of the C element in all samples is 285.1 eV. Notably, the C1s electron binding energy spectral line of the C atom in TiC is 281.3 eV, a value that is significantly lower than that in B₄C. Furthermore, when mixed with TC4, the binding energy value of the C atom increases to 281.7 eV. Combined with the Ti 2p electron in Figure 8b, when a small amount of TiC is incorporated into TC4, the positive ion energy of the C element increases. This strengthens the binding ability of electrons. It can be observed that the C1s electron (TiC form) in the BC-3 sample has the largest binding energy value and the highest strength. This indicates that in the BC-3 sample, the C atom has the strongest electron binding ability, the highest electron state density, and a higher probability of electron or ion polarization. With the further increase in TiC content, the conductivity of TiC is improved because the distribution of TiC tends to be uniform, and the electron binding ability of the C atom to C1s is weakened. Further analysis of the C1s spectral line in TiC reveals that as the TiC content increases, the density of the electronic states of C1s decrease. This indicates that incorporating TiC enhances electron mobility around the C atom, which, on the other hand, confirms the weakening of the electron binding ability of the C atom. When considering the conclusion that the density of the Ti 2p electron states increases in Figure 8c, it is evident that there is a migration of 1s electrons from C to Ti atoms in TC4 in TiC [12,13,14,15].

The dielectric constants of various samples are shown in Figure 11. In the 2–10 GHz frequency band, the dielectric constant of TC4 is the lowest, at approximately 5. As shown in Figure 11a, both the real and imaginary parts of the dielectric constant of TiC are the highest, at about 30–40, which is determined by the high electrical conductivity of TiC. As shown in Figure 11c, the overall trend in the real and imaginary parts of the dielectric constant of TiC in the 2–10 GHz frequency band is that the values decrease as the frequency increases.

For the TC4 samples with a low TiC content, the real part of the dielectric constant of TC-1 increases slightly, but it is the lowest among the TC-1-TC-10 samples [16]. The main reason for this is that the electron density of states at Ti 2p_3/2 of TC4 in the TC-1 sample is low. Although Ti 2p_3/2 (in the form of TiC) has a high electron binding energy intensity and a strong electronegativity, its low content generally reduces the electronic polarization ability. Therefore, the real part of the dielectric constant of TC-1 is approximately 6–9. In the high-frequency range of 7–10 GHz, both the real and imaginary parts of the dielectric constant of TC-1 increase with the increase in the external electric field frequency and reach the maximum value at 10 GHz. This indicates that the natural frequency of electrons at the TiC/TC4 interface in the sample is around 10 GHz, and this phenomenon is consistent with the case of adding B4C.

As the TiC content further increases, the real part of the dielectric constant of the TC-3 sample increases significantly to about 12–15. Combining the results of Figure 8b,c, this sample shows a high binding energy and electron spectral line intensity at C1s (in the form of TiC) and Ti 2p_3/2. On the one hand, since the electronegativity of TiC is higher than that of B4C, as the TiC content increases, the electronic polarization ability of TiC at the TiC/TC4 interface is further enhanced. On the other hand, affected by TiC, in TC4, the binding spectral line intensity of the Ti 2p_3/2 of the Ti atoms increases, i.e., the number of electrons around the Ti atoms that can participate in polarization also increases. Furthermore, in the TC-3 sample, the electronic polarization ability of TC4 is enhanced. Therefore, its real part of the dielectric coefficient is the largest. Similar to TC-1, at 7–10 GHz, both the real and imaginary parts of the dielectric constant tend to increase, which indicates that the dielectric loss ability of the BC-3 sample near the resonance frequency is also enhanced, and the electronic polarization ability is enhanced.

After further increasing the TiC content, it can be observed from Figure 8c that the binding energies of the Ti 2p_3/2 spectral lines in TC-5 and TC-10 are lower than those in TC-3 and TC-1, and the binding energy values of the two spectral lines are almost the same. This indicates that the 2p electron density of states around the Ti element in TC-5 and TC-10 tends to be consistent; that is, the electronic polarization abilities are close. It can be concluded from Figure 11a that the two have similar real parts of the dielectric constant. However, for the TC-5 sample, a relatively obvious abnormal dispersion phenomenon occurs near 9.5 GHz, while the abnormal dispersion phenomenon of TC-10 in this frequency band is not obvious [12]. This indicates that the change in the TiC content can also change the natural frequency of the TiC/TC4 interface. In addition, compared with BC-3, the TC-5 sample has a lower frequency (about 8.5 GHz) at which abnormal dispersion occurs in this frequency band and a larger TiC thickness. Similar to B4C, when the TiC content further increases, for the TC-5 and TC-10 samples [17], the electron binding energy of Ti 2p decreases, directly weakening the electronic polarization ability of Ti 2p. The weakening ultimately leads to the dielectric constants of the TC-5 and TC-10 samples being lower than that of TC-3, with values close to 9–10. This indicates that although TiC has a high electronegativity, during the composite process with TC4, the increase in the thickness at the interface can reduce its own electronegativity and thus reduce the polarization ability at the interface.

4. Conclusions

When B4C and TiC are compounded with TC4, although the crystal structure of TC4 is not changed, the internal electronic structure of TC4 can be altered, thereby influencing the polarization form at its interface. The specific conclusions are as follows:

(1)

When the mixing ratio of B4C and TiC to TC4 is 1:30, a strong polarizability exists at the interface, and the real part of the dielectric coefficient reaches the highest value at this time. The dielectric coefficient of pure TC4 powder is 5. After compounding with B4C, the dielectric coefficient increases to 11, and after compounding with TiC, the dielectric coefficient reaches 15. However, further increasing the content of B4C or TiC will lead to a decrease in the dielectric coefficient of TC4.

(2)

After B4C and TiC are compounded with TC4, the binding energy value of the 2p electrons of the Ti element in TC4 is positively correlated with its own polarizability. Namely, the larger the binding energy value of the 2p electrons in the Ti element, the stronger its polarization ability, and the higher the corresponding dielectric coefficient.

(3)

The contents of B4C and TiC can both change the natural frequency of electrons at their interfaces with TC4. At specific contents, an abnormal dispersion phenomenon, i.e., the maximum dielectric loss, will occur at the interface of B4C or TiC with TC4. Due to the different electronegativities of B4C and TiC, when the content ratio of B4C to TC4 is 1:30, the abnormal dispersion frequency is 9.5 GHz; when the mass ratio of TiC to TC4 is 1:20, the abnormal dispersion frequency is 8.5 GHz.