Zirconium Diboride Silicon Carbide Research Articles

Paste extrusion‐based 3D printing of fiber‐reinforced ultra high‐temperature ceramics

AbstractUltra–high‐temperature ceramics (UHTCs) are valued for their extremely high melting temperatures and resistance to active oxidation. However, their low fracture strengths and the difficulties in shaping them into complex geometries hamper their widespread application. This study aims to fabricate zirconium diboride–silicon carbide (ZrB2‐SiC) composites reinforced with aligned SiC fibers by formulating suspensions containing a preceramic polymer, ZrB2, and SiC fibers. This study assessed the influence of fiber alignment on electrical and thermal conductivities, as well as on mechanical strength. The results revealed a significant enhancement in thermal conductivity, particularly when the fibers were aligned, effectively doubling it compared with the non‐aligned parts. Additionally, increasing the fiber content significantly improved the fracture strength, with composites containing 22.5 vol% fibers reaching fracture strengths over 57 MPa. However, the final values did not meet the theoretical expectations because the porosity in pyrolyzed parts exceeded 10%. Furthermore, the study demonstrated a 10‐fold increase in electrical conductivity with fiber alignment compared to that for non‐aligned composites. These results highlight the capability of paste extrusion‐based additive manufacturing in tailoring ultra–high‐temperature ceramic matrix composites (UHTCMCs) with aligned fibers, realizing their suitability for aerospace applications.

Using Deep Learning to Predict Fracture Patterns in Crystalline Solids

Summary Fracture is a catastrophic process whose understanding is critical for evaluating the integrity and sustainability of engineering materials. Here, we present a machine-learning approach to predict fracture processes connecting molecular simulation into a physics-based data-driven multiscale model. Based on atomistic modeling and a novel image-processing approach, we compile a comprehensive training dataset featuring fracture patterns and toughness values for different crystal orientations. Assessments of the predictive power of the machine-learning model shows excellent agreement not only regarding the computed fracture patterns but also the fracture toughness values and is examined for both mode I and mode II loading conditions. We further examine the ability of predicting fracture patterns in bicrystalline materials and material with gradients of microstructural crystal orientation. These results further underscore the excellent predictive power of our model. Potential applications of this model could be widely applied in material design.

Investigation on machining performance of micro-holes EDM in ZrB2-SiC ceramics using a magnetic suspension spindle system

Zirconium diboride-silicon carbide (ZrB2-SiC) ceramics are considered to be potential candidates for ultra-high temperature (> 2200 °C) applications due to unique combination of properties. However, it is difficult to machine micro-hole in ZrB2-SiC with a high precision by traditional methods owing to its highly mechanical strength. Here, an effective method to machining micro-holes on ZrB2-SiC ceramics was presented, by using a magnetic suspension spindle system (MSSS) electrical discharge machining (EDM) which possesses high response frequency. The objective of this experimental work is to study effects of machining parameters of MSSS EDM on discharge percentage, material removal rate (MRR), electrode wear rate (EWR), and lateral surface quality. Experimental results reveal that compared to micro-holes machined by conventional EDM, with the application of MSSS EDM, discharge percentage increased by at least 28%, and arc percentage decreased by at least 16.3%. Hence, MRR increased by at least 35% and EWR decreased by at least 51%. The inlet and outlet diameters of the micro-holes and the lateral surface of the holes significantly improved with using MSSS EDM. The experimental results demonstrate that compared to conventional EDM, MSSS EDM can be used to fabricate micro-holes on ZrB2-SiC ceramics with a higher efficiency and quality.

An evaluation of the B4C formation in sintered ZrB2-SiC ceramic composites at 2100 °C

The present study was concerned with the high temperature sintering behaviour of zirconium diboride ceramics mixed with fine silicon carbide. Zirconium diboride-silicon carbide (ZrB2-SiC) ceramic composites were pressureless sintered at 2100 °C under flowing argon environment, for a hold time of 150 min. The pressureless sintered ZrB2-SiC pellets were characterized for microstructure and phase analysis. The sintered microstructure was observed through Scanning Electron Microscopy (SEM) embedded with Energy Dispersive Spectroscopy (EDS) and different phases were analyzed through X-ray Diffraction (XRD). The investigation revealed the presence of boron carbide (B4C) within the sintered pellets containing 20 mol.% SiC. The B4C was formed during sintering without the presence of any free carbon as part of initial powder mixture. Possible routes to identify and explain the formation of B4C in the absence of free carbon were discussed.

Oxidation protection and behavior of in-situ zirconium diboride–silicon carbide coating for carbon/carbon composites

To protect carbon/carbon (C/C) composites against oxidation, zirconium diboride–silicon carbide (ZrB2–SiC) coating was prepared by in-situ reaction using ZrC, B4C and Si as raw materials. The in-situ ZrB2–SiC coated C/C presented good oxidation resistance, whose weight loss was only 0.15% after isothermal oxidation at 1500°C for 216h. Microstructure evolution of coating at 1500°C was studied, revealing a two-layered structure: (1) ZrO2 (ZrSiO4) embedded in SiO2-rich glass, and (2) unaffected ZrB2–SiC. The formation and collapse of bubbles influenced the coating oxidation greatly. A model based on the evolution of oxide scale was proposed to explain the failure mechanism of coating.

Mechanical behavior of zirconium diboride–silicon carbide–boron carbide ceramics up to 2200°C

The mechanical properties of hot pressed zirconium diboride–silicon carbide–boron carbide (ZrB 2 –SiC–B 4 C) ceramics were characterized from room temperature up to 2200 °C in an argon atmosphere. The average ZrB 2 grain size was 3.0 μm. The SiC particles segregated into clusters, and the largest clusters were >30 μm in diameter. The room temperature flexural strength was 700 MPa, decreasing to 540 MPa at 1800 °C and to 260 MPa at 2200 °C. The strength was controlled by the SiC cluster size up to 1800 °C. At higher temperatures, strength was controlled by formation of liquid phases, and precipitation of large BN and B–O–C–N inclusions. The mechanical behavior of these materials changes at ∼1800 °C, meaning that extrapolation of properties from lower temperatures is not accurate. Mechanical behavior in the ultra-high temperature regime was dominated by impurities and changes in microstructure. Therefore, the use of higher purity materials could lead to significant improvements in ultra-high temperature strength.

A Novel Technique for the Determination of Surface Biaxial Stress under External Confinement Using Raman Spectroscopy

Bi-axial compressive stress induced as a result of mechanical confinement within a zirconium diboride-silicon carbide (ZrB2-SiC) ceramic composite has been quantified using micro Raman spectroscopy and then validated using two independent experimental methods. First a relationship relating the Raman peak-shift on a confined silicon carbide (SiC) particle to magnitude of imposed confinement stress was developed by utilizing phonon deformation potentials for 3C-SiC diamond and zinc-blende crystal structures. ZrB2-5wt%SiC samples, prepared using spark plasma sintering were subjected to different confinement pressure on the lateral surface by thermal shrink fitting metallic sleeves. The relationship between Raman peak-shift and confinement stress was then verified by comparing the measured stress in this method with that calculated from analytical expressions readily available for thick walled cylinders. The relationship was further validated independently using digital image correlation (DIC) by measuring the displacements for unknown levels of progressively increasing confinement stress induced by a shaft-collar ring on similar specimens. The Raman peak-shift relation derived for SiC phase also correctly predicted process-induced residual stresses due to a mismatch in coefficient of thermal expansion between the matrix phase and SiC particles. The derived Raman peak-shift relationship can also be generalized and can be a valuable tool to experimentally determine unknown bi-axial stress in a Raman active structure.

ZrB2-SiC Coatings Prepared by Vapor and Liquid Silicon Infiltration Methods: Microstructure and Oxidation Resistance Property

Novel zirconium diboride-silicon carbide (ZrB2-SiC) coatings were prepared by vapor silicon infiltration (VSI) and liquid silicon infiltration (LSI), respectively. The static oxidation resistance properties of these coatings were evaluated and their microstructure evolution during oxidation was studied. It showed that the VSI coating had better oxidation resistance than LSI. A compact oxide scale was formed on the VSI coating, which strongly suppressed fur- ther oxidation damage during the testing. The poor oxidation resistance of the LSI coating could be mainly attributed to micro-cracks and residual silicon.

Mechanical behavior of zirconium diboride–silicon carbide ceramics at elevated temperature in air

The mechanical properties of zirconium diboride–silicon carbide (ZrB 2 –SiC) ceramics were characterized from room temperature up to 1600 °C in air. ZrB 2 containing nominally 30 vol% SiC was hot pressed to full density at 1950 °C using B 4 C as a sintering aid. After hot pressing, the composition was determined to be 68.5 vol% ZrB 2 , 29.5 vol% SiC, and 2.0 vol% B 4 C using image analysis. The average ZrB 2 grain size was 1.9 μm. The average SiC particles size was 1.2 μm, but the SiC particles formed larger clusters. The room temperature flexural strength was 680 MPa and strength increased to 750 MPa at 800 °C. Strength decreased to ∼360 MPa at 1500 °C and 1600 °C. The elastic modulus at room temperature was 510 GPa. Modulus decreased nearly linearly with temperature to 210 GPa at 1500 °C, with a more rapid decrease to 110 GPa at 1600 °C. The fracture toughness was 3.6 MPa·m ½ at room temperature, increased to 4.8 MPa·m ½ at 800 °C, and then decreased linearly to 3.3 MPa·m ½ at 1600 °C. The strength was controlled by the SiC cluster size up to 1000 °C, and oxidation damage above 1200 °C.

Stress measurements in ZrB 2–SiC composites using Raman spectroscopy and neutron diffraction

Raman spectroscopy and neutron diffraction were used to study the stresses generated in zirconium diboride–silicon carbide (ZrB 2–SiC) ceramics. Dense, hot pressed samples were prepared from ZrB 2 containing 30 vol% α-SiC particles. Raman patterns were acquired from the dispersed SiC particulate phase within the composite and stress values were calculated to be 810 MPa. Neutron diffraction patterns were acquired for the ZrB 2–SiC composite, as well as pure ZrB 2 and SiC powders during cooling from ∼1800 °C to room temperature. A residual stress of 775 MPa was calculated as a function of temperature by comparing the lattice parameter values for ZrB 2 and SiC within the composite to those of the individual powders. The temperature at which stresses began to accumulate on cooling was found to be ∼1400 °C based on observing the deviation in lattice parameters between pure powder samples and those of the composite.

Liquid Oxide Flow during Oxidation of Zirconium Diboride-Silicon Carbide Ultra High Temperature Ceramics

Recent ideas on the oxidation of ZrB2-SiC are presented, emphasizing the behavior of the boria-silica-zirconia liquid (BSZ liquid) which forms during oxidation and flows to transport silica and zirconia to the surface of the scale. Oxide film microstructure is strongly influenced by the boron oxide, which acts as a volatile flux.

In situ microscopy observation of liquid flow, zirconia growth, and CO bubble formation during high temperature oxidation of zirconium diboride–silicon carbide

The oxidation of ZrB 2–SiC composites at 1450–1650 °C was directly observed with in situ optical microscopy. Video frames showed the flow of silicate liquids, the formation of zirconia deposits, and the growth and collapse of gaseous bubbles on the oxide surface. Contrast in the incandescence of in situ images is analyzed as spatial variations in hue and intensity and related to differences in emissivity of the oxide scale surface features by comparing these hot images with room temperature images. Above 1450 °C, gaseous bubbles were observed to grow and collapse causing perturbations in the liquid oxide on the surface. The bubbles are associated with the evolution of CO from SiC oxidation and the onset is related to the critical temperature where the partial pressure of CO under the oxide scale exceeds atmospheric pressure.

Formation of Oxide Scales on Zirconium Diboride–Silicon Carbide Composites During Oxidation: Relation of Subscale Recession to Liquid Oxide Flow

The formation of oxide scales on zirconium diboride (ZrB2)–silicon carbide (SiC) composites oxidized at high temperatures (>1500°C) is studied. Subscale recession found in oxidized ZrB2 composites is proposed to form due to flow of boron oxide (boria) (B2O3)‐rich borosilicate liquid through convection cells that form upon oxidation of the composite at high temperatures. The flow of the B2O3‐rich liquid to the surface, with the subsequent loss of B2O3 to evaporation, explains the formation of a glassy silica‐rich layer on the surface commonly reported in the literature. Also the outward flow of the liquid creates a localized inward path for oxygen due to lower viscosity that allows faster oxidation under the convection cells which creates the subscale recession. Optical and electron micrographs of a ZrB2–15%SiC composite oxidized at 1550°C are presented as evidence of flowing liquids. Micrographs of oxide scale deformations are also presented, which are proposed to be related to the formation of oxide scale features called convection cells. The subscale recession and oxide scale deformations of ZrB2–15%SiC composites oxidized for 3 and 4 h at 1550°C were studied with microstructure and chemical composition analysis.

Recent Advances in Dynamic Indentation Fracture, Impact Damage and Fragmentation of Ceramics

In this feature article, dynamic indentation‐induced deformation and fracture phenomena in brittle solids are related to the deformation behavior and fracture patterns evolved during dynamic impact on structural ceramics. Examples of indentation‐induced localized amorphization in boron carbide (B4C) and differences in fracture characteristics due to static and dynamic indentations on B4C and zirconium diboride–silicon carbide (ZrB2–SiC) ceramic composite are presented. These features are compared with the fracture patterns evolved during the high‐velocity ball impact on SiC. The influences of processing‐induced (inherent) flaws and deformation‐induced flaws on fracture initiation in a brittle material are discussed. Recent developments in analytical modeling of indentation‐ and impact‐induced damage in ceramics and computational efforts on fracture and fragmentation response of ceramics are thoroughly reviewed. Finally, some future research directions are identified.

Zirconia Transport by Liquid Convection during Oxidation of Zirconium Diboride–Silicon Carbide

During high‐temperature oxidation of ZrB2–SiC composites, a multi‐layer oxide scale forms with a silica‐rich borosilicate liquid as the surface oxide layer. Here, a recently proposed novel mechanism for the high‐temperature oxidation of ZrB2–SiC composites is further investigated and verified. This mechanism involves the formation of convection cells in the oxide surface layer during high‐temperature oxidation of the composite. The formation of zirconia deposits found in the center of the convection cells is proposed here to be the consequence of liquid transport. The nature and deposition mechanism of the zirconia is reported in detail, using calculated phase equilibrium diagrams and microstructure observations of a ZrB2‐15 vol% SiC composite tested at 1550° and 1700°C in ambient air for various times. The calculated phase equilibrium diagrams for the binary ZrO2–B2O3 system as well as the ternary B2O3–SiO2–ZrO2 system at 1500°C are reported here to interpret these results.

Evolution of structure during the oxidation of zirconium diboride–silicon carbide in air up to 1500 °C

The structures that developed as dense ZrB 2–SiC ceramics were heated to 1500 °C in air were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. The oxidation behavior was also studied using thermal gravimetric analysis (TGA). Below 1200 °C, a protective B 2O 3-rich scale was observed on the surface. At 1200 °C and above, the B 2O 3 evaporated and the SiO 2-rich scale that formed was stable up to at least 1500 °C. Beneath the surface, layers that were rich in zirconium oxide, and from which the silicon carbide had been partially depleted, were observed. The observations were consistent with the oxidation sequence recorded by thermal gravimetric analysis.

Low‐Temperature Densification of Zirconium Diboride Ceramics by Reactive Hot Pressing

Zirconium diboride–silicon carbide ceramics with relative densities in excess of 95% were produced by reactive hot pressing (RHP) at temperatures as low as 1650°C. The ZrB2 matrix was formed by reacting elemental zirconium and boron. Attrition milling of the starting powders produced nanosized (<100 nm) Zr particulates that reacted with B below 600°C. The reaction resulted in the formation of nanoscale ZrB2 crystallites that could be densified more than 250°C below the temperatures required for conventional ZrB2 powder. Because of the low‐temperature densification, the resulting ZrB2 grain sizes were as small as 0.5±0.30 μm for specimens densified at 1650°C and 1.5±1.2 μm for specimens densified at 1800°C. Vickers hardness, elastic modulus, and flexure strength of fully dense materials produced by RHP were 27, 510, and 800 MPa, respectively.

Influence of silicon carbide particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide ceramics

The influence of silicon carbide (SiC) particle size on the microstructure and mechanical properties of zirconium diboride–silicon carbide (ZrB 2–SiC) ceramics was investigated. ZrB 2-based ceramics containing 30 vol.% SiC particles were prepared from four different α-SiC precursor powders with average particle sizes ranging from 0.45 to 10 μm. Examination of the dense ceramics showed that smaller starting SiC particle sizes led to improved densification, finer grain sizes, and higher strength. For example, ceramics prepared from SiC with the particle size of 10 μm had a strength of 389 MPa, but the strength increased to 909 MPa for ceramics prepared from SiC with a starting particle size of 0.45 μm. Analysis indicates that SiC particle size controls the strength of ZrB 2–SiC.

Oxidation of Zirconium Diboride–Silicon Carbide at 1500°C at a Low Partial Pressure of Oxygen

The oxidation behavior of zirconium diboride containing 30 vol% silicon carbide particulates was investigated under reducing conditions. A gas mixture of CO and ∼350 ppm CO2 was used to produce an oxygen partial pressure of ∼10−10 Pa at 1500°C. The kinetics of the growth of the reaction layer were examined for reaction times of up to 8 h. Microstructures and chemistries of reaction layers were characterized using scanning electron microscopy and X‐ray diffraction analysis. The kinetic measurements, the microstructure analysis, and a thermodynamic model indicate that oxidation in CO–CO2 produced a non‐protective oxide surface scale.

Boron carbide and nitride as reactants for in situ synthesis of boride-containing ceramic composites

Using boron carbide (B 4C) and boron nitride (here refers to hexagonal BN) as reactants, a series of boride-containing ceramic composites, mainly in the present work zirconium diboride-containing composites including zirconium diboride–zirconium carbide (ZrB 2–ZrC), zirconium diboride–zirconium nitride (ZrB 2–ZrN), zirconium diboride–silicon carbide (ZrB 2–SiC) and zirconium diboride–aluminum nitride (ZrB 2–AlN) were prepared by in situ reactive hot pressing. The features and the development mechanisms of the composite microstructures were characterized and modeled. The obtained zirconium diboride-containing composites demonstrated high bending strength. In addition, some general problems such as transformation between B 4C and BN and thermodynamics of using B 4C and BN as reactants were also briefly discussed.