ZrB2 Composites Research Articles

Microstructure evolution of diboride and carbide phases in platelets-toughened (Zr, Ti)C-(Ti, Zr)B2 ceramics via reaction pressureless sintering

Fully dense (Zr, Ti)C-(Ti, Zr)B2 composites were sintered via reactive pressureless sintering of ZrB2 and TiC based on the in-situ reaction and solid solution coupling effects. The effects of TiC content and sintering temperature on microstructure evolution and mechanical properties were explored. Elongated (Ti, Zr)B2 platelets were observed, stemming from the in-situ reaction between ZrB2 and TiC, and exhibited a high aspect ratio with the increase of TiC content. Besides, phase decomposition structures featuring semi-coherent interfaces were identified in the ZrB2-70mol.% TiC system sintered at 2200 °C, attributed to the chemical miscibility gap. High values of hardness (27.0 GPa), flexural strength (533 MPa), and fracture toughness (4.6 MPa m1/2) are found in ZrB2-70 mol.% TiC composite sintered at 2200 °C. The low porosity, solid solution strengthening, grain refinement caused by carbide phase decomposition, and high dislocation densities and strain concentration at the semi-coherent interfaces of carbide phase decomposed structures play an important role on hardening and strengthening. Furthermore, the presence of in-situ synthesized (Ti, Zr)B2 platelets with a high aspect ratio significantly contributes to toughening.

Microstructure and mechanical properties of Cu–Cr–Zr–ZrB2 composites by novel fabrication process of ultrasonic vibration treatment

Copper matrix composites with dual-scale particles were fabricated through casting with reaction. Ultrasonic vibration has been successfully introduced into the melt at about 1523 K while the microstructural development and mechanism of copper matrix composites with high-performance through a novel method of casting with ultrasonic vibration treatment are investigated. When ultrasonic vibration is applied, the distribution of micro-scale particles is greatly improved. Primary Cr phase convents to non-dendrite and large aggregates of ZrB2 particles are disrupted into small clusters because of acoustic cavitation and acoustic streaming. The ultimate tensile strength and elongation of Cu-1wt%Cr-0.3 wt%Zr-1wt%ZrB2 composite in as-cast state were 321 MPa and 14.37 %, recording a 28.4 % and 14 % increment respectively compared with the sample without treatment. After solution treatment, deformation and aging subsequently, the uniform distribution of reinforcements also decreases the average transverse grain thickness and increases the dislocation density which improve the comprehensive properties.

Densification mechanism, microstructure, and thermionic emission property at the low temperature of spark plasma sintered (LaBa)B6–ZrB2 composite

The development of a high-power and long-life thermionic ceramic cathode poses significant challenges, namely the need for high electron emission capacity at low temperature and excellent machinability. In this paper, the first-principles method was used to obtain the (La0.5Ba0.5)B6 with the lowest work function, and (La0.5Ba0.5)B6–ZrB2 composite with high relative density of 98.08 % was prepared by spark plasma sintering (SPS) at T = 1800 °C, under which the densification mechanism transformed from the particle rearrangement into the grain boundary diffusion, and the corresponding apparent activation energies were 282.75 kJ/mol and 466.54 kJ/mol, respectively. The maximum current density of 12.93 A/cm2 at T = 1500 °C of the composite was higher than that of 11.71A/cm2 at T = 1600 °C of LaB6, which can be attributed to the high Fermi level and weak electronic constraints of (La0.5Ba0.5)B6. The practical work function distribution (PWFD) of 0.36 eV indicated the composite had excellent emission uniformity.

Investigation on Mechanical Behavior of LM26 Aluminum Alloy—ZrB2 and Copper-Coated Short Steel Fiber-Reinforced Composites Using Stir Casting Process

Investigation on Mechanical Behavior of LM26 Aluminum Alloy—ZrB2 and Copper-Coated Short Steel Fiber-Reinforced Composites Using Stir Casting Process

Ultrafast high-temperature sintering (UHS) of WC and WC-containing ZrB2

WC and ZrB2 are refractory ceramics with excellent thermophysical properties and melting temperatures exceeding 2800°C. Both materials require the application of external pressure and long sintering times for their consolidation. In particular, commercially available ZrB2 powders are intrinsically difficult to sinter and usually need long pre-processing steps such as high-energy ball milling. Ultrafast high-temperature sintering (UHS) is a recently developed technique that enables the consolidation of bulk ceramics within minutes. In the present work, pure WC was efficiently densified to above 98% in just 3 min by UHS. Moreover, small WC additions enhanced ZrB2 densification by activating liquid phase sintering. Samples containing 5 and 10 vol% WC were sintered to 95 and 96%, respectively, in 2 min. All the WC initially present in the blend reacts to form a liquid phase during sintering and solidifies as WB and (Zr,W)C upon cooling. The formation of a ZrB2-(Zr,W)B2 core-shell structure was detected in all the sintered composites. The hardness of UHS samples reaches 15 GPa (WC - ZrB2 composites) and 21 GPa (pure WC), similar to that measured in materials obtained by slower and more sophisticated pressure-assisted sintering techniques.

Effect of TaC and graphene nanoplatelets on the microstructure and mechanical properties of ZrB2

In this experiment, in order to investigate the effect of TaC addition on the microstructure, densification and mechanical properties of ZrB2 composites reinforced with graphene nanoplatelets (GNP), three composites were fabricated via spark plasma sintering (SPS) at 1900 °C. Relative density was determined by Archimedes method. The XRD and EDS analyses were used to explore the phase composition and elemental distribution. Also, Field emission scanning electron microscopy (FE-SEM) was employed to characterize the microstructure (grain size and porosity). Flexural strength, fracture toughness and hardness were determined by three-point bending test, single-edge notched beam (SENB) and macro and micro Vickers methods, respectively. The results showed that the presence of the GNP, alone and combined with TaC, increases the relative density sharply to 99.6 %. In addition, full densification occurred by the addition of 10 and 20 vol% TaC compared to the monolithic ZrB2 ceramic with 83 % relative density. Maximum flexural strength and fracture toughness of 580 MPa and 4.5 MPa.m0.5 were obtained, respectively, for ZrB2- GNP and ZrB2- GNP doped with 10 vol% TaC.

Oxidation resistance up to 2600 K under air plasma of (Zr/Hf)B2 composites containing 20 vol% AlN for hypersonic applications

Fully-dense ZrB2 and HfB2 composites were elaborated by Spark Plasma Sintering with 20 vol% AlN to replace SiC or TaSi2 with the objective to improve the oxidation resistance at very high temperature. This study follows the ones on (Zr/Hf)B2-SiC and (Zr/Hf)B2-TaSi2 systems carried out in the same conditions (Pellegrini et al. 2022a; Pellegrini et al. 2022b). Oxidation behavior of several samples in air plasma conditions, at 1000 Pa total pressure and from 1980 K up to 2600 K, was studied using the MESOX facility implemented at the focus of a solar furnace. The mass variation of the samples during oxidation duration of 300 s on a temperature plateau was measured. The characterization of the oxidized samples was done using SEM, EDS, XRD, XPS and Raman. A better oxidation resistance was obtained with these new compositions as, for example, no mass loss up to 2600 K was measured for the ZrB2-20 vol% AlN composite due to the protective effect of the aluminum-rich phase formed by oxidation and confirmed by the cross-section analysis.

Effect of zirconium diboride addition in zirconium dioxide reinforced aluminum-based composite fabricated by microwave sintering technique

In the present investigation, zirconium dioxide (ZrO2) and zirconium diboride (ZrB2) have been used in the development of an aluminum-based composite. A microwave sintering technique was employed for the processing of the composite. The aluminum-based composite was developed with the constant 5 wt.% of ZrO2. The weight percent of ZrB2 increased from 2.5% to 7.5%. Uniform distribution of the reinforcement particles was observed for the composition Al–5 wt.% ZrO2–2.5 wt.% ZrB2 composite and Al–5 wt.% ZrO2–5 wt.% ZrB2 composite. The relative density of Al–5 wt.% ZrO2–5 wt.% ZrB2 composite was found to be 0.9874. The percent porosity of the Al–5 wt.% ZrO2–5 wt.% ZrB2 was 1.259%. Results showed that hardness, compressive strength, % tensile strength, and fatigue strength (at 1 × 107 cycles) were improved by about 74.28%, 18.18%, 58.77%, and 60.77%, respectively. XRD of the Al/ZrO2/ZrB2 composite showed the presence of Al, ZrO2, ZrB2, MgAl2O4, and Al2Cu phases. The number of grains per square inch for composition Al–5 wt.% ZrO2–5 wt.% ZrB2 composite was found to be 989.11. This result showed that a finer grain structure has been obtained after the solidification of Al–5 wt.% ZrO2–5 wt.% ZrB2 composite. The fracture surface of the Al–5 wt.% ZrO2–5 wt.% ZrB2 composite was composed of a dendrite structure with micro-porosities. Dimples were also not observed from the tensile fracture surface morphology of the composite.

Preparation, mechanical properties and long-term ablation resistance of Cf/SiBCN–ZrB2 composites

The Cf/SiBCN–ZrB2 composites were prepared by dipping and winding combined with reactive hot pressing. The flexural strength and fracture toughness reached 261 MPa and 11.96 MPa • m1/2, respectively, through continuous carbon fibers debonding, pulling and bridging mechanisms. Excellent mechanical properties ensured that the Cf/SiBCN–ZrB2 composites remained intact after exposure to a plasma flame with a heat flux of 9.37 MW/m2 for 300 s, with the mass and linear ablation rates of 1.78 mg/s, 1.01 μm/s, respectively. The excellent ablation resistance was due to the formation of dense oxide layers separating the matrix from the plasma flame. The SiO2 formed in the low-temperature areas away from the center was the main ablation-resistant barrier, while the ZrO2/SiO2 double oxide layer formed in the high-temperature region at the center was the major ablation-resistant barrier.

Scratch, fretting, and sliding wear of a ZrB2–hardened Zr3Al2 intermetallic–ceramic composite

The unlubricated wear behaviour of a very recently developed ZrB2–hardened Zr3Al2 intermetallic–ceramic composite was investigated for the first time. In particular, tribological tests of scratch, fretting, and sliding were performed with no external lubrication under varied loads against diamond counterparts to thus account for different types and conditions of frictional contacts, and the worn surfaces were characterised in detail to identify the corresponding wear modes and mechanisms. It was found that under scratch wear the Zr3Al2–ZrB2 composite undergoes a ductile-to-brittle transition with increasing applied load, with an increasing plastic damage from low loads and eventually also with macro-chipping at intermediate loads and massive meso-/macro-chipping at high loads. It was also found that the Zr3Al2–ZrB2 composite is resistant to both fretting wear and sliding wear, exhibiting low specific wear rates. Thus, under fretting wear it underwent mild damage first by fretting fatigue in the form of slight surface abrasion and then by fretting oxidation with formation of a self-lubricating oxide tribolayer. The severities of the fretting fatigue and fretting oxidation increased with increasing applied load, with the former dominating over the latter for low and intermediate loads and the opposite being the case for high loads. Similarly, under sliding wear it also underwent only mild damage, now first by mechanical sliding wear and then by oxidative sliding wear, both of increasing severity with increasing applied load, but with the abrasion dominating over the oxidation. Given the promising wear behaviour observed in this first tribological study against diamond, it is proposed that these Zr3Al2–ZrB2 composites merit further investigation under an ample set of possible engineeringly-relevant wear conditions.

Spark plasma sintering of polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composites

AbstractThis paper has studied the densification, microstructure, and properties of polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composites prepared by spark plasma sintering (SPS). The highest relative density of 98.7% is obtained at the SPS condition of axial mechanical pressure 50 MPa, sintering temperature 1900°C and holding time 5 min. The Vickers hardness decreases linearly from the maximum value of 21.49 GPa to the value of 8.24 GPa with the tested temperature increased from room temperature to 1000°C. The effects of crack deflection and bridging have resulted in the fracture toughness of 4.56 MPa m1/2 of dense polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composite. The J1kV of 7.02 A/cm2 obtained at 1600°C, the work function of 2.743 eV determined by ultraviolet photoelectron spectroscopy, and the good oxidation resistance below 1100°C in air have revealed that the dense polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composite has a good potential to be a promising hot cathode material.

Numerical analysis of microchannel heat sink composed of SiC and CNT reinforced ZrB2 composites

As a result of the development of micro-electro-mechanical systems (MEMS), it is now feasible to achieve enormous heat transfer, even though electrical and electronic devices have more compact spaces. A heat sink is a device that collects significant amounts of heat from various electrical and electronic surfaces and then releases that heat into the surrounding environment. In the current study, a ceramic microchannel heat sink (MCHS) with a rectangular channel having a length of 10 mm and dimensions of 57×180 μm was investigated numerically. Because ceramics are valuable materials that can withstand corrosive environments and extreme temperatures, they are statistically analyzed to evaluate whether a substance can work under such harsh conditions. Firstly, the finite element approach was used to solve the governing equations of the solid domain as ZrB2 composites and the fluid domain as water. Subsequently, a numerical analysis was conducted on an MCHS constructed from ZrB2 composites reinforced with SiC and CNT in a variable proportion of 20 vol.% and 10 vol.%, respectively. The results reveal the most significant temperature reduction for an ultra-high heat flux for the ZrB2 composite reinforced with 20 vol.% SiC, followed by the ZrB2 composite reinforced with 20 vol.% SiC & 10 vol.% CNT at Reynolds number 250. The fundamental causes of the exceptional heat transfer rate are the high surface density of the microchannel and the excellent thermal conductivity of the UHTCs.

Investigation of the density and microstructure homogeneity of square-shaped B4C-ZrB2 composites produced by spark plasma sintering method

Square-shaped monolithic B4C and B4C-ZrB2 composites were produced by spark plasma sintering (SPS) method to investigate the effect of 5, 10, 15 vol% ZrB2 addition on the densification, mechanical and microstructural properties of boron carbide. The relative density of B4C increased with the increasing volume fraction of ZrB2 and density differences in different regions of the sample narrowed down. Homogeneous density distribution and microstructure were accomplished with the increasing holding time from 7 to 20 min for the B4C-15 vol% ZrB2 composites, and the highest overall relative density was achieved as 99.23%. The hardness and fracture toughness of composites were enhanced with the addition of ZrB2 compared to monolithic B4C. The enhancement in fracture toughness was observed due to the crack deflection, crack bridging and crack branching mechanisms. The B4C-15 vol% ZrB2 composite exhibited the combination of superior properties (hardness of 33.08 GPa, Vickers indentation fracture toughness of 3.82 MPa.m1/2).

Online acoustic emission measurement of tensile strength and wear rate for AA8011-TiC- ZrB2 hybrid composite

In current scenario the aircraft industry in need of a lightweight connecting material that persuade the technical and technological standards, but also need superior mechanical qualities. In this work the major objective is to enhance the strength behaviour of stir cast composites. Aluminum 8011 (Al 8011) titanium carbide (TiC) and zirconium boron (ZrB2) hybrid composites are stir cast in this work, and their microstructure, mechanical, and tribological properties are investigated. The matrix material was Al 8011, which was supplemented with stronger TiC to boost mechanical strength and softer ZrB2 to improve thermal and corrosion resistance without significantly changing electrical properties. According to the findings, the reinforced alloy’s mechanical qualities outperform those of the unreinforced alloy. Acoustic energy generated during deformation of composite materials has been monitored and early fracture measurements has been achieved using the Acoustic emission (AE) approach in tensile test specimens. As a result of the experiment, Al8011 + 10% TiC + 2% ZrB2 composites outperform the Al8011 matrix alloy in terms of wear resistance, coefficient of friction, and surface smoothness, as well as other characteristics. The AFM representation of Al8011 + 10% TiC + 2% ZrB2 matrix reveals that the wear surface smoothness of the AMMC is significantly improved as compared to the Al8011 matrix alloys.

Powder-metallurgy fabrication of ZrB2–hardened Zr3Al2 intermetallic composites by high-energy ball-milling and reactive spark-plasma sintering

A powder metallurgy route combining high-energy ball-milling (HEBM) of elemental powders and reactive spark-plasma sintering (SPS) is proposed for the controlled fabrication of novel composites based on a Zr–Al intermetallic matrix hardened with a ceramic second-phase. As proof-of-concept, its suitability is demonstrated on ZrB2–hardened Zr3Al2. Specifically, commercially available powders of ZrH2, Al, and B were first combined in molar ratios of 2:1:1 to give an intermetallic–ceramic composite nominally formed by ∼76.8 vol.% Zr3Al2 plus 23.2 vol.% ZrB2, and were intimately mixed and mechanically activated by HEBM in the form of dry shaker milling for 30 min, next identifying by a dilatometric SPS test at 50 MPa pressure that the densification window of these composites is ∼975–1275 °C. Subsequent densification SPS tests at 50 MPa pressure in that temperature interval, and also at 1350 °C, plus the microstructural and mechanical characterisations of the resulting materials, established 1175 °C as the optimal SPS temperature. It was also identified that densification takes place by transient liquid-phase sintering with molten Al, and that it occurs gradually, not abruptly, because most molten Al disappears in a flash by reacting with Zr to form in situ the intermetallic. It is also shown that the combination of HEBM plus reactive SPS yields Zr3Al2+ZrB2 composites with fine-grained microstructures formed essentially by multitudinous ZrB2 nanograins dispersed within a matrix of submicrometre, or nearly submicrometre, Zr3Al2 grains. Importantly, these intermetallic–ceramic composites were found to be very hard (i.e., ∼11.5 GPa), attributable to the hardening provided by the ZrB2 nanograins, and fairly tough (i.e., ∼4.5 MPa·m1/2), and therefore potential candidate materials for a multitude of structural–tribological applications. Finally, implications for future study are discussed.

Oxidation resistance and emissivity of diboride-based composites containing tantalum disilicide in air plasma up to 2600 K for space applications

Fully-dense ZrB2 and HfB2 composites were elaborated by Spark Plasma Sintering with 20 vol% TaSi2 to replace SiC in the aim of improving their oxidation resistance. This study follows the one carried out on (Zr/Hf)B2–SiC systems in the same oxidation conditions. The oxidation behavior of ZrB2–20%TaSi2 and HfB2-20%TaSi2 in air plasma conditions, at 1000 Pa total pressure and from 1950 K up to 2600 K, was studied using the MESOX facility implemented at the focus of the 6 kW Odeillo solar furnace. The mass variation of the samples during an oxidation duration of 300 s on a temperature plateau was followed. A four step oxidation mechanism is proposed. A good oxidation behavior, with a slight mass gain, has been identified up to 2170 K due to the formation of a refractory mixed oxide (Hf/Zr)6Ta2O17 at the surface of the samples. An improvement of the oxidation resistance by 200 K is obtained compared to the composites with SiC as additional compound. Moreover, as emissivity is an important parameter for space applications and that oxidation plays a huge role on the evolution of the emissivity, the normal spectral emissivity was measured on several pre-oxidized samples using atomic oxygen (representative surfaces) and the normal total emissivity was calculated. Finally, for both the compositions, the emissivity is comprised between 0.80 and 0.90 in the temperature range 1300–2200 K.

Fabrication of C/C–SiC–ZrB2 Ultra-High Temperature Composites through Liquid–Solid Chemical Reaction

In this paper, we aimed to improve the oxidation and ablation resistance of carbon fiber-reinforced carbon (CFC) composites at temperatures above 2000 °C. C/C–SiC–ZrB2 ultra-high temperature ceramic composites were fabricated through a complicated liquid–solid reactive process combining slurry infiltration (SI) and reactive melt infiltration (RMI). A liquid Si–Zr10 eutectic alloy was introduced, at 1600 °C, into porous CFC composites containing two kinds of boride particles (B4C and ZrB2, respectively) to form a SiC–ZrB2 matrix. The effects and mechanism of the introduced B4C and ZrB2 particles on the formation reaction and microstructure of the final C/C–SiC–ZrB2 composites were investigated in detail. It was found that the composite obtained from a C/C–B4C preform displayed a porous and loose structure, and the formed SiC–ZrB2 matrix distributed heterogeneously in the composite due to the asynchronous generation of the SiC and ZrB2 ceramics. However, the C/C–SiC–ZrB2 composite, prepared from a C/C–ZrB2 preform, showed a very dense matrix between the fiber bundles, and elongated plate-like ZrB2 ceramics appeared in the matrix, which were derived from the dissolution–diffusion–precipitation mechanism of the ZrB2 clusters. The latter composite exhibited a relatively higher ZrB2 content (9.51%) and bulk density (2.82 g/cm3), along with lower open porosity (3.43%), which endowed this novel composite with good mechanical properties, including pseudo-plastic fracture behavior.

The effects of in-situ ZrB2 particles and Gd on the solidification behavior and mechanical properties of AA6111 matrix composites

In this research work, the new AA6111 matrix composites reinforced by the cooperation of nano ZrB2 particles and Gd had been designed and fabricated via in situ reaction. The addition of Gd made the nano ZrB2 particles uniformly dispersed due to the reduction of solid-particle interfacial energy (σsp) by keeping the low-energy orientation relationship. Meanwhile, it promotes the formation of equiaxed grains whose formation is also based on the nano-sized reinforcing phases as the hindering of dendrite coherency points are related to the growth restriction factor (GRF) and as the pinning effect to the grain boundaries. The fluidity was improved because of uniform viscosity and dendrites avoided meeting with the neighboring ones by the entrapment of nano-sized reinforcing phases like AlGd and ZrB2. The results indicated that AA6111–0.5 wt. % Gd-2 vol. % ZrB2 composites possessed the longest fluidity length of 70 mm. Meanwhile, the composites displayed increases of 32.7 %, 47.3 % and 52.8 % in YS, UTS and elongation, respectively, compared to the matrix alloy. A notable lattice distortion of the matrix near the ZrB2 particles and AlGd phases was proclaimed via Geometric Phase Analysis (GPA) analysis. Strengthening mechanism comprehending yield strength, containing Orowan strengthening, grain refinement strengthening, was integrally elaborated.

Densification mechanism of spark plasma sintered ZrB2 and ZrB2-SiC ceramic composites

Sintering mechanisms are investigated by determining activation energy of densification (in the temperature range of 1650 °C to 1950 °C) during spark plasma sintering of ZrB2 and SiC-reinforced ZrB2 ceramic composite. The fractured surfaces of sintered composites reveal completely dense microstructures above 1800 °C, whereas porous microstructure prevailed in ZrB2 even after sintering at 1950 °C. Activation energy of 80 ± 16 kJ/mol is obtained for ZrB2 with grain boundary diffusion as governing diffusion mechanism in the temperature range of 1650 to 1950 °C. On the other hand, dominant densification mechanism of grain boundary diffusion (activation energy of 89 ± 19 kJ/mol) estimated in the range of 1650 to 1800 °C changed to lattice diffusion (activation energy of 601 ± 10 kJ/mol) with the addition of 20 vol% SiC in ZrB2. The change of prominent densification mechanism in ZrB2 with SiC, in addition to its impact on the mechanical performance with systemic increase of sintering temperature, is unravelled here.

Processing and characterization of carbon fibres reinforced ZrB2 ultra high temperature ceramic matrix composite

A process technology for the processing of the continuous carbon fibre reinforced ZrB2 (Cf – ZrB2) ultra high temperature ceramic matrix composite (UHTCMC) has been developed. The processing steps are slurry infiltration followed by curing and pyrolysis. The composite was then subjected to high temperature pressureless sintering. The microstrcutural and mechanical properties of Cf – ZrB2 UHTCMC were characterized at the completion of each processing step. The de-lamination between the carbon fibre and the ZrB2 matrix layer in 2D Cf – ZrB2 composite after pressureless sintering was found. However, the problem of de-lamination after sintering was not detected in the 2.5D Cf – ZrB2 composite by stitching the infiltrated layers in the Z-direction. Significant improvements in the sintered density, Young's modulus and flexural strength were achieved through 2.5D Cf – ZrB2 composite.