The development and implementation of new technologies are currently considered fundamental prerequisites for creating competitive, multifunctional materials, advancing integrated materials science, and promoting national economic development.

High-temperature, heteromodular, advanced ceramic composite materials are exemplary in this regard. These materials are characterized by superior physical and mechanical properties (such as hardness, strength limits, fracture toughness, and modulus of elasticity), excellent technological properties (such as good machinability with cutting tools), and outstanding operational performance (including wear resistance, resistance to static and dynamic loading, radiation resistance, and more).

The foundation for producing such materials lies in the use of refractory compounds, including: boron carbide, boron nitride, tantalum carbide, zirconium, aluminum, and yttrium oxides, silicon nitride, silicon carbide, titanium and zirconium borides, and carbides of titanium, tungsten, and tantalum. These compounds exhibit high thermodynamic stability, exceptional hardness, and wear resistance—properties they retain even under elevated temperature conditions. This thermal resilience is one of the key factors enabling their effective application in demanding technological environments.

This study focuses on the synthesis and investigation of composite ceramic materials based on boron carbide (B₄C) and silicon carbide (SiC). For the fabrication of the composite, the following initial composition (in wt.%) was selected: B₄C—60%, SiC—20%, TiC—13%, Perlite—3% (appendage).

The selection of these compounds was driven by their unique combination of properties, including high hardness, high melting point, excellent corrosion resistance, wear resistance, and low density.

However, unlike other advanced ceramics, they exhibit low fracture toughness and impact resistance, which limits their broader application despite their advantageous properties. Numerous studies have been devoted to the development of composites based on these compounds for various purposes, particularly in armor applications, due to their low density [1] - [13] .

In addition to boron carbide and silicon carbide, titanium carbide (TiC) was introduced into the composition. This inclusion was based on the known reaction that occurs between titanium carbide and boron carbide during high-temperature processing, resulting in the in-situ formation of titanium diboride (TiB₂), as confirmed by X-ray diffraction analysis ( Figure 1 ). Titanium diboride is also known for its excellent mechanical properties.

The aim of this study was to achieve a highly dispersed and uniform distribution of the newly formed TiB₂ grains within the composite matrix. This uniform distribution is facilitated by an amorphous glassy phase formed by volcanic perlite, which acts as a bonding medium between the grains ( Figure 2 ).

The chemical composition of perlite is as follows (wt.%):

The melting point of perlite is approximately 1240˚C. It contains 76 wt.% glassy phase, with the remainder consisting of crystalline phases and gases trapped during the rapid cooling of erupted lava. Its density ranges from 2.3 to 2.4 g/cm³.

Structural-morphological and elemental composition of the samples was examined using a JEOL JSM-6510LV scanning electron microscope, manufactured in Japan, equipped with an Oxford Instruments X-MaxN energy-dispersive X-ray spectroscopy (EDS) system. Surface imaging was performed using both secondary electrons (SEI) and backscattered electrons (BES) under an accelerating voltage of 20 kV. In certain cases, to reduce surface charging, samples were coated with a ~10 nm Pt layer using a JEOL JEC-3000FC vacuum sputter coater.

The results of the morphological analysis of the polished sample surface are presented in Figure 2 . Gray silicon carbide and white boron carbide grains are clearly distinguishable. Newly formed titanium diboride is also observed between them, the presence of which is confirmed by microspectral and electron imaging data ( Figure 3 , Figure 4 ).

To examine the fracture mechanism of the composite at the microscopic level, a freshly fractured sample was prepared, and its fracture surface was analyzed using a scanning electron microscope (SEM). SEM image of the fracture surface is presented in Figure 5 .

Figure 5 illustrates that the morphological features are consistent and uniform throughout both the surface and the volume of the sample. The fracture mechanism is characterized by a combination of transcrystalline and ductile modes. Furthermore, the crystals exhibit stepwise fracture, which effectively impedes crack propagation. This behavior is corroborated by the mechanical strength data presented in Table 1 .

As observed in Figure 4 , titanium diboride forms a shell around the silicon carbide grains. In the event of crack initiation within a carbide grain, it localises the crack and reduces its propagation rate [1] . Additionally, unreacted boron carbide and titanium diboride grains are interconnected by thin amorphous glassy bridges [2] . The composite was fabricated using the hot-pressing method at 1620˚C. The physical and technical properties of the composite are presented in Table 1 .

As shown in Table 1 , the obtained composite is characterized by high physical and mechanical properties and low volume porosity, which enhances its application potential. To further characterize the composite, Z. Kovziridze’s formulas describing the dependence of mechanical properties on the porous phase and the correlation between the morphology of the crystalline phase and macromechanical characteristics were applied [14] . For this purpose, the morphology of pores and crystals was examined using microstructural images. The data presented in Table 2 and Table 3 were utilized as input for the corresponding formulas.

${\sigma }_{m/p}=P/F_p\cdot P_d\cdot P_{vol}\cdot P_m$

where:

P—applied load in bending mechanics (MPa);

F_p—pore shape factor;

P_d—pore distribution factor in the matrix;

P_vol—volume fraction of the porous phase in the matrix;

P_m—average pore size.

${\sigma }_{m/p}=P/F_p\cdot P_d\cdot P_{vol}\cdot P_m=389/2\times 0.9\times 0.83\times 7=389/10.46=37.2\text{MPa}.$

${\sigma }_d=P{F}_{kd}/K_m{K}_v{F}_{kf}$

where:

P—applied load in bending or compression mechanics (MPa);

F_kd—crystal distribution factor in the matrix;

K_m—average crystal size (µm);

K_v—volume fraction of crystals in the matrix (wt.%);

F_kf—crystal shape factor.

${\sigma }_d=P\times F_{kd}/K_m{K}_v{F}_{kf}=389\times 0.9/6\times 89.17\times 4.5=389\times 0.9/2407.6=0.17$

${\sigma }_d=P\times F_{kd}/K_m{K}_v{F}_{kf}=1923\times 0.9/6\times 89.17\times 4.5=1730.7/2407.6=0.72$

The formula accounts for both volumetric and surface defects of crystals, as well as the micro- and macrostructural volumetric and surface morphology of the crystalline phase, its distribution within the matrix, and the transformations occurring due to chemical and physicochemical processes during material consolidation. These properties are determined experimentally.

Notably, the proposed formula is applicable to a wide range of ceramic materials and ceramic composites, including metal-ceramics, bio ceramics, glass-ceramics, and glass-metal-ceramics. It captures the relationship between the macro mechanical properties of these materials, specifically, their ultimate failure characteristics, and key morphological parameters of the crystalline phase, such as crystal size, shape, distribution, and volume fraction within the matrix, as well as the crystal shape factor. In addition, the formula accounts for the contribution of the most mechanically robust phase in the consolidated material, reflecting its critical role in determining the overall performance characteristics essential for industrial application and long-term service reliability.

During thermal treatment, key factors influencing the final properties of ceramic materials include the dynamics of crystal formation, their spatial distribution within the matrix, and the evolution of crystal morphology. These aspects, thoroughly examined in this study, are closely linked to the physicochemical processes that occur under thermal stress. The proposed formula offers a comprehensive framework for modeling the correlation between the morphology of the crystalline phase and the macro mechanical properties of ceramic components. Its applicability extends to all types of ceramics and ceramic composites employed in advanced technologies, diverse engineering sectors, and everyday applications.

The B₄C-TiC-SiC-TiB₂-perlite composite, which demonstrates high mechanical and operational properties, was fabricated via hot pressing at a temperature of 1620˚C. However, as the results indicate, the correlation is not strong. This may be attributed to the high crystal shape factor. Notably, attrition milling and planetary ball milling of the mixture were deliberately avoided, maintaining the materials’ original dispersion. The disparity between the smallest and largest particles was substantial, which significantly contributed to the reduction in correlation. Consequently, the correlation coefficient was found to be 0.17 for bending and 0.72 for compression.

Ideally, the crystal shape factor should not exceed 3, and the crystal size should preferably remain within the range of 7 - 8 microns, while also being uniformly distributed throughout the matrix. Experimental evidence shows that fine-grained samples exhibit higher strength compared to coarse-grained ones [15] - [19] , since the length of Griffith microcracks is determined by grain size. This phenomenon is presumably related to stress accumulation at grain boundaries caused by anisotropic thermal expansion [20] - [28] .

The volume and surface electrical resistivity (ρ_v and ρ_s) of the obtained material was experimentally determined as a function of temperature in the range of 25˚C - 300˚C. Measurements were conducted using a specially designed thermally controlled cell, simultaneously on two samples, with an electronic ohmmeter employed for resistance measurements. The test samples were disk-shaped, with a diameter-to-height ratio of approximately D/H ≈ 5. Air-dried samples (25˚C, relative humidity 47.5%) were placed in the measurement cell, and their volume (R_v) and surface (R_s) resistance values (Ω) were recorded. Subsequent measurements in the temperature range of 100˚C - 300˚C were performed at 50˚C intervals. Using the corresponding calculations, specific resistivity values ρ_v (Ω∙m) and ρ_s (Ω) were obtained. The resulting “ρ_v,s − t” relationships are presented in Figure 6 .

It was established that the variation of volume resistivity (ρ_v) with temperature is linear, and within the 25˚C - 300˚C interval, a nearly twofold decrease in specific resistivity is observed. A noteworthy behavior is exhibited by the surface resistivity (ρ_s), whose values were determined under conditions of reversible temperature cycling in the range of 25˚C - 300˚C. For the initial sample (Curve 2), the ρ_s values were relatively high at room temperature, showed a sharp decline in the range of 25˚C - 150˚C, and subsequently aligned with the ρ_v values. During the cooling phase (Curve 2'), ρ_s values closely matched those of ρ_v, with only a minor deviation (≈1 Ω).

The distinct behavior of the “ρ_s − t” curve under temperature reversal is likely attributable to condensed moisture on the surface of the initial sample, which evaporated during heating, leading to the convergence of ρ_s and ρ_v values at higher temperatures.

The key electrical properties of the investigated material, calculated across the temperature range of 25˚C - 300˚C, are presented in Table 4 .

The resulting material, primarily composed of titanium, silicon, and boron carbides, well-known for their electrical properties, exhibits electrical behavior characteristic of semiconductor materials.

During the hot pressing at 1620˚C, a reaction occurred between titanium carbide and boron carbide, resulting in the formation of titanium diboride. This reaction contributed to a significant enhancement of the composite’s mechanical properties. Additionally, the presence of perlite in the composite led to the formation of a glassy phase that creates so-called “bridges” with the carbide grains, further improving the mechanical performance of the material. A clear correlation was established between the matrix composition and the mechanical properties of the material, specifically showing the dependence of mechanical characteristics on the content of the porous phase.

The resulting composite in the B₄C-SiC-TiC-TiB₂ system, doped with 3 wt.% glassy perlite, primarily composed of titanium, silicon, and boron carbides known for their electrical properties, exhibits electrical behavior characteristic of semiconductor materials.