Search Results (23)

The chemical and microstructural transformation of the surface of a 31.5 vol.% ZrB₂-31.5 vol.% HfB₂-27 vol.% SiC-10 vol.% C_CNT ultrahigh-temperature ceramic sample (where C_CNT refers to carbon nanotubes) was studied under the influence of a subsonic N₂-plasma flow with the addition of 5 mol% methane, simulating aerodynamic heating in the atmosphere of Titan. As in the case of pure nitrogen flow, it was found that silicon carbide is removed from the surface. Zirconium and hafnium diborides are partially transformed into a Zr-Hf-B-C-N solid solution in the experiment conducted. XRD, Raman spectroscopy, and SEM-EDX analysis show that the presence of C₂ in the N₂-CH₄ plasma flow leads to surface carbonization (formation of a graphite- and diamond-like coating with a high proportion of amorphous carbon), resulting in significant changes in the microstructure and emissivity, potentially affecting the catalytic properties of the surface. Full article

This study examined the physical, mechanical, tribological, and corrosion properties of copper metal matrix composites reinforced with zirconium diboride (ZrB₂). Cu-xZrB₂ composites (x = 0.5, 10, 15, 20 wt.%) were produced by the ball-milling process and spark plasma sintering (SPS). Introducing ZrB₂ particles into copper matrix composites significantly improves their mechanical and tribological properties while deteriorating their density, porosity, and corrosion properties. It was shown that the relative densities of the composites gradually decreased from 96% to 90%, with an increase in the ZrB₂ content to 20 wt.%. Likewise, hardness, compressive strength, and wear resistance improved with increasing ZrB₂ content in the copper matrix. Corrosion resistance tests in a 0.05 M sulfuric acid environment showed a disproportionate decrease in the resistance of this composite with an increase in the concentration of the ceramic phase compared to other environments. Full article

This study aimed to investigate the physical, mechanical, corrosion, and tribological properties of Cu-based composites with varying zirconium diboride content. The composites were successfully consolidated using spark plasma sintering (SPS) at temperatures of 850 °C and 950 °C and a pressure of 35 MPa. The effect of the ZrB₂ content and the sintering temperature on the properties of the Cu-based composites was investigated. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction were used to analyse microstructure evolution in copper matrix composites. Microhardness tests were used to evaluate mechanical properties. Wear behaviour was evaluated using a ball-on-disc method. Corrosion properties were estimated on electrochemical tests, such as potentiodynamic polarisation. The results demonstrated an enhancement in the density and porosity of the composites as the sintering temperature increased. A uniform dispersion of ZrB₂ was observed in the copper matrix for all composites. With an increase in the content of the ZrB₂ reinforcement phase, there was an increase in microhardness and an improvement in the wear resistance of the sintered composites. A reduction in densification and corrosion resistance of Cu-based composites was observed with increasing ZrB₂ content. Full article

Copper matrix composites with zirconium diboride (ZrB₂) were synthesised by ball milling and consolidated by Spark Plasma Sintering (SPS). Characterisations of the ball-milled composite powders were performed by scanning electron microscopy (SEM), X-ray diffraction, and measurement of the particle size distribution. The effect of the sintering temperature (1123 K, 1173 K, and 1223 K) and pressure (20 MPa and 35 MPa) on the density, porosity, and Young’s modulus was investigated. The relationship between the change of Orb content and physical, mechanical, and electrical properties was studied. Experimental data showed that the properties of Cu–Orb composites depended significantly on the SPS sintering conditions. The optimal sintering temperature was 1223 K with a pressure of 35 MPa. Composites exhibited a high degree of consolidation. For these materials, the apparent density was in the range of 93–97%. The results showed that the higher content of Orb in the copper matrix was responsible for the improvement in Young’s modulus and hardness with the reduction of the conductivity of sintered composites. The results showed that Young’s modulus and the hardness of the Cu 20% Orb composites were the highest, and were 165 GPa and 174 HV0.3, respectively. These composites had the lowest relative electrical conductivity of 17%. Full article

The process of Thermal spray is effective for creating a metal matrix composite (MMC) by embedding zirconium diboride reinforcement into a molybdenum matrix. Both materials Mo and ZrB₂ have different characteristics, but they have good thermal shock resistance, maintain strength at elevated temperatures, and stability in extreme environments. The study focused on creating MoZrB₂ composites using a thermal spray coating technique, varying the parameters of spraying distance, number of passes, and gas pressure, and testing the resulting castings to evaluate their hardness and Young’s Modulus. The primary objective of the research was to use the Taguchi technique for identifying the optimal parameters for generating the highest Young’s Modulus and hardness for the castings. The Taguchi method integrates experimental and analytical principles to identify the most significant parameter affecting the response, which can significantly enhance overall performance. The study found that the optimal parameters were a spraying distance of 20 cm, gas pressure of 6 bar, and the number of passes of 18. The Taguchi method accurately predicted the parameters that produced the highest properties for the composite coatings, which demonstrated good surface formation without hot cracks and fewer pores, with well-formed metallurgical bonding between the coating and the substrate. Full article

Steering gearbox bodies, which are produced from spheroidal graphite cast iron, experience wear and gaps over time since they operate under load. It is important to strengthen steering gearbox bodies to avoid this. In this study, a steering gearbox body was produced from a spheroidal graphite cast iron material with zirconium diboride at varying rates (0%, 0.227%, 0.455%, and 1.364%). Samples of the material were prepared according to established standards for hardness, compressive strength, and wear resistance tests. The mechanical properties of test samples with and without zirconium diboride (hardness, compressive strength, and wear resistance) were compared. Sample C showed the highest hardness measurement of 243 HB after adding 0.455% zirconium diboride. As the rate of addition increased, the values obtained from the hardness measurement test also increased. Sample C had the highest compressive value of 1438 MPa, with a 0.455% addition rate. It was found that the compressive strength values also increased as the addition rate increased. Wear tests were conducted to analyse wear volume, wear rate, and friction coefficients. A scanning electron microscope (SEM) device was utilised to identify wear mechanisms on the worn surfaces of the samples. Per the results of this study, wear volume values were found to increase with the load value. Full article

The effect of zirconium diboride (ZrB₂) and titanium diboride (TiB₂) on the microstructure as well as the physical, mechanical, and tribological properties of composites based on 316 L steel is presented. Each reinforcing phase was added to the base alloy in the amount of 5 wt% and 10 wt%. The composites were fabricated by the SPS process (Spark Plasma Sintering). The results show that the weight fraction of the reinforcing phase affects the physical, mechanical, and tribological properties of the sintered composites. The sintered materials were characterized by a very high level of density. The addition of TiB₂ has proved to be effective in increasing the hardness and compressive strength of the composites. The hardness of the composites with the addition of 10% TiB₂ increased by 100% compared to the hardness of sintered 316L steel. It was found that introducing ZrB₂ to the steel matrix significantly improved the wear resistance of the composites. The results showed that compared to 316L steel with the wear rate of 519 × 10⁻⁶ mm³/Nm, the wear rate of the composites containing 10% ZrB₂ decreased more than twice, i.e., to 243 × 10⁻⁶ mm³/Nm. Full article

Thermal spray is an effective process for the fabrication of a metal matrix composite (MMC), where a zirconium diboride reinforcement is embedded in a molybdenum matrix to enable the combining of favorable properties in a new composite. The combination of two leading materials in the category of ultra-high-temperature ceramics (UHTCs) is due to a very high melting point (Mo: 2623 °C and ZrB₂: 3245 °C), high thermal conductivity (Mo: 139 W/m°C and ZrB2: 24 W/m°C), good thermal shock resistance, low coefficient of thermal expansion (Mo: 5.35 µm/m°C and ZrB₂: 5.9 × 10⁻⁶ K⁻¹), retention of strength at elevated temperatures and stability in extreme environments. Thermal spraying of the Mo/ZrB2 composite possesses a non-linear behavior that is influenced by many coating variables. This characteristic makes finding the optimal factor combination difficult. Therefore, an effective and strategic statistical approach incorporating systematic experimental data is needed to optimize the process. In this study, the L9 orthogonal array in the Taguchi approach was utilized to optimize the spraying distance (SD), number of passes (NP), pressure (P) and coat-face temperature (T_CF) using a dummy fiberglass substrate. The performance was evaluated based on the coating density (C_d) of the surfaces. Based on confirmation tests, our Taguchi analysis determined the ideal process parameters, which considerably enhanced the coating process. From the output response of the ANOVA, the most influential parameters for achieving a high coating density (C_d) were determined to be SD = 20 cm, NP = 24, P = 4 bar and T_CF = 330 °C ((SD.)1-(NP.)3-P2-(S.T.)3). These observations show that the coating density (C_d) was significantly influenced by the coat-face temperature, followed by the number of passes, spraying distance and pressure with the following contributions 6.29, 17.89, 17.42 and 3.35%, respectively. Full article

In order to reduce the sintering temperature and improve the mechanical properties of B₄C ceramics, ZrB₂ was formed in situ using the SPS sintering method with ZrO₂ and B₄C as raw materials. Thermodynamic calculations revealed that CO pressure affected the formation of ZrB₂ at temperatures from 814 °C to 1100 °C. The experimental results showed that the ZrB₂ grain size was <5 µm and that the grains were uniformly distributed within the B₄C ceramics. With an increase in ZrO₂ content, the Vickers hardness and flexural strength of the B₄C ceramics first increased and then decreased, while the fracture toughness continuously increased. When the content of ZrO₂ was 15 wt%, the Vickers hardness, fracture toughness and flexural strength of B₄C ceramics were 35.5 ± 0.63 GPa, 3.6 ± 0.24 MPa·m^1/2 and 403 ± 10 MPa, respectively. These results suggest that ZrB₂ inhibits B₄C grain growth, eliminates crack tip stress, and provides fine grain to strengthen and toughen B₄C ceramics. Full article

Laser additive manufacturing is an advanced material preparation technology, which has been widely used to prepare various materials, such as polymers, metals, ceramics and composites. Zirconium diboride (ZrB₂) reinforced copper composite material was fabricated using laser direct energy deposition technology. The microstructure and phase composition of the composite material were analyzed, and the influence of laser energy density on the microstructure and mechanical properties of composite materials was discussed. The results showed that the needle-like ZrB₂ ceramic reinforcement was successfully synthesized via an in-situ synthesis reaction. The composites were mainly composed of needle-like ZrB₂, Ni dendrites and a Cu matrix. The morphological changes of Ni dendrites could be observed at the interface inside the composite material: cellular crystals → large-sized columnar dendrites → small-sized dendrites (along the solidification direction). The continuous Ni dendritic network connected the ZrB₂ reinforcements together, which significantly improved the mechanical properties of the composite material. At a laser energy density of 0.20 kJ/mm², the average microhardness of the composite material reached 294 HV_0.2 and the highest tensile strength was 535 MPa. With the laser energy density increased to 0.27 kJ/mm², the hardness and tensile strength decreased and the elongation of the Cu composites increased due to an increase in the size of the ZrB₂ and a decrease in the continuity of the Ni dendritic. Full article

Oxide impurities such as boria (B₂O₃) and zirconia (ZrO₂) on the surfaces of zirconium diboride (ZrB₂) particles are known to limit their sinterability. Among the impurities, B₂O₃ on the surface of ZrB₂ particles could be easily removed by methanol or hydrofluoric acid. However, the remaining ZrO₂ still gave negative influences on the sinterability. In this study, ZrB₂ particles were treated with various acids to remove oxide impurities on their surfaces. The acid treatments were found to vary in efficacy, according to acid type, and affect the crystallinity and morphology of ZrB₂ particles to varying degrees, in some cases forming additional impurities. In particular, the change in the oxygen content of the ZrB₂ particles induced by acid treatment was found to depend on the type of acid. The results of the acid treatments were compared which revealed that HNO₃ treatment optimizes the purity of ZrB₂ particles. In addition, the effects of acid treatment on the surface properties of ZrB₂ particles were considered. In particular, the correlation between the surface properties of the acid-treated ZrB₂ particles and their dispersibility in aqueous solution was investigated. Full article

To enhance the properties of tungsten diboride, we have synthesized and characterized solid solutions of this material with chromium, molybdenum, rhenium and zirconium. The obtained materials were subsequently deposited as coatings. Various concentrations of these transition metal elements, ranging from 0.0 to 24.0 at.%, on a metals basis, were made. Spark plasma sintering was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of both samples (sintered compacts and coatings) were examined using energy dispersive X-ray spectroscopy and X-ray diffraction. Microindentation was utilized to measure the Vickers hardness. X-ray diffraction results indicate that the solubility limit is below 8 at.% for Mo, Re and Zr and below 16 at.% for Cr. Above this limit both diborides (W,TM)B₂ are created. Addition of transition metals caused decrease of density and increase of hardness and electrical conductivity of sintered compacts. Deposited coatings W_1−xTM_xB_y (TM = Cr, Mo, Re, Zr; x = 0.2; y = 1.7–2) are homogenous, smooth and hard. The maximal hardness was measured for W-Cr-B films and under the load of 10 g was 50.4 ± 4.7 GPa. Deposited films possess relatively high fracture toughness and for WB₂ coatings alloyed with zirconium it is K_1c = 2.11 MPa m^1/2. Full article

The aim of this study was to carry out the consolidation of zirconium diboride-reinforced composites using the SPS technique. The effect of the adopted method of powder mixture preparation (mixing in Turbula or milling in a planetary mill) and of the reinforcing phase content and sintering temperature on the microstructure, physical properties, strength and tribological properties of sintered composites was investigated. Experimental data showed that the maximum relative density of 94%–98% was obtained for the composites sintered at 1100 °C. Milling in a planetary mill was found to contribute to the homogeneous dispersion and reduced clustering of ZrB₂ particles in the steel matrix, improving in this way the properties of sintered steel + ZrB₂ composites. Morphological and microstructural changes caused by the milling process in a planetary mill increase the value of Young’s modulus and improve the hardness, strength and wear resistance of steel + ZrB₂ composites. Higher content of ZrB₂ in the steel matrix is also responsible for the improvement in Young’s modulus, hardness and abrasive wear resistance. Full article

Our goal is to develop a structural ceramic for high-temperature applications in which silicon carbide-based materials (SiCs) are used as matrix composites. The potential of SiCs to deposit a mixture of SiC and zirconium diboride (ZrB₂) plasma spray coating is analyzed. To deposit thermal barrier layers containing up to 50 vol.% SiC, a high-pressure plasma spray (HPPS) process was used. Although the SiC cannot be deposited by thermal spray, a mixture of SiC and zirconium diboride (ZrB₂) was deposited because these two compounds form a eutectic phase at a temperature below SiC decomposition. The preference was two different forms, 3 mm and 1 mm, of graphite substrates with different thickness values. A comparison of the morphology of SiC-ZrB₂ coatings before and after thermal treatment was performed by applying heat to the surface of a gas torch and traditional furnace between 800 °C and 1200 °C. The growth of the oxide scale was calculated with X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), and density. The oxide scale consists of a SiO₂ layer with ZrO₂ groups. The findings indicate a greater potential for the studied material in protecting against high-temperature oxidation and in a wide variety of aerospace applications. Full article

The effects of different reinforcement shapes on stability and repeatability of micro electrical discharge machining were experimentally investigated for ultra-high-temperature ceramics based on zirconium diboride (ZrB₂) doped by SiC. Two reinforcement shapes, namely SiC short fibers and SiC whiskers were selected in accordance with their potential effects on mechanical properties and oxidation performance. Specific sets of process parameters were defined minimizing the short circuits in order to identify the best combination for different pulse types. The obtained results were then correlated with the energy per single discharge and the discharges occurred for all the combinations of material and pulse type. The pulse characterization was performed by recording pulses data by means of an oscilloscope, while the surface characteristics were defined by a 3D reconstruction. The results indicated how reinforcement shapes affect the energy efficiency of the process and change the surface aspect. Full article