Toughness Of Ceramics Research Articles

Excellent energy storage properties in ZrO2 toughened Ba0.55Sr0.45TiO3-based relaxor ferroelectric ceramics via multi-scale synergic regulation

Lead-free ceramic capacitors offer ultrahigh power density and ultrafast discharging rates, making them critical energy storage components for advanced pulsed power systems. However, the greatest obstacle to broader applications remains the relatively low energy storage density. In this study, a relaxor ferroelectric ceramic based on (0.6-x)Ba0.55Sr0.45TiO3-0.4Bi0.5Na0.5TiO3-xSrZrO3 ((0.6-x)BST-0.4BNT-xSZ) is prepared using the tape casting method, resulting in an excellent energy density (Wrec ≈ 10.0 J cm−3) and high energy storage efficiency (η ≈ 91 %). The solid solution of linear dielectrics SrZrO3 synergistically regulates both relaxor properties and breakdown strength. The variation of relaxor property was explored utilizing New Glass model and the multi-polarization model, with confirmation provided by piezoresponse force microscopy. Furthermore, the breakdown strength could be attributed to improvements in electric insulation and the widening of the bandgap. As SrZrO3 content increases, the in-situ emergence of the second phase ZrO2, accompanied by a martensitic transformation, not only improves the fracture toughness of ceramics but also serves to elongate the breakdown path. Encouragingly, x = 0.20 ceramics also achieve excellent temperature stability (−95–125 ℃), frequency stability (1–1000 Hz), cycling reliability (1–106 cycles), and great charging-discharging properties. This multiscale synergic regulation strategy plays a guiding role in the screening of high-performance energy storage dielectric materials.

Significantly improved mechanical properties of mullite ceramics by adding AlOOH with different sizes and morphologies

AbstractMullite ceramics with high purity and toughness were prepared by hot‐press sintering of pyrophyllite at 1300°C using AlOOH nanomaterials with different sizes and morphologies (nanoparticles, nanorods, nanoflakes, and micro‐sized sea urchin–like) as additives. Among the four types of AOOH additives, the incorporation of nanoflakes and sea urchins resulted in the formation of a relatively uniformly distributed and tightly packed microstructure within the ceramics, which significantly improved the density and mechanical properties of the ceramic materials. Compared to nano‐sized AlOOH, the addition of micron‐sized sea urchin–like AlOOH could produce mullite ceramics with best purity and flexural strength. The flexural strength and fracture toughness of ceramics prepared from micro‐sized sea urchin–like AlOOH and pyrophyllite reach 427.34 ± 1.99 MPa and 4.68 ± .31 MPa m1/2, respectively. During the ball milling process, the originally micron‐sized sea urchin–like AlOOH particles were broken down into micro‐ and nano‐sized AlOOH particles. The resulted micron and nanoscale AlOOH particles exhibited synergistic and multi‐scale effects with pyrophyllite, which contributed to the formation of uniformly sized and densely arranged mullite crystals within the ceramics. Additionally, the bridging between the mullite crystals further improved the mechanical properties of the mullite ceramic material.

Influence of polycarbosilane composition on the properties of SiC/SiC composite fabricated by precursor infiltration and pyrolysis process

AbstractA series of SiC/SiC composites were fabricated through the precursor infiltration and pyrolysis (PIP) process, using solid polycarbosilane (PCS) and liquid vinyl perhydrogen PCS (VHPCS) solutions as impregnating agents. The physicochemical characteristics of the SiC matrices derived from PCS and VHPCS were investigated and compared. The impact of the PCS composition on the microstructure, density, flexural strength, and modulus of the resulting SiC/SiC composites was also examined. As the VHPCS content increased to 60 wt%, the flexural strength of the composites gradually rose to a peak of 490.9 MPa before decreasing as the VHPCS proportion continued to increase. Meanwhile, the flexural modulus increased continually with the introduction of VHPCS. A possible mechanism is proposed to explain the different variations in flexural strength and modulus, taking into account the ceramic toughening principle and the distinct properties of PCS and VHPCS.

Digital light processing‐based additive manufacturing of orientation‐controlled Al2O3 ceramics with improved damage tolerance

AbstractDigital light processing (DLP) provides a promising avenue for constructing ceramic parts with high precision and complex shapes, yet the inherent brittleness and strength‐toughness trade‐off hinder their wide applications. Here, according to DLP 3D printing, the textured alumina ceramic components with horizontally aligned textured microstructure were successfully created by adding anisotropically shaped platelets. As a critical process in the preparation of textured ceramics, the alumina platelets were aligned horizontally during printing by using the special shear fields and forming capabilities of DLP technology. The shrinkage, density, microstructure, mechanical performance, and damage‐tolerance behavior of alumina parts with different platelet concentrations were examined, and the toughening mechanisms were investigated. The strength and toughness of ceramics with 5 vol.% platelet addition are increased by 22% and 43%, respectively, as compared with those without platelets. The improved damage tolerance capabilities were primarily ascribed to the collaborative toughening mechanisms stimulated by the platelet addition, including crack branching, crack deflection, uncracked‐ligament bridging, and platelet pull‐out, which increased the crack tortuosity and consumed more fracture energy. The strategy opens up new opportunities to design complex 3D ceramic geometries with bio‐inspired layered or textured architectures, providing optimized damage tolerance.

Atomistic Investigation of Grain Boundary Fracture in Alumina.

Grain boundary (GB) fracture is a major mechanism of material failure in polycrystalline ceramics. However, the intricate atomic arrangements of GBs have impeded our understanding of the atomistic mechanisms of these processes. In this study, we investigated the atomic-scale crack propagation behavior of an α-Al2O3 ∑13 grain boundary, using a combination of in situ transmission electron microscopy (TEM) and scanning TEM. The atomic-scale fracture path along the GB core was directly determined by the observation of the atomic structures of the fractured surfaces, which is consistent with density functional theory calculations. We found that the GB fracture can be attributed to the weaker local bonds and a smaller number of bonds along the fracture path. Our findings provide atomistic insights into the mechanisms of crack propagation along GBs, offering significant implications for GB engineering and the toughening of ceramics.

Activating continuous dislocation pinning enhanced toughness of nanocomposite coating through specially oriented semicoherent heterointerface lattice distortion

Ionic crystal ceramics are known to be susceptible to brittle cracks along the intergranular due to the strong ionic bond forces. Accordingly, an outstanding toughened coating consisting of yttria-stabilized tetragonal zirconia (YSTZ) and MgO, with a reinforced heterointerface, has been successfully achieved through the plasma electrolytic oxidation process. The results demonstrate that the enhanced Zr/Y–O bond strength improves the interfacial strength of the ionic crystal, while the lattice distortion activates continuous dislocation pinning at the (101) YSTZ//(111) MgO semicoherent heterointerface effectively hinders crack propagation of the coating. With the YSTZ content approaching 65 %, the toughness (KIC) value surpasses that of PEO coating by 42 %. These findings not only elucidate the scientific foundation for the improved toughness of the YSTZ/MgO nanocoating but also provide valuable insights into design strategies for improving ceramic toughness.

Сравнительный анализ структуры и свойств керамик на основе оксида алюминия, полученных методами свободного и электроимпульсного плазменного спекания

The effect of the initial size of alumina particles on the density, microstructure, hardness, and fracture toughness of ceramics obtained by conventional and spark plasma sintering (SPS) has been studied. We studied ceramics obtained from commercial Al2O3 powders with an initial particle size of 40 – 50 nm, 0.2 mm, and 1 mm, and domestic fine powders with an initial particle size of 0.2 – 3 mm, and Al2O3 + 0.25 vol. % MgO and Al2O3 + 10 vol. % ZrO2. It is shown that the density of alumina ceramics nonmonotonically depends on the initial size of Al2O3 powder particles. It has been established that an increase in the grain size leads to a nonmonotonic change in the hardness of alumina ceramics. It has been established that the addition of 0.25 vol. % MgO accelerates the sintering of alumina. The addition of 10 vol. % ZrO2 makes it possible to provide an optimal combination of hardness and fracture toughness. It is shown that fine-grained ceramics obtained by the SPS method have a higher hardness. It has been suggested that SPS of submicron alumina powders with an amorphous layer on the surface, additionally stabilized by zirconia particles, is promising for further increasing the hardness of alumina ceramics.

Polymer-derived W-doping (Zr, Hf, Nb, Ta)C high entropy ceramics: Preparation, Properties and DFT calculation

(Zr, Hf, Nb, Ta, W)C high entropy carbides nano-powders (average particle size less than 65 nm) with low oxygen content (0.2–1.4 wt%) were synthesized through pyrolysis of polymer precursors. Bulk ceramics were fabricated through the process of hot-pressing, and their characteristics were studied by both computational and experimental methods. Density functional theory was carried out to analyze the effects of defects and the W element on the melting point, hardness, modulus, and toughness of ceramics. The results showed that W content had limited influence on the melting points and the aforementioned mechanical properties of ceramics, while carbon vacancies lead to a significant decrease in melting point, hardness and modulus, with slight increases in toughness. Experimental results indicated that the grain size, grain boundary strength, and lattice distortion of ceramic bulks increased with the increase of W content, which affected the mechanical properties consequently. Ceramics with W content of 5 mol% exhibited the best experimental comprehensive performances, with the Vickers hardness, fracture toughness and flexural strength of 23.82 ± 0.49 GPa, 5.66 ± 0.22 MPa·m1/2 and 593.95 ± 15.71 MPa, respectively.

A residual stress-dependent mixed-mode phase-field model: Application to assessing the role of tailored residual stresses on the mechanical performance of ceramic laminates

Ceramics offer several attractive properties of industrial relevance, e.g. high strength and hardness, low thermal conductivity, and chemical inertness in critical environments. There is thus interest among researchers to improve the fracture toughness of ceramics, which is generally low and considered a major drawback. Numerous experimental studies in the literature report on the enhancement of mechanical performance of ceramic laminates, especially fracture toughness, by tailoring the residual stress, resulting in crack deflection or bifurcation. However, there is a dearth of computational models that can reliably predict the crack path and accurately quantify the improved fracture toughness. In this article, we propose a residual stress-dependent mixed-mode phase-field model within a small deformation set-up. The proposed model is efficient in including any energy dissipation effect in a consistent manner. The model can be exploited as a tool to study the effect of tailored residual stresses on the fracture toughness of ceramic laminates. We have validated our proposal by reproducing the results for a few problems that require the incorporation of residual stresses within the formulation. By conducting a set of four-point bending tests on notched composite beams made of alternating layers of Al2O3 with 5% tetragonal ZrO2 (ATZ) and Al2O3 with 30% monoclinic ZrO2 (AMZ), we demonstrate how tailored residual stresses could indeed influence the mechanical performance of ceramic laminates.

Defects control of silicon nitride ceramics by oscillatory pressure sintering and consequent hot isotropic pressing

Micro-pores and micro-cracks inhibit the enhancement in strength and toughness of structural ceramics. Among various processing procedures, sintering is the key stage to control microstructure and then enhance mechanical performances of ceramics. Here, we reported the consolation of silicon nitride ceramics with high strength and toughness by defects control, using oscillatory pressure sintering (OPS) followed by hot isostatic pressing (HIP) techniques. The introduction of oscillatory pressure and isostatic pressure may enhance grain sliding and grains deformation of during sintering, thus removed the trapped pores at grain boundaries and accelerated growth of β-Si3N4 grains. Because of the microstructure evolution, the Si3N4 ceramics exhibited flexural strength of 1630 ± 21 MPa and fracture toughness of 7.1 ± 0.6 MPa m1/2 when sintered at 1750 °C. Thus, this work provides a path to prepare ultra-strong and tough ceramics by controlling various micro-defects.

Low-yttria doped zirconia: Bridging the gap between strong and tough ceramics

Low-yttria doped zirconia: Bridging the gap between strong and tough ceramics

A review of armour's use of composite materials

Composites with a laminated structure come from stacking ceramic and metal in a particular order. Because of their high strength and hardness, low density of ceramics, and extraordinary flexibility, metals can be used as bulletproof armour. The bullet anti-penetration system includes a ceramic screen that slows down the projectile and splits it up and a metal backplate that plastically deforms to absorb the projectile's kinetic energy. Laminates have several downsides, including weak interface bonding, a tendency for tip cracks due to increased internal stress, and a jarring difference between the metal and ceramic properties. Crack migration and propagation can cause abrupt changes in material characteristics at the ceramic–metal contact. A drop between the ceramic panel and metal backplate can be easily triggered when a ceramic panel is impacted, as cracks form in the interlayer. In this area, the interface bonding strength is still inadequate. In this review, we looked at the meshless smoothed-particle hydrodynamic method for high-velocity impact and massive deformation, the finite-element simulations of interface impact resistance and the first-principles predictions of interface strength. The paper concludes with numerous suggestions for future improvement: Further study is required on ceramic toughening to increase the compatibility of ceramic panels and metal backplates, the performance transition between ceramic and metal, and the reliability of ceramic–metal laminated materials. It is critical to study ways to strengthen metals. More multiscale research using methods like the phase-field method, finite element analysis, and first-principles computations, focusing on how to mix these techniques naturally and successfully, is needed to reinforce metals by introducing nano-phases into metal matrix composites while still retaining the metal's ductility. The latest study that emphasises the potential advantages of hybrid materials, specifically the combination of aramid and kenaf fibres, highlights a notable progression in the domain of armour technology.

Surface preparation for characterization of nitride compound layers using hardness indentation and the Palmqvist method

The Palmqvist method is usually used as a measure to evaluate the toughness of ceramics and thin coatings, as these cannot be determined with classic test methods such as the tensile test or the Charpy impact test due to their brittleness or the small proportion of the coating in the specimen volume. Nitride compound layers, formed during nitriding and nitrocarburizing, are also brittle and only have a thickness of a few micrometers, so determining their toughness is also challenging. In this work, compound layers with different phase compositions and thicknesses were investigated on EN31CrMoV9 and EN42CrMo4 steels using the Palmqvist method. Barrel finishing and polishing were used for specimen preparation, for which a significant effect on the formation of Palmqvist cracks was found. Barrel finishing reduced the length of the Palmqvist cracks with increasing barrel finishing time until a constant level was reached. The surface condition caused by the porosity near the surface of the compound layer was identified as another influencing factor, thus the pore seam was removed for the further investigations. Various specimen variants were prepared and their phase compositions and compound layer thicknesses evaluated in relation to the crack lengths of the Palmqvist cracks. A correlation was found between the length of the Palmqvist cracks and the extent of the compound layer thickness.

Fabrication of strong and tough alumina ceramic with isotropic textured microstructure at low temperature

High strength and toughness are contradictory in ceramic materials. Improving the toughness of ceramics through the introduction of a ductile phase to dissipate energy is usually at the sacrifice of strength, stiffness, and the ability to operate at high temperature. Here we developed a simple approach to fabricate isotropic alumina monolithic ceramic characterized by a unique combination of high strength (405.4 MPa), high toughness (5.62 MPa m1/2) and thermal shock resistance toughness (746.2 °C), displaying a non-brittle fracture behavior. A clear picture of the toughening mechanism was depicted. This work highlights a practical guideline for development of bioinspired structural alumina ceramic.

Mixed-mode fracture model to quantify local toughness in nacre-like alumina

With the progress of ceramic engineering, tough technical ceramics such as nacre-like alumina now exhibit complex fracture patterns with high degrees of deflection, branching and bridging. If these mechanisms highly contribute to improving crack resistance, the crack geometries go beyond the hypotheses assumed in standard techniques to quantify toughness, making it difficult to understand the mechanisms responsible for crack propagation. We report a robust local solution based on a combination of analytical formulas and finite element analysis to accurately estimate the effective stress intensity factors at the tips of multiple deflected cracks. The influence of sample size on local R-curves is analysed and shown to be less important relative to standard methods. We use this method to evaluate the direct influence of zirconia nanoparticles in the nacre-like structure and highlight the role of these findings in the understanding of mechanical response and future optimisation of highly textured tough ceramics.

Toughening Ceramics down to Cryogenic Temperatures by Reentrant Strain-Glass Transition.

Ceramics, often exhibiting important functional properties like piezoelectricity, superconductivity, and magnetism, are usually mechanically brittle at room temperature and even more brittle at low temperature due to their ionic or covalent bonding nature. The brittleness in their working temperature range (mostly from room down to cryogenic temperatures) has been a limiting factor for the usefulness of these ceramics. In this Letter, we report a surprising "low-temperature toughening" phenomenon in a La-doped CaTiO_{3} perovskite ceramic, where a 2.5× increase of fracture toughness K_{IC} from 1.9 to 4.8 MPa m^{1/2} occurs when cooling from above room temperature (323K) down to a cryogenic temperature of 123K, the lowest temperature our experiment can reach. In situ microscopic observations in combination with macroscopic characterizations show that this desired but counterintuitive phenomenon stems from a reentrant strain-glass transition, during which nanosized orthorhombic ferroelastic domains gradually emerge from the existing tetragonal ferroelastic matrix. The temperature stability of this unique microstructure and its stress-induced transition into the macroscopic orthorhombic phase provide a low-temperature toughening mechanism over a wide temperature range and explain the observed phenomenon. Our finding may open a way to design tough ceramics with a wide temperature range and shed light on the nature of reentrant transitions in other ferroic systems.

Enhancing hardness and toughness of WC simultaneously by dispersed ZrO2

A novel method was proposed to achieve uniform dispersion of ZrO2 nanoparticles in the WC matrix. The prepared WC-ZrO2 ceramic exhibited outstanding mechanical properties with simultaneously high hardness and fracture toughness. It was disclosed that the high toughness of the present WC-ZrO2 ceramic results from the contributions of stress-induced phase transformation from t-ZrO2 to m-ZrO2, the homogeneous ultrafine microstructure with coherent WC/ZrO2 interface, and the stress release of WC in the vicinity of ZrO2. The later two factors enhance the fracture toughness by crack deflection and crack bridging. In particular, the contribution to toughness by phase transformation of ZrO2 is 1.9 and 2.7 times of that of the crack deflection and crack bridging, respectively. This study provides a strategy to increase toughness of ceramics greatly while keeping its high hardness.

Spark Plasma Sintering of Ceramics Based on Solid Solutions of Na1+2xZr2−xCox(PO4)3 Phosphates: Thermal Expansion and Mechanical Properties Research

The structure, microstructure, coefficient of thermal expansion (CTE), and mechanical properties of Na1+2xZr2−xCox(PO4)3 ceramics (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were studied. Na1+2xZr2−xCox(PO4)3 submicron powders with the NaZr2(PO4)3 structure (NZP, kosnarite type) were obtained by the solid-phase method. The starting reagents (NaNO3, ZrOCl2·8H2O, NH4H2PO4, CoCl2·6H2O, ethanol) were mixed with the addition of ethyl alcohol. The resulting mixtures were annealed at 600 °C (20 h) and 700 °C (20 h). The obtained phosphates crystallized in the expected structure of the NaZr2(PO4)3 type (trigonal system, space group R3¯c). Thermal expansion of the powders was studied with high-temperature X-ray diffraction at temperatures ranging from 25 to 700 °C. CTEs were calculated, and their dependence on the cobalt content was analyzed. Na1+2xZr2−xCox(PO4)3 ceramics with high relative density (93.67–99.70%) were obtained by Spark Plasma Sintering (SPS). Ceramics poor in cobalt (x = 0.1) were found to have a high relative density (98.87%) and a uniform fine-grained microstructure with a grain size of 0.5–1 µm. Bigger cobalt content leads to a smaller relative density of ceramics. During the sintering of ceramics with high cobalt content, anomalous grain growth was observed. The powder compaction rate was shown to be determined by creep and diffusion intensity in the Na1+2xZr2−xCox(PO4)3 crystal lattice. SPS activation energy in ceramics increased as the cobalt content grew. The microhardness and fracture toughness of ceramics did not depend on their cobalt content.

B4C-based hard and tough ceramics densified via spark plasma sintering using a novel Mg2Si sintering aid

Full-dense B 4 C-based ceramics with excellent mechanical properties were fabricated using spark plasma sintering with Mg 2 Si as a sintering aid at a low temperature of 1675 °C while applying a uniaxial pressure of 50 MPa. The effect of Mg 2 Si addition on the densification behaviours, mechanical properties and microstructure of as-sintered ceramics were investigated. Not only did the formation of ultra-fine grained SiC using the in-situ reaction effectively inhibit the growth of B 4 C grains, but it also contributed to the strength and toughness of the resultant ceramics. Additionally, microalloying Mg imparted more metal bonding characteristics to the B 4 C matrix, thereby improving their ductility. The results indicate that the composite containing 7 wt% Mg 2 Si had excellent mechanical properties, including a light weight of 2.54 g/cm 3 , Vickers hardness of 34.3 GPa, fracture toughness of 5.09 MPa m 1/2 and flexural strength of 574 MPa.

Fluctuation-based fracture mechanics of heterogeneous materials.

We present results of a hybrid analytical-simulation investigation of the fracture resistance of heterogeneous materials. We show that bond-energy fluctuations sampled by Monte Carlo simulations in the semigrand canonical ensemble provide a means to rationalize the complexity of heterogeneous fracture processes, encompassing probability and percolation theories of fracture. For a number of random and textured model materials, we derive upper and lower bounds of fracture resistance and link bond fracture fluctuations to statistical descriptors of heterogeneity, such as two-point correlation functions, to identify the origin of toughening mechanisms. This includes a shift from short- to long-range interactions of bond fracture processes in random systems to the transition from critical to subcritical bond fracture percolation in textured materials and the activation of toughness reserves at compliant interfaces. Induced by elastic mismatch, they connect to a number of disparate experimental observations, including toughening of brittle solids by deformable polymers or organics in, e.g., gas shale, nacre; stress-induced transformational toughening in ceramics; and toughening of sparse elastic networks in hydrogels, to name a few.