Higher Fracture Toughness Values Research Articles

Evaluation of the Mechanical Properties and Fatigue Resistance of the ZrO2CeYAl2O3 Composite

This work aimed to evaluate the fatigue limit of the zirconia ceramic composite stabilized with yttria and ceria reinforced with alumina platelets (ZrO2CeYAl2O3) and characterize the mechanical properties of sintered specimens. Bar-shaped specimens were compacted by uniaxial pressing in a rigid die and sintered at 1500 °C-2 h. Subsequent characterizations included quantitative phase analysis by X-ray diffractometry, determination of density, modulus of elasticity, microhardness, fracture toughness, four-point flexural strength, and fatigue limit. Observations of fracture mechanisms were carried out using confocal and scanning electron microscopy (SEM). The sintered samples presented values above 98% of relative density. Complex microstructures with equiaxed, homogeneously distributed submicrometer grains and planar alumina platelets were observed by SEM. The composite samples showed high values of fracture toughness due to the transformation, during the test, from the tetragonal to monoclinic phase, causing an increase in volume and creating compression zones around the crack, making it difficult to propagate. The average flexural strength reached 445.55 MPa, with a Weibull modulus (m = 16.8), revealing low flexural rupture stress data dispersion. In the composite evaluated in this work, the occurrence of the tetragonal → monoclinic transformation that occurs in the Ce-TZP present at the triple points and grain boundaries during cyclic loading produces “crack tip shielding”, that is, a restricted elastic zone (zone shielding) that surrounds the crack tip. This phenomenon leads to a reduction in the stress intensity factor at the tip of the crack and slows down its growth, generating an increase in the fatigue resistance of the composite.

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.

Properties of a Pressureless Sintered 2Y-TZP Material Combining High Strength and Toughness

Yttria stabilized zirconia materials are frequently used in mechanical engineering and biomedical applications. Demanding loading conditions require materials combining a high level of strength and fracture toughness. A ready-to-press alumina doped 2 mol% yttria-stabilized zirconia powder was shaped by axial pressing and sintering in air at 1250–1500 °C for 2 h. At 1350 °C the best combination of strength (1450 MPa) and toughness (7.8 MPa√m) was achieved. Materials sintered in the middle of the chosen temperature range combine full density, high transformability and small grain size. Toughness measurements by direct crack length measurements delivered unrealistically high fracture toughness values.

Tough and Ductile Architected Nacre‐Like Cementitious Composites

AbstractEnhancing fracture toughness and ductility of brittle materials such as concrete remains a challenge. Nature offers numerous mechanisms to enhance fracture toughness using purposeful designs of materials’ architecture. Natural nacre exhibits high fracture toughness by promoting inelastic deformation and hierarchical toughening mechanisms. Here, “nacre‐like‐separated” and “nacre‐like‐grooved” cementitious composites inspired by brick‐and‐mortar arrangement of mollusk shells are proposed. These nacre‐like composites are engineered by laser processing cement paste into individual tablets and grooved patterns (as intentional defects) and laminating them with limited amounts of suitable elastomeric (polyvinyl siloxane) interlayers. It is found that interlayer deformation, tortuous crack propagation guided by the defects, and crack bridging are the main toughening mechanisms in these composites that lead to rising resistance curves. The study hypothesizes tablet sliding as an additional toughening mechanism in “nacre‐like‐separated”, preventing tablet failure and leading to the postponed onset of bulk composite failure. These mechanisms significantly enhance both fracture toughness and ductility by 17.1 and 19 folds, compared to constituent hardened cement paste, respectively. By engineering laser‐induced defects into tabulated cementitious‐elastomeric material at meso‐scale, a class of tough and ductile cementitious composites is introduced, resulting in significantly high fracture toughness values (73.68 MPa.mm1/2), comparable to Ultra‐high‐performance‐concrete without sacrificing the strength.

Development and characterization of Al2O3/SrAl12O19 reinforced zirconia with high fracture toughness and low-temperature degradation-resistant for dental applications

The low fracture toughness and sensitivity to low-temperature degradation (LTD) are the primary reasons for the suboptimal long-term performance of dental zirconia. Composite ceramics of zirconia have gained popularity due to their ability to combine the benefits of various reinforcements. In this study, Al2O3–SrAl12O19–3Y/4Y/5Y–ZrO2 composite ceramics were fabricated using the Pechini method, and the optimal sintering temperature and time were investigated. The relative density, microstructure, grain size, mechanical properties, and LTD resistance of the samples were characterized. The results indicated that the composite achieved optimal performance when sintered at 1500 °C for 3 h. Al2O3 and SrAl12O19 primarily influence the properties of the zirconia composite ceramics by modulating their density and grain size. With an increase in the content of Al2O3 and SrAl12O19, the relative density first increases and then decreases, while the grain size exhibits an inverse trend, resulting in an initial increase followed by a decrease in fracture toughness. Additionally, the rate of increase in the m-phase fraction of the zirconia composite slowed down, but it reached a similar level after 64 h of LTD. The incorporation of 8 vol% Al2O3 and 8 vol% SrAl12O19 into 3Y–ZrO2 resulted in a ceramic composite with the highest fracture toughness values and acceptable LTD sensitivity, measured at 5.23 ± 0.25 MPa m1/2 and 48.35 ± 5.70% m-phase (LTD 64 h), respectively. This composite also exhibited high bending strength (990.09 MPa) and hardness (16.52 GPa), making it a promising alternative to conventional 3Y-TZP ceramics commonly used in dentistry.

On the effects of B4C addition on the microstructure, mechanical properties, wear and thermal stability of TiCN- Co -Cr3C2-Si3N4 cermets developed by vacuum hot pressing

This paper reports the development of TiCN - Co - Cr3C2 - Si3N4 cermets modified with the addition of B4C. Cermets of three different compositions with varying B4C in TiCN - Co - Cr3C2 - Si3N4 were fabricated. The TiCN, Co, Cr3C2, Si3N4 and B4C powders in the combinations 80%TiCN-5%Co-5%Cr3C2–5%Si3N4–5%B4C; 75%TiCN-5%Co-5%Cr3C2–5%Si3N4–10%B4C; 70%TiCN-5%Co-5%Cr3C2–5%Si3N4–15%B4C were ground in a ball milling unit for six hours at a speed of 300 rpm at a ball-to-powder ratio of 10:1. The powders were then sintered in a vacuum hot press at a temperature of 1600 °C and a pressure of 50 MPa with soaking time of 90 min. For comparison purpose, 90%TiCN-5%Co-5%Cr3C2 cermet was prepared. The microstructure of the sintered cermets revealed the core-rim structure. The Vickers hardness test was done with a load of 10 Kg and for duration of 10 s. Fracture toughness was measured using the crack length data obtained from the hardness test using scanning electron microscopy. The cermet with a composition 75% TiCN-5%Co-5% Cr3C2–5% Si3N4–10% B4C produced higher hardness of 26.53 ± 0.56 GPa and fracture toughness of 10.29 ± 0.18 MPam and 70% TiCN-5%Co-5% Cr3C2–5% Si3N4–15% B4C showed high fracture toughness value of 11.23 ± 0.09 MPam with hardness value of 21.05 ± 0.10 GPa. The cermet composition 75% TiCN-5%Co-5% Cr3C2–5% Si3N4–10% B4C retained the hardness of 16.85 GPa even after annealing at 600 °C. The sintered cermets tend to form TiO2 which determines the hardness of the annealed cermets at a range of 600 °C – 1000 °C. The presence of these oxides tends to decrease the hardness. The wear test was performed taking the cermet as the pin material. The abrasive and adhesive wear mechanisms were dominant in the cermets. The harder precipitates formed tend to increase wear resistance by reducing the wear rate. The harder precipitates (TiN and TiB2) formed mainly due to the addition of Si3N4 and B4C, this addition promotes adhesive wear by a tribolayer formation.

Zirconia‐containing glass‐ceramics: From nucleating agent to primary crystalline phase

AbstractThis article reviews promising studies on the design, manufacturing, microstructure, properties, and applications of glass‐ceramics containing ZrO2 and relevant glass‐ceramic matrix composites. After the addition of ZrO2 to a glass‐ceramic composition, it can persist in the residual glassy phase, facilitate nucleation, and/or precipitate as ZrO2 or another zirconate crystalline phase. Also, ZrO2‐reinforced or ZrO2‐toughened glass‐ceramics can be designed as composites. In this article, the term “ZrO2‐containing glass‐ceramics” encompasses all these scenarios in which ZrO2 is present. Such glass‐ceramics offer a wide range of applications in modern industries, including but not limited to architecture, optics, dentistry, medicine, and energy. Since S. Donald Stookey's discovery of glass‐ceramics in the early 1950s, the most important scientific efforts reported in the literature are reviewed. ZrO2 is commonly added to glass‐ceramics to promote nucleation. As a result, the role of ZrO2 in structural modification of residual glass and stimulating the nucleation in glass‐ceramic is first discussed. ZrO2 can also be designed into the main crystalline phase of glass‐ceramics, contributing achieving super high fracture toughness above 4 MPa·m0.5. Experimental and computational studies are reviewed in detail to elucidate how the transformation toughening and other mechanisms help to achieve such high values of fracture toughness. Sintered and glass‐ceramic matrix composites also show promise, where ZrO2 contributes to improved stability and mechanical properties. Finally, we hope this article will provoke interest in glass‐ceramic materials in both the scientific and industrial communities so that their tremendous technological potential in developing, for example, tough, thermally stable, transparent, and biologically compatible materials can be realized more widely.

The role of carbon addition on properties of boron carbide- silicon carbide composites

In this research, composites were produced by mixing boron carbide (B4C) and silicon carbide (SiC) with varying amounts of carbon (C) and densifying them via spark plasma sintering at 1950 °C for 5 min. The effects of different C contents on the properties of the composites were observed. Density, elastic modulus, microstructure, Vickers hardness, and fracture toughness were evaluated. It has been observed that the oxygen content of starting powders should be matched with the added C content to obtain high density and desirable mechanical properties. The highest density, elastic modulus, and hardness values were obtained in samples containing 1.5 wt% C. The highest elastic modulus was obtained in the 10 wt% B4C–SiC-1.5 wt% C sample, at 451 GPa. The highest hardness value was 32.85 GPa, corresponding to the sample containing 90 wt% B4C–SiC-1.5 wt% C. The highest fracture toughness value was attained by the sample containing 10 wt% B4C–SiC-2.5 wt% C, at 2.87 MPa m1/2. Lastly, the composite samples showed transgranular fracture behavior.

Comparative analysis of self-cure and dual cure-dental composites on their physico-mechanical behaviour.

Clinical practitioners may have become familiar with the rapid transformation of dental composites. However, they may not scientifically understand the factors influencing the mechanical and physical properties. Scientific knowledge of filler-resin interaction can significantly improve clinical understanding of resin composites. Several independent studies have examined the mechanical and physico-mechanical properties of dental resin composites; however, no comprehensive study has examined the influence of fillers and resin materials on the physico-mechanical properties of both self-cure and dual-cure composites. This study performed investigations on the physico-mechanical behaviour of four commercially available dual-cure dental composites (Bioactive, Fill Up!, Surefil One, Cention N) and two commercially available self-cure dental composites (Stela Capsule and Stela Automix). Test specimens for flexural and compressive strength, microhardness, fracture toughness, and hydrolytic behaviour were prepared and tested as per respective standards. The data sets were statistically analysed using one-way ANOVA and Tukey's post-hoc comparison. There was a substantial variation in flexural strength and modulus values in this study, ranging from 32.0 to 113.4 MPa and 2.36 to 12.07 GPa, respectively. Similarly, there were significant differences in compressive strength between the materials in this study, ranging from 119.3 to 223.5 MPa. The highest fracture toughness value was found to be 1.41 MPa.m0.5, while the lowest value was 0.43 MPa.m0.5. Variations in surface microhardness were significant (24.11-68.0 N/mm2), which correlated with the filler content. Water sorption and solubility demonstrated high variations among materials, with Surefil One exceeding ISO 4049 thresholds significantly. A linear correlation can be established between surface microhardness (HV) and flexural and compressive moduli, as well as filler content (wt.%). However, both flexural and compressive strengths are impacted by the resin's constituent monomers and the resin-filler matrix's cross-linking capability. Additionally, factors such as filler size, shape, and the cross-linking ability of the resin-filler matrix play a crucial role in fracture toughness and the propagation of cracks within the restoration. Also, resin monomers and filler particle size affect the hydrolytic degradation characteristics of composites, which can also affect their mechanical properties. © 2023 Australian Dental Association.

Comparative study of two bioactive dental materials

ObjectivesNew bioactive materials were introduced to not only restore the lost dental hard tissue but also to release fluoride that inhibits demineralization and occurrence of secondary caries. The current study thus aims to assess Fluoride release as well as the mechanical and physical properties of two new commercially available bioactive restorative materials. MethodsTwo materials, Cention® Forte (CF) (Ivoclar Vivadent), Surefil one™ (SO) (Denstply Sirona), were evaluated in terms of fracture toughness (FT), flexural strength (FS), flexural modulus (FM) (ISO 4049), compressive strength (CS), and Vickers hardness (VH). In addition, thermogravimetric analysis (TGA) was performed, as well as pH measurements and quantification of Fluoride release after immersion in distilled water at times of 0, 7, 14 and 21 days. The sealing ability was evaluated using silver nitrate dye penetration on natural teeth. Finally, Energy-Dispersive X-Ray Spectroscopy (EDX) was used to investigate the surface composition of the two studied material surfaces. The data were statistically analyzed using Independent T-Tests; the chosen significance level was α = 0.05. ResultsCF had significantly higher FT values compared to SO (p = 0.001). Also the FS results showed that CF had significantly higher values (90.11 MPa), followed by SO (22.15 MPa). The CS values showed the same order with significantly higher values for CF (231.79 MPa). While the FM and VH showed the reverse order with SO having significantly higher values than CF. pH measurements showed that CF evolved towards significantly higher pH values after 3 weeks in distilled water, while thermal properties showed more stability and higher resistance to degradation for CF compared to SO. The silver nitrate penetration results showed significantly better sealing ability for CF compared to the self-adhesive SO. Finally, EDX surface analysis results were consistent with the release profiles and confirmed the composition of the two tested materials. SignificanceBoth materials, demonstrated enhanced Fluoride release ability, and hence good remineralisation potential in vitro that could prevent recurrent carious lesions in vivo. The composition based on acrylic polymerization showed better mechanical resistance to bending and fracture, and higher sealing ability than those based on acid base reaction.

Effects of SiC nanowires and whiskers on high‐entropy carbide‐based composites sintered at low and high temperatures

AbstractThis study aimed to investigate the toughening effects of SiC nanowires (SiCnw) and SiC whiskers (SiCw) on high‐entropy carbide based composites prepared at different temperatures (1600°C and 2000°C). At low temperature (1600°C), SiCnw and SiCw maintain their original morphology and properties, and exhibit the good toughening effects. The SiCnw with larger aspect ratio and more curly wires exhibit a much stronger toughening effect on the (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites reinforced with 15 vol.% SiCnw, which shows the highest value of fracture toughness about 6.7 MPa∙m1/2. However, at high sintering temperature (2000°C), SiCnw and SiCw are prone to thermal‐induced damages, which significantly reduces their mechanical properties, and thus, toughening effects on (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites. The addition of SiCw, which have better thermal stability at 2000°C, results in the (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8–15 vol.% SiCw composite exhibiting relatively better fracture toughness, about 3.7 MPa∙m1/2. Based on the results of the current study, the critical influence of SiCnw and SiCw on the toughening of (Ti0.2Zr0.2Nb0.2Ta0.2Mo0.2)C0.8 composites is highly dependent on their high‐temperature thermal stability.

Synthesis of B<sub>4</sub>C–TiB<sub>2</sub> composition powder mixtures by carbidobor reduction using nanofibrous carbon for ceramic fabrication

The results of the researching process of obtaining composition powder material B4C–TiB2 by carbide reduction of titanium dioxide, using carbon reducing agent – carbon nanofibers, are presented. Furthermore, the results of studying of some properties of ceramics made using the synthesized powder are presented. The synthesis of composite materials was carried out in an induction crucible furnace for 20 min in the temperature range of 1200–1900 °C in an argon atmosphere. It has been established that the optimum temperature of the synthesis is 1650 °C, irrespective of the batch composition. The characteristics of the composite powders containing 10–30 mol. % of the TiB2 phase have been studied. X-ray electron microscopy has revealed that the particles of the powder are predominantly aggregated. There are two peaks in the particle size distribution histograms. The part of the histogram with a smaller particle size mainly characterizes the B4C phase. The part of the histogram with a larger particle size characterizes the TiB2 phase. The average particle size of the B4C phase is in the range of 5.3–5.5 µm, and that of the TiB2 phase is in the range of 33.6–41.9 µm. The average size of 50 % of composite powder’s particles for these contents does not exceed 13.4 μm. The surface area of the samples does not exceed 5 m2/g. The oxidation of the composite powder materials by atmospheric oxygen begins at a temperature of approximately 500 °C. At the same time, when the temperature reaches 1000 °C, no more than 45 wt. % of the studied powders is oxidized. Ceramics made with the synthesized powder mixture B4C + 30 mol. % TiB2 by hot pressing has shown rather high values of relative density (99.0±1.1 %) and fracture toughness (5.0±0.2 MPa∙m0.5).

Unsaturated polyester fracture toughness mechanism with blending to vinyl ester and MMA

In this research, a method was used to increase the brittleness of unsaturated polyester polymer by mixing it with vinyl ester. The choice of vinyl ester to increase the toughness of this polyester is because it is easy to form and this material has wide applications in engineering. However, this polyester has several weaknesses, namely, it is very stiff, brittle, and unable to withstand cracking loads and breaks easily due to impact. Polyester has a rigid nature because this material has cross-chain links of material that are tightly locked and interconnected with each other. With the addition of this vinyl ester, this tightly connected rigid chain is disrupted by the vinyl ester chain, thereby increasing the toughness of the polyester. Steps were taken to increase the crack resistance of unsaturated polyesters with the addition of vinyl esters, starting with the percentages of 10%, 20%, 30%, and 40% and comparing them with pure polyester. The results obtained showed that the crack resistance of polyester increased with the addition of 40% wt vinyl ester. The results show that the highest fracture toughness value is indicated by the value of the stress intensity factor of K1c=1.752 MPa.m0.5.

Translucent and Highly Toughened Zirconia Suitable for Dental Restorations

Background: There is a limit to improving the characteristics of zirconia with only one kind of stabilizing element such as yttrium. The purpose of this study is to systematically evaluate the effects of various co-doped elements on mechanical and optical properties and to develop a novel composition of zirconia with enough properties to apply to dental restorations. Methods: Forty-four kinds of zirconia were prepared by combining trivalent cations yttrium (Y) and ytterbium (Yb), and pentavalent cations niobium (Nb) and tantalum (Ta) oxide as stabilizers. The combined contents ranged from 0 to 5.6 mol% for Y2O3, 0 to 4.2 mol% for Yb2O3, 0 to 1.5 mol% for Nb2O5, and 0 and 1.2 mol% for Ta2O5. These specimens were determined for fracture toughness and opacity. X-ray diffraction studies were undertaken to evaluate the microstructural change. Results: The present study revealed that adding of the trivalent cations Y and Yb reduced fracture toughness and opacity, whereas the addition of pentavalent cations Nb and Ta to zirconia stabilized with trivalent cations increased both properties. There was no clear difference in the effects of Y and Yb, Nb, and Ta. Conclusions: Considering many factors, the following composition is optimal: 3–4.2 mol% Y2O3 and/or Yb2O3 stabilized zirconia with up to 1.5 mol% Nb2O5 has sufficiently high fracture toughness values and sufficiently high translucency suitable for dental restorations.

Evaluation of the fracture toughness of butt-welded joints using the boundary effect model

Yielding loads (Py) from small three-point-bending (3-p-b) specimens with notch tips in the heat-affected zone, fusion zone, weld metal, and base metal of Q235 (common carbon steel in China) were used to estimate the corresponding fracture toughnesses. To model the elastic and plastic fracture around the Q235 welded joint, the boundary effect model initially developed for quasi-brittle fracture of heterogeneous solids with a large crack-tip fracture process zone was adopted in this study, bypassing the stringent ASTM standard requirements on the specimen size, initial crack length, and un-notched ligament. It was found that the weld metal had the highest fracture toughness value around 130 MPa√m, followed by the heat-affected zone of 109 MPa√m, the base metal of 83 MPa√m, and the fusion zone of 77 MPa√m. Microstructures and notch-tip plastic zones in each section of the welded joint were measured and used to explain the fracture toughness measurements.

Effect of laser energy density on microstructure, wear resistance, and fracture toughness of laser cladded Mo2FeB2 coating

To expand the applications of Mo2FeB2 ternary borides in industry, laser cladding technology was utilized to prepare Mo2FeB2 coating to improve the properties of the AISI 1045 medium steel substrate. The influence of cladding laser energy density (75–175 J⋅mm−2) on the obtained coating properties was studied, such as geometric characteristics, microstructure, microhardness, wear resistance, and fracture toughness. It can be found from the results that width and dilution rate increased with the increase of laser energy density when the coating had the same scanning speed or laser power, while the wetting angle had an opposite result. The ability of Marangoni convection was increased with the increase of laser energy density, and the hard phase particles became coarse and formed needle-like structures and herringbone structures. An excellent bonding zone was formed between the coating and the substrate. The direction of crystal structures in the bonding zone grew along the direction of heat dissipation. Based on the results of the mechanical properties of the coating, it can be concluded that the coating fabricated with 90 J⋅mm−2 laser energy density had the highest microhardness (1283.7 HV0.5) and excellent wear resistance (0.34 coefficient of friction, 2.9 mg wear mass loss). The wear forms were typical abrasive and adhesive wear, where a smooth worn surface was formed, and only pits or shallow grooves existed. The coating obtained with the highest laser energy density (175 J⋅mm−2) had a high fracture toughness value (16.73 MPa⋅m1/2). Besides, the coatings had typical transgranular fractures with different laser energy densities. Hence, a coating with perfect properties can be fabricated by adjusting laser cladding parameters.

MODERN TECHNOLOGIES FOR THE MANUFACTURE OF GLASS-CERAMIC DENTAL PROSTHESES

The relevance of the problem of improving the quality of life and protecting human health in the context of the successful development of the modern society was presented. A literary review of well-known modern technologies for the design and manufacture of dental prostheses was carried out, as well as the leading domestic and foreign companies that were engaged in this were given. The history of the development of materials for obtaining clinical restorations (crowns, inlays, onlays, etc.) was considered and the main directions of the development of innovative ceramic materials for dental prosthetics were outlined. Based on the analysis of the properties of various types of materials for dental prosthetics, the prospects of using glass-ceramic materials in the development of dental prostheses have been substantiated. The chemical compositions of lithium silicate glasses for the synthesis of the glass matrix have been developed and the technological parameters for the production of glass-ceramic dental prostheses have been selected (Тgl. melting = 1350–1400 °С, Тheat treatment = 600–650 °С). Preliminary heat treatment before the formation of products ensures the formation of the required number of the nucleus of crystalline phase and the prerequisites for creating a volume crystallized structure under conditions of short-term heat treatment. The glass-ceramic prosthesis with a formed interpenetrating sitallized structure was obtained by the method of hot pressing with a short exposure (18-20 min). It was found that the obtained glass-ceramic material containing lithium disilicate as a crystalline phase in an amount of 40-60 vol. %, had high values of bending strength (σ = 400 MPa) and fracture toughness. The indicated mechanical properties of the developed materials, along with the approximate values of their modulus of elasticity to natural teeth, will significantly extend the service life of products under conditions of significant alternating loads that arise during the chewing cycle. A comparative assessment of the competitiveness of the developed dental prostheses based on lithium disilicate with world analogues was carried out, in particular the products of Ivoclar Vivadent and Vita Zahnfabrik, in terms of the main operational parameters. The positive effect of the introduction of domestic developed glass-ceramic dental prostheses to reduce import dependence has been determined.

A comprehensive study on the mechanical properties of Yb2SiO5 as a potential environmental barrier coating

Yb2SiO5 is a promising damage tolerant material to be used as an environmental barrier coating (EBC) for silicon-based ceramic substrates. However limited research is available on its mechanical properties, thus hindering the detailed evaluation of its performance as a possible EBC candidate. In this work, dense Yb2SiO5 is synthesized from Yb2O3 and SiO2 and sintered at 1580 °C. The mechanical properties of the material, including Young's modulus, Vickers hardness and fracture toughness are comprehensively studied to better understand the reliability of Yb2SiO5 as an EBC. Yb2SiO5 has a low Young's modulus of 119 GPa leading to low thermal stresses when deposited on a SiC/SiC substrate. It also has a low hardness value of 6.4 GPa, but a comparatively high fracture toughness value of 1.97 GPa. The effect of different loads on hardness was also investigated and it was noted that Yb2SiO5 exhibits reverse indentation size effect (ISE). This suggests that Yb2SiO5 undergoes relaxation when loaded. These promising results show that Yb2SiO5 could be used as a potential candidate for EBC applications.

Fabrication of (TixZr1−x)B2-(ZrxTi1−x)N composites by reactive spark plasma sintering of ZrB2-TiN

In this study, microstructural and mechanical properties of (ZrxTi1−x)N-(TixZr1−x)B2 composite fabricated by reactive spark plasma sintering (SPS) of ZrB2 and TiN was investigated. ZrB2 and TiN starting materials with equimolar ratio were sintered at 2000 °C for 8 min under a pressure of 30 MPa. An expansion (about 4%) was observed during the sintering process of the composite in the temperature range between 1290 °C and 1625 °C, which was attributed to the reaction of the starting materials. XRD pattern of the fabricated composite revealed the formation of TiB2 and ZrN phases after the sintering process. It was found that (Ti0.91Zr0.09)B2 and (Zr0.92Ti0.08)N phases are formed after sintering. High values of Vickers microhardness (28 ± 0.2 GPa), flexural strength (706 ± 51 MPa) and fracture toughness (8.49 ± 0.92 MPa m1/2) were achieved for this composite. Fracture of the (ZrxTi1−x)N and (TixZr1−x)B2 phases and crack path deflection mechanisms was founded as dominant toughening mechanisms in this composite.

Effect of support type on the fracture toughness and energy of asphalt concrete at different temperature conditions

This research deals with the effect of support type on the fracture toughness and fracture energy of asphalt concrete at various temperatures of −20, −10, 0, 10 and 20 °C. Fracture experiments were conducted on the SCB specimens using three different types of support including roller, roller-in-groove and fixed supports. Both the fracture toughness and the fracture energy of asphalt concrete reduced as the temperature enhanced. The results of fracture toughness and fracture energy showed that their values were highly dependent on the type of supports due to existing friction forces at the support boundary conditions. The fixed support type provided the highest values of fracture toughness and energy, and those for the roller-in-groove and roller support types were in the next ranks. From finite element modeling, the friction coefficients of 0.03 and 0.1 were finally found to be suitable to take account of friction effects in the roller-in-groove and fixed support cases. The results also revealed that the fixed support type was not suitable for measuring the fracture parameters of asphalt concrete particularly at the temperatures over 0 °C.