Design and fabrication of Si3N4/(W,Ti)C graded nano-composite ceramic tool materials

Si₃N₄/(W, Ti)C graded nano-composite ceramic tool materials with different thickness ratios and number of layers were fabricated by hot pressing technology. The flexural strength, fracture toughness and hardness of the sintered composites were tested and the microstructure and indention cracks were observed. The experiment results showed that the five-layer graded nano-composites with a thickness ratio of 0.2, which were sintered under a pressure of 30 MPa at 1700 °C in vacuum condition for 45 min, had the optimum comprehensive mechanical properties with a flexural strength of 1080.3 MPa, a hardness of 17.64 GPa, and a fracture toughness of 10.87 MPa·m^1/2. The formation of elongated β-Si₃N₄ grains contributes to the favorable mechanical properties. The graded structure can induce residual compressive stress in the surface layer and enhance the mechanical properties. The strengthening and toughening mechanisms are a synergistic effect of intergranular and transgranular fracture, crack bridging and deflection.     

Microstructure,mechanical properties and toughening mechanisms of graphene reinforced Al2O3-WC-TiC composite ceramic tool material

The low fracture toughness of Al₂O₃-based ceramics limited their practical application in cutting tools. In this work, graphene was chosen to reinforce Al₂O₃-WC-TiC composite ceramic tool materials by hot pressing. Microstructure, mechanical properties and toughening mechanisms of the composite ceramic tool materials were investigated. The results indicated that the more refined and denser composite microstructures were obtained with the introduction of graphene. The optimal flexural strength, Vickers hardness, indentation fracture toughness were 646.31?±?20.78?MPa, 24.64?±?0.42?GPa, 9.42?±?0.40?MPa?m^1/2, respectively, at 0.5?vol% of graphene content, which were significantly improved compared to ceramic tool material without graphene. The main toughening mechanisms originated from weak interfaces induced by graphene, and rugged fractured surface, grain refinement, graphene pull-out, crack deflection, crack bridging, micro-crack and surface peeling were responsible for the increase of fracture toughness values.     

Influence of hBN content on mechanical and tribological properties of Si3N4/BN ceramic composites

Silicon nitride materials containing 1–5 wt% of hexagonal boron nitride (micro-sized or nano-sized) were prepared by hot-isostatic pressing at 1700 °C for 3 h. Effect of hBN content on microstructure, mechanical and tribological properties has been investigated. As expected, the increase of hBN content resulted in a sharp decrease of hardness, elastic modulus and bending strength of Si₃N₄/BN composites. In addition, the fracture toughness of Si₃N₄/micro BN composites was enhanced comparing to monolithic Si₃N₄ because of toughening mechanisms in the form of crack deflection, crack branching and pullout of large BN platelets. The friction coefficient was not influenced by BN addition to Si₃N₄/BN ceramics. An improvement of wear resistance (one order of magnitude) was observed when the micro hBN powder was added to Si₃N₄ matrix. Mechanical wear (micro-failure) and humidity-driven tribochemical reaction were found as main wear mechanisms in all studied materials.     

Synergistic effects of TiB2 and graphene nanoplatelets on the mechanical and electrical properties of B4C ceramic

Monolithic B₄C, B₄C–TiB₂, and B₄C–TiB₂–graphene nanoplatelets (GNPs) were fabricated by hot pressing (HP) at 1900 °C for 1 h under an axial pressure of 30 MPa. The microstructures and mechanical and electrical properties of the B₄C composites were investigated. The results show that the GNPs are distributed homogeneously in B₄C-based ceramic composites. Compared with monolithic B₄C, the TiB₂–GNPs-containing B₄C composite exhibits an approximately 68 % increase in flexural strength and a 169 % increase in fracture toughness due to the synergistic effects of TiB₂ particles and GNPs. The toughening mechanisms mainly include TiB₂ crack deflection, crack branching, transgranular fracture and GNPs crack deflection, crack bridging, and GNPs pull-out. Additionally, the electrical conductivity of the B₄C composite reinforced with dual fillers is three orders of magnitude higher than that of monolithic B₄C due to the establishment of a conductive network. The addition of GNPs can efficiently connect the isolated conductive TiB₂ particles in the B₄C matrix and provides an additional channel for electron migration.     

Microstructure and mechanical properties of boron carbide/graphene nanoplatelets composites fabricated by hot pressing

In this study, boron carbide (B₄C)-graphene nanoplatelets (GNPs) composites, with enhanced strength and toughness, were fabricated by hot pressing at 1950 °C under a pressure of 30 MPa for 1 h. Microstructure analysis revealed that the GNPs are homogenously dispersed within the B₄C matrix. Raman spectroscopy and electron microscopy showed the orientation of the GNPs in the composites. The effects of the amount of GNPs on the microstructure and mechanical properties of the composites were also investigated. The optimal mechanical properties were achieved using 1 wt% GNPs. The relative density, Vickers hardness, flexure strength, and fracture toughness of the B₄C-GNPs composite ceramic were found to be 99.12%, 32.8 GPa, 508 MPa, and 4.66 MPa m^1/2, respectively. The main toughening mechanisms included crack deflection in three dimensions, GNPs pull-out, and crack bridging. The curled and semi-wrapped GNPs encapsulated individual B₄C grains to resist GNPs pull-out and to deflect propagating cracks.     

Effect of hBN addition on the fabrication,mechanical and tribological properties of Sialon materials

This work aims to investigate the effect of hBN on the friction and wear resistance of Sialon composite. Sialon and its composite with 10 wt% hBN were fabricated by SPS sintering. The effect of hBN additive on the phase composition, microstructure, densification behavior, mechanical and dry sliding tribological properties of Sialon material was studied. Being sintered at 1600 °C for 10 min, compared to monolithic Sialon, Sialon-hBN composite has more refined β-Sialon grains with smaller aspect ratios and slightly declined relative density. The hardness of the Sialon-hBN composite was reduced due to the weak bonding between Sialon and hBN grains. Nevertheless, its fracture toughness increased ascribing to the toughening mechanisms, including crack deflection and crack bridging. hBN had an essential impact on the tribological performances of the composite due to its lower friction coefficient and good lubrication action. Under the same densification level (i.e., with a relative density of around 97.5%), the friction and wear resistance of Sialon-hBN composite were much better than monolithic Sialon. The main wear mechanisms were tribolayer formation, oxidized wear, and abrasive wear.     

Effects of nano-ZrO2 content on microstructure and mechanical properties of GNPs/nano-ZrO2 reinforced Al2O3/Ti(C,N) composite ceramics

Dense Al₂O₃/Ti(C,N) composite ceramics reinforced with GNPs/nano-ZrO₂ were fabricated by hot-press sintering. The effects of nano-ZrO₂ content on the microstructure and mechanical properties of the prepared Al₂O₃/Ti(C,N)/GNPs/ZrO₂ composites were investigated. Results showed that nano-ZrO₂ inclusions refined the matrix grains significantly and resulted in the formation of intra-granular structure. Excellent comprehensive mechanical properties were achieved via addition of combined GNPs and nano-ZrO₂. In particular, the fracture toughness of composites incorporating GNPs (0.4 wt%)/ZrO₂ (1 wt%) exceeded 11 MPa m^1/2, which was increased by more than 86 % compared with that of Al₂O₃/Ti(C,N) ceramic composites without GNPs/ZrO₂. The main toughening mechanisms have been identified as stress-induced phase transformation, crack bridging, deflection and pull-out of GNPs. The toughening effects originated from GNPs were enhanced with the introduction of nano-ZrO₂ because of not only the residual stress resulted from phase transformation but also the formation of intra-granular structure with uneven surface around GNPs.     

High-temperature stability of microstructure and mechanical properties of eutectic-reinforced high-entropy ceramic joint

(HfTaZrNbTi)C₅ high-entropy ceramic (HEC) brazed joint was obtained with TiNi-Nb alloy and the brazing seam was primarily filled by TiNi + Nb eutectic microstructure. The highest shear strength of the joint obtained under the condition of 1220 °C/10 min reached 167 MPa and 137 MPa at room temperature and 800 °C, respectively. Moreover, the high-temperature stability of the brazed joint was investigated by air oxidation testing at 800 °C. Compared to the HEC, the TiNi + Nb eutectic microstructure in the brazing seam exhibited superior oxidation resistance. After oxidation for four hours, the joint shear strength still maintained 100 MPa, while it was reduced to 22 MPa after oxidation for eight hours due to the dramatic damage of the HEC. The results showed that the brazed HEC joint possessed high shear strength at an elevated temperature of 800 °C for four hours although the high-temperature endurance of the joint was weak.     

Microstructure and mechanical properties of B4C matrix composites prepared via hot-pressing sintering with Pr6O11 as additive

High-performance B₄C-PrB₆ composites were prepared via hot-pressing sintering with matrix phase B₄C and with 2–5 wt% Pr₆O₁₁ as additive. The effects of different sintering processes and Pr₆O₁₁ content on the microstructure and mechanical properties of the composites were studied in detail. It is found that increasing sintering temperature and pressure will contribute to the densification of B₄C-PrB₆ composites. Coarse grains are formed in B₄C without additives at high temperature conditions, resulting in the decrease of the densification. Pr₆O₁₁ can effectively hinder the formation of coarse grains and finally promote the densification of the composites. The main toughening mechanisms of composites was crack deflection. The composites with 4 wt% Pr₆O₁₁ prepared at 2050 °C and 25 MPa had the best comprehensive mechanical properties. The relative density, hardness, flexural strength and fracture toughness reached to 98.9%, 37.6 GPa, 339 MPa and 4.4 MP am^1/2, respectively.     

Effect of Y2O3-stabilized ZrO2 whiskers on the microstructure,mechanical and wear resistance properties of Al2O3 based ceramic composites

The aim of this study was to improve the mechanical properties of Al₂O₃ ceramics by the addition of Y₂O₃-stabilized ZrO₂ whiskers (designated as Al₂O₃/YSZ_W composite) through the flux method and hot-pressing technology. The effect of YSZ_W content on their microstructure, phase composition and transformability, mechanical properties, and wear resistance was systematically investigated. The Al₂O₃/YSZ_W composites containing 10 wt% YSZ_W exhibited the best mechanical performance, including the highest content of YSZ_W tetragonal phase and transformability as well as the largest values in their relative density (99.5%), hardness (1969 HV), fracture toughness (9.57 MPa m^1/2) and flexural strength (855 MPa). The strengthening and toughening of the Al₂O₃/YSZ_W composites were attributed to the YSZ_W tetragonal-monoclinic phase transformation as well as the whiskers reinforcing effect. Furthermore, the Al₂O₃/YSZ_W composites also showed the highest friction and wearing properties.     

Microstructure and properties of a graphene platelets toughened boron carbide composite ceramic by spark plasma sintering

A kind of B₄C/SiC composite ceramic toughened by graphene platelets and Al was fabricated by spark plasma sintering. The effects of graphene platelets and Al on densification, microstructure and mechanical properties were studied. The sintering temperature was decreased about 125–300?°C with the addition of 3–10?wt% Al. Al can also improve fracture toughness but decrease hardness. The B₄C/SiC composite ceramic with 3?wt%Al and 1.5?wt% graphene platelets sintered at 1825?°C for 5?min had the optimal performances. It was fully densified, and the Vickers hardness and fracture toughness were 30.09?±?0.39?GPa and 5.88?±?0.49?MPa?m^1/2, respectively. The fracture toughness was 25.6% higher than that of the composite without graphene platelets. The toughening mechanism of graphene platelets was also studied. Pulling-out of graphene platelets, crack deflection, bridging and branching contributed to the toughness enhancement of the B₄C-based ceramic.     

Effects of HfC addition on microstructures and mechanical properties of TiC0.7N0.3-based and TiC0.5N0.5-based ceramic tool materials

Effects of HfC addition on microstructures and mechanical properties of TiC_0.7N_0.3-based and TiC_0.5N_0.5-based ceramic tool materials were investigated. The results showed that the same by-products such as HfN_0.4, HfNi, Ti_0.76Hf_0.24Ni, TiNi_0.85Co_0.15 and HfCo₆ were discovered in these ceramics. To some extent, HfC additive can inhibit their denitrification in the sintering process. The HfC particles can produce the crack flection and a suitable HfC content can improve mechanical properties of these ceramics effectively. Besides, the TiC_0.5N_0.5-HfC ceramics exhibited a poor sinterability compared to TiC_0.7N_0.3-HfC ceramics, showing much more pores in fracture and polished surfaces micrographs; grains in TiC_0.7N_0.3-HfC ceramics are finer than that in TiC_0.5N_0.5-HfC ceramics; the HfC particles dispersion in TiC_0.7N_0.3-HfC ceramics is more uniform than that in TiC_0.5N_0.5-HfC ceramics; thus, the mechanical properties of TiC_0.7N_0.3-HfC ceramics are superior to that of TiC_0.5N_0.5-HfC ceramics. In addition, their fracture mechanism is a combination of transgranular fracture and intergranular fracture. As a consequence, the enhancement of their mechanical properties is conducive to the presence of intermetallic compounds, the fine microstructure and the suitable HfC content.     

Microstructure and mechanical properties of boron nitride nanosheets-reinforced fused silica composites

In order to overcome intrinsic brittleness and poor mechanical properties of fused silica (FS), boron nitride nanosheets (BNNSs) as a novel reinforcement were employed for fabrication of BNNSs/fused silica composites. BNNSs with micron lateral size were homogeneously dispersed with FS powder using a surfactant-free flocculation method and then consolidated by hot pressing. The flexural strength and fracture toughness of the composite with the addition of only 0.5 wt.% BNNSs increased by 53% and 32%, respectively, compared with those of pure FS. However, for higher BNNSs contents the improvement in mechanical properties was limited. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out, crack bridging, and crack deflection mechanisms.     

Role of non-functionalized oxide nanoparticles on mechanical properties and toughening mechanisms of epoxy nanocomposites

Over the past few decades, the use of epoxy resins has gained significant attention from worldwide researchers due to its advantages in structural applications in various sectors like automotive, construction, and aerospace industries. This article summarizes and reviews the research on mechanical properties and toughening mechanism of epoxy composites filled with non-functionalized oxide nanoparticles. The incorporation of nanomaterials into the polymer matrix has been considered to be the most effective route to improve the mechanical properties of polymer composites. But the inherent brittle nature and cross-linking ability of epoxy makes it vulnerable to crack initiation and crack growth and limits its use in advanced structural applications. Recently, various kinds of nanofillers such as carbon nanotubes (CNTs), organic and inorganic oxide nanoparticles have attracted industrial interest due to their excellent mechanical, thermal, and electrical properties which can provide a dramatic improvement in the properties of epoxy composites but their dispersion issue, agglomeration and bundling problems deteriorate several important mechanical parameters of the epoxy composites. To date, no review article focused on the role of non-functionalized oxide nanoparticles on the improvement in mechanical properties of the reinforced epoxy composites. This review article assesses and summarizes some most recent findings on the de-agglomeration process, mechanical properties, and toughening mechanisms of epoxy nanocomposites reinforced with four types of most preferred non-functionalized oxide nanoparticles such as Al₂O₃, TiO₂, SiO_2, and ZrO₂.     

Effect of boron nitride nanosheets addition on the mechanical and dielectric properties of magnesium oxide ceramics

Boron nitride nanosheets (BNNSs)/magnesium oxide (MgO) composites were prepared via hot pressing. Mechanical properties of MgO ceramics were improved obviously in virtue of adding BNNSs. The bending strength of the 1 wt% BNNSs/MgO composite increased by about 85% than that of the monolithic MgO. The fracture toughness increased by 34% with the addition of 1.5 wt% BNNSs. Microstructural analyzes have shown that the toughening mechanisms are combinations of the pull-out and bridging of BNNSs, crack deflection, and crack bypassing mechanisms. The addition of a small amount of BNNSs don't destroy the excellent dielectric properties of composites. The dielectric constant of the sample doped with 1 wt% BNNSs was about 9.5 in the whole X-band and the vast majority of P-band, and the loss tangent was less than 5 × 10⁻³ in 10–15.8 GHz.     

Design and mechanical properties of particle-reinforced polymer-matrix functionally graded materials applied on elastic polishing pad

Aiming at the functionally graded materials (FGMs) formed by mixing the abrasive particles and rubber with different kinds and mass ratios, the numerical analysis and experimental verification of its mechanical properties were carried out. The FGMs was applied on the elastic polishing pad for obtaining ultra-smooth surfaces of hard and brittle materials, such as glass ceramics and silicon wafers. Its structure and properties changed in the radial direction quasi-continuously. Regarding to the design of the FGMs, the maximum standard deviation of Young's modulus was 1.09 after 6 repeated tests, when the SiC abrasive particles and chloroprene rubber (CR) were mixed with mass ratio less than 50 phr. Furthermore, there are three types of mechanical properties, named edge stress, boundary stress and central stress, when the workpiece was applied to the elastic polishing pad mainly made of the FGMs mentioned above. If using matching module method, the abrupt phenomenon of edge stress was basically eliminated. Increasing the gradient rings could reduce the abrupt change of boundary stress, and the contact stress in the single gradient ring was basically kept constant when the FGMs was up to 8 gradient distribution. Meanwhile, due to the viscoelastic property of rubber, there was a difference of 25% between the dynamic and static stress values of the elastic polishing pad with acrylate rubber (ACM) as the matrix, and the maximum difference was less than 4.7% when using CR as the matrix. Besides, the dynamic mechanical analysis (DMA) showed that the loss factor tanδ was less than 0.1 in the processing temperature range of 20 °C–50 °C. Therefore, the FGMs with SiC or Al₂O₃ as particle-reinforcement, and CR as polymer-matrix could largely solve the inconsistent problem of central stress under dynamic and static conditions.     

Enhanced toughness and strength of boron carbide ceramics with reduced graphene oxide fabricated by hot pressing

Boron carbide (B₄C) hybrids with different contents of graphene oxide (GO) were prepared by a heterogeneous co-precipitation method using cetyltrimethyl ammonium bromide (CTAB) as the cationic surfactant. The as-obtained mixtures were further hot-pressed at 1950 °C for 60 min under 30 MPa, by which B₄C–reduced GO (rGO) composites were fabricated. It was found that the addition of only 0.5 wt% rGO could alter the predominance of trans-granular fracture in monolithic B₄C ceramic material to mixed trans-granular and inter-granular modes in B₄C–rGO composites. The flexural strength and fracture toughness of the B₄C–2 wt% rGO were increased by 31% (from 350 to 455 MPa) and 83% (from 3.20 to 5.85 MPa·m^1/2), respectively, compared with those of pure B₄C. The improved mechanical properties are attributed to the mechanisms of pull-out and bridging of rGO and crack deflection, as evidenced by microstructural observations. The energy dissipation in the present B₄C–rGO composites was further verified using two micromechanical models.     

Enhanced mechanical properties of porcelain ceramic tile/Kevlar fabric composite with bio-inspired shell-like structure

Ceramic materials with high strength, toughness, and excellent impact resistance are urgently required for many structural applications, but these mechanical properties are difficult to achieve in traditional ceramic tiles due to their inherent brittleness. Inspired by the specific structure of shells, the multilayered ceramic tile/Kevlar fabric composite with a bio-inspired shell structure was successfully fabricated via a surface hydroxylation followed by simple hot press process. It is found that the composites have representative step-like fracture behaviors rather than brittle fracture, which has been proven to possess a better ability of mechanical performance and noncatastrophic failure behavior compared to same-thickness ceramic tile. Specifically, the bending strength, fracture toughness, and fracture work of the composite with a 15-tier structure come to 836.5 ± 12.5 MPa, 14.6 ± .2 MPa·m^1/2, and 7228.8 ± 108.4 J·m^1/2, which are even better than those of reported advanced materials. Such fracture-resistant behaviors are correspondent to the strengthening effects of the crack deflection, interfacial debonding, and fiber pull out, accompanied by bio-inspired structure and appropriate bonding state between brittle or ductile layers. This resin or fabric content can be used as well as the slip systems to transfer the internal stress in time to consume more fracture energy per unit length and prevent risky brittle fracture, while carrying loads. We expect these findings to provide vital guidance for promoting the applications of traditional ceramics in bio-inspired high-performance composites for actual ceramic manufacturers.     

Investigation of the structure and mechanical properties of a novel dental graded glass/zirconia ceramic

Constructing graded structure is a promising solution to reduce the occurrence of cracking and delamination of bilayered zirconia prosthesis. In this work, a novel graded glass/zirconia ceramic was developed by utilizing the interdiffusion between dense zirconia and a novel lithium disilicate glass in the SiO₂-Li₂O-Al₂O₃ system. Results demonstrated that a graded glass/zirconia structure with a depth of about 300 µm was constructed, which exhibited obviously gradient characteristics in microstructure, glass content and mechanical properties. The hardness (H) and elastic modulus (EM) values at the surface reduced significantly (64% for H and 79% for EM), and increased gradually with depth of graded layer. When the graded layer was subjected to loading force, the biaxial flexural strength increased. The mechanism of the evolution of graded structure and change of strength were also elucidated in detail. This study provides a promising strategy to improve the interface stability of bilayered zirconia restoration.     

Mechanism of improving the mechanical properties of Si3N4/TiC ceramic tool materials prepared by spark plasma sintering

Spark plasma sintering (SPS) is a new sintering method having shorter sintering time and higher densification speed than the traditional sintering methods. In this paper, the Si₃N₄/TiC ceramic tool material is sintered by SPS. The microstructure and mechanical properties of the material under different sintering parameters are compared. The sintering process of the material is then analyzed, and the best sintering parameters are obtained. Heat the material to 1600°C and keep the temperature for 15 min, then continue to heat to 1700°C and keep the temperature for 10 min, Si₃N₄/TiC ceramic tool material has high mechanical properties, its bending strength, fracture toughness, and Vickers hardness are 959 MPa, 8.61 MPa·m^1/2, and 15.21 GPa, respectively. The scanning electron microscope (SEM) analysis shows that under this condition, the sintering additives and Si₃N₄/TiC material form the liquid phase, which makes the Si₃N₄ particles rearrange, dissolve, precipitate, and transform into rod shape β-Si₃N₄. In addition, under the action of pulse current and external pressure, electric sparks are generated between TiC particles, which allows the material transfer and particle refinement. Therefore, the β-Si₃N₄ has uniform grain size, and it is vertically and horizontally arranged in the structure, which makes the material have excellent mechanical properties.