Vickers Indentation Fracture Toughness Research Articles

Effect of Y2O3 on crystallization and mechanical properties of sodium aluminum silicate glass containing ZrO2

In this paper, high transmittance glass-ceramics containing Zirconium Yttrium Oxide (Zr0.82Y0.18O1.91) nanocrystals were successfully prepared by melt cooling and crystallization heat-treatment method. The effects of Y2O3 concentration on the structure, crystallization performance, transmittance, and indentation fracture toughness of Na2O–Al2O3–B2O3–SiO2–ZrO2 glass and glass-ceramics were explored. The addition of Y2O3 improved the Vickers hardness (4.81 GPa–5.25 GPa) and indentation fracture toughness (0.78 MPam1/2 to 0.95 MPam1/2) of the glasses. Y2O3 successfully facilitated the precipitation of the non-alkaline crystalline phase Zr0.82Y0.18O1.91 at low heat-treatment temperatures. The precipitation of Zr0.82Y0.18O1.91 nanocrystals improves the Vickers hardness (5.17 GPa–5.56 GPa) and indentation fracture toughness (0.90 MPam1/2 to 1.01 MPam1/2) in glass-ceramics, while concurrently preserving a high level of visible light transmittance (∼90 %). This demonstrates its potential applications in the field of protective covers for electronic displays.

Microstructure, mechanical properties, and bone cell interactions of ZTA composites reinforced with BN

Due to their remarkable mechanical properties and biocompatibility, zirconia toughened alumina (ZTA) based composites are preferred materials for dental and orthopedic uses. This study focuses on the production and characterization of hexagonal boron nitride (BN) containing ZTA ceramics. To achieve this, we formulated composite systems with a composition of 70Al2O3-(30-x)YSZ-(x)BN (in vol%, where x ranges from 1 to 5). These mixtures were densified via spark plasma sintering (SPS) at a temperature of 1350 °C under a pressure of 40 MPa, with a dwell time of 5 min. The densification, resulting microstructure, and mechanical properties, including Vickers hardness and indentation fracture toughness, were thoroughly examined. All ZTA-BN composites achieved sintering densities exceeding 98.5% of their theoretical values. Incorporating BNs into ZTA composites increased fracture toughness by ∼55% while maintaining Vickers hardness values. Notably, crack deflection mechanism played a dominant role in toughening, particularly for the composite containing 3 vol% BNs. Furthermore, in vitro biocompatibility assessment of the YZTAB3 sample demonstrated that the composite had no cytotoxic effects towards human bone cells, indicating its potential for biomedical applications.

Microstructural evolution and mechanical properties of Ti(C,N)–FeCrMo-based green cermets

This work aims to develop Co and Ni-free Ti(C,N)–Fe-based cermets which are essential for developing cermets in the direction of green and low-cost materials. TiC and Ti(C,N) -based cermets prove to evince excellent mechanical properties at high temperatures as compared to conventional WC-based cermets. A binder system based on Cr, Mo, Fe, and their alloys may offer a viable solution to replace carcinogen elements such as Ni and Co from the binder. In the present work, high chromium Ti(C,N)-30 wt% FeCrMo cermets were fabricated by using Pressureless liquid-phase sintering. Samples at different sintering temperatures were prepared to investigate the influence of the temperature on microstructural formation and their mechanical characteristics. Scanning Electron Microscopy (SEM) is employed to observe the microstructural formation. A microstructural analysis of the consolidated cermets reveals that the addition of Mo to the binder system and an increase in sintering temperature affect the carbide grain size and densification, which ultimately affect their mechanical characteristics. The hardness and fracture toughness were determined by the Vickers hardness test and Indentation fracture toughness (IFT) method respectively. The maximum Hardness, Fracture toughness, and Transverse rapture strength achieved for the Ti(C,N)–FeCrMo-based green cermets are 665 ± 6.7 MPa, 1396 ± 26 HV30, and 9.23 ± 0.12 MPa m1/2 respectively.

Zirconia-Based Ceramics Reinforced by Carbon Nanotubes: A Review with Emphasis on Mechanical Properties

This review outlines the state of the art, processing techniques, and mechanical testing methods of zirconia (ZrO2)-based composites reinforced by carbon nanotubes (CNTs). The use of CNTs as a secondary phase in a zirconia matrix is motivated by their outstanding crack self-healing ability, the possibility to tailor the desired nano-structural properties, and their exceptional wear behavior. Therefore, a detailed investigation into CNT features has been provided. The debate of using the different Vickers indentation fracture toughness equations to estimate the resistance of crack propagation was critically reviewed according to crack characteristics. Finally, this review particularly highlights the exceptional role of ZrO2-based composites as a promising material owing to their outstanding tribo-mechanical properties.

Comparative Study of Conventional and Microwave-Assisted Boriding of AISI 1040 and AISI 4140 Steels

In this study, AISI 1040 and AISI 4140 steels were boriding using Ekabor-II commercial boriding powder with powder-pack boriding method using microwave and conventional heating methods. The samples were borided at 950 °C for 2 and 6 hours in an Ar atmosphere in a microwave oven of Enerzi-Mh2912-V8. Biphasic structure (FeB/Fe2B) was formed in all borided AISI 4140 samples and AISI 1040 samples borided for 6 hours. A single-phase structure was observed in AISI 1040 steel borided for 2 hours. Compared to the conventional method, a 1.5-1.6 times thicker boride layer was obtained in AISI 4140 and AISI 1040 steels with microwave-assisted powder-pack boriding. The highest hardness was measured as 1561.8 HV0.05 for boriding AISI 4140 steel and 1499.7 HV0.05 for boriding AISI 1040 steel. The Vickers indentation fracture toughness of borided steels with microwave energy varied between 2.31 and 3.46 MPa·m1/2. It was determined that in all samples borided by the microwave-assisted and conventional powder-pack boriding method, the adhesion strength between the boride layers and the substrate obtained was sufficient.

Microstructure and Mechanical Properties of HfC-SiC Ceramics Influenced by WC Addition.

The development of HfC-SiC has been challenging due to difficulties in achieving sintering and satisfactory mechanical properties. However, this study aims to overcome these limitations by incorporating WC as an additive. SPS was employed to process HfC-SiC and HfC-SiC doped with 5 vol.% WC. The resulting samples were then evaluated for their oxygen content, relative density, Vickers hardness, bending strength, indentation fracture toughness, and microstructure. The Vickers hardness (20.50 ± 0.20 GPa), flexural strength (600.19 ± 84.00 MPa), and indentation fracture toughness (5.76 ± 0.54 MPa·m1/2) of HfC-30 vol.% SiC-5 vol.% WC ceramics are higher than HfC-30 vol.% SiC ceramics. Doping 5 vol.% WC in HfC-30 vol.% SiC not only reduces the oxygen content of samples but also produces the (Hf,W)C solid solution and refines the microstructures, which are the main reasons for the higher mechanical properties of HfC-30 vol.% SiC-5 vol.% WC ceramics. In summary, this study successfully addresses the challenges associated with HfC-SiC by incorporating WC as an additive, leading to improved mechanical properties and microstructures.

Using vacancies to tune mechanical and elastic properties in La3−xTe4, Nd3−xTe4, and Pr3−xTe4 rare earth telluride thermoelectric materials

Elastic and mechanical properties in advanced RE3−xTe4 (RE = La, Pr, Nd) thermoelectric materials are found to depend considerably on cation vacancy concentration x. Increasing x, which simultaneously reduces charge carrier concentration from metal-like to semiconductor-like, leads to significant stiffening of elastic constants due to charge carrier effects. The coefficient of thermal expansion in La3−xTe4 determined by high temperature X-ray diffraction correspondingly decreases with x, indicating that thermal expansion may be tuned by x in RE3−xTe4 materials systems. Vickers indentation hardness and fracture toughness tests show similarly significant effects of x on hardness and mode I fracture toughness, both of which decrease with increasing x. The mechanical property trends are counter-intuitive and merit further investigation, but demonstrate overall that higher x in RE3−xTe4 leads to more brittle behavior. The combined results show the importance of intrinsic defects in RE3−xTe4 and the potential to tune the mechanical performance of RE3−xTe4 for practical implementation in next-generation thermoelectric devices.

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

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

Oxidation behaviour and its effect on fracture toughness of Niobium metal

Niobium metal was studied for its oxidation behaviour at different temperatures (800, 1000 & 1200 °C) and time (1, 3 & 5 h). The study revealed that Nb underwent oxidation forming pro-active Nb oxides with initial formation of meta-stable Nb12O29 which forms as an oxidisation resistant layer. However, formation of Nb2O5 from a meta-sable Nb12O29 did not act as protective layer as it exposed underneath to further oxidation leading to cracks. The oxidation kinetics of Nb shown a linear behaviour and the devised mathematical model using Deal Grove determined the thickness of oxide layers. The un-protectiveness of Nb2O5 was verified by the Vickers hardness (8.06 ± 0.4 GPa) and indentation fracture toughness (28.14 ± 0.4 MPa.m1/2) of material which decreased with increase in oxidation temperature.

Role of graphene in enhancing indentation and scratch properties of soda lime silicate glass

In this work, the role of graphene on indentation and scratch properties of soda lime silicate (SLS) glass is investigated by nanoindentation and nanoscratch as well as Vickers indentation tests. The results show that compared with bare SLS glass, the nanohardness and reduced modulus of graphene coated on SLS (G/SLS) glass are higher, because G/SLS glass surface can accommodate more strain energy through elastic process. The nanoscratch resistance of G/SLS glass is increased by ∼30%-44%, since the monolayer graphene can effectively reduce the friction force and activation volume of SLS glass during the mechanochemical wear process in humid air. Furthermore, the subsurface damage of G/SLS glass upon nanoindentation and nanoscratch tests are reduced, and the Vickers hardness and indentation fracture toughness of G/SLS glass are increased. These results clearly show the monolayer graphene can protect the SLS glass surface from physical contact via both normal and tangential shear tests.

Comparison between different fracture toughness techniques in zirconia dental ceramics.

Vickers indentation (IF) and single-edge-V-notched beam (SEVNB), to measure the fracture toughness (KIC ) of zirconia-based dental ceramics and mathematical models were proposed to establish a correlation between both. Zirconia (ZrO2 ) stabilized with 3mol. % of Y2 O3 (3Y-TZP) and 5mol% of Y2 O3 (5Y-PSZ) were compacted (n=42) and sintered for 2h at different temperatures (1475°C, 1500°C, 1550°C, or 1600°C). After sintering, they were characterized by relative density using the ASTM C373-88 standard, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average grain size was measured according to the ASTM E1382-97 standard. The fracture toughness (KIC ) was determined using two methods: Vickers indentation fracture toughness (KIC-IF ): method based on mathematical modeling that considers the parameters used for the Vickers hardness test and Fracture toughness by the single-edge-V-notch-beam (KIC-SEVNB ): method proposed by ISO 23146:08. The main phases of the 3Y-TZP and 5Y-PSZ ceramics were ZrO2 -tetragonal and ZrO2 -cubic, respectively. The 3Y-TZP specimens showed equiaxed grains with average grain sizes ranging from 0.55 to 0.79 μm. The grain sizes of 5Y-PSZ of specimens sintered at 1475°C and 1600°C were 0.62 and 2.32 μm, respectively. For all ceramics the crack size ratio was c/a < 2.5, suggesting a Palmqvist-type crack system. The fracture toughness measured by the Vickers indentation method (KIC-IF ) and by the SEVNB method (KIC-SEVNB ) was the same when the experimental data were fit to a mathematical model.

Synthesis, microstructure and properties of Ti(C,N)-(HfZrTaNbTi)C5-HEA high-entropy cermets by high-energy ball milling and spark plasma sintering

High-entropy carbide ceramics have received extensive attention because of their excellent mechanical properties and better oxidation resistance. However, the additive phase of Ti(C,N)-based cermets has not been reported yet. In this study, (HfZrTaNbTi)C5 high-entropy ceramics (HECs) with equal atomic ratios were successfully prepared by high-energy ball milling. The results show that the HECs possess a single-phase cubic rock salt structure, fine grains, and a uniform element distribution. Then, it was used as the additive phase of Ti(C,N)-based cermets. And with AlCoCrFeNi2.1 high-entropy alloy (HEA) as binder, Ti(C,N)-HECs-HEA high-entropy cermet block materials was successfully prepared by SPS technology. The room temperature mechanical properties and high-temperature oxidation properties of high-entropy cermets have been studied. The results show that unlike traditional Ti(C,N)-based cermets, the hard phase of high-entropy cermets is composed of black core-white inner ring-grey outer ring grains and grey grains. The grey contrast phase is the newly formed (HfZrNbTaTi)(C,N) high-entropy ceramic phase. Compared with traditional Ti(C,N)-based cermets, high-entropy cermets not only have a considerable hardness (1780.3 HV) but also have relatively higher Vickers indentation fracture toughness (9.22 MPa m1/2) and bending strength (1315 MPa). After being oxidized in air at 1000 °C for 60 min, the high-entropy cermets shows excellent oxidation resistance, with a dense oxide layer and fine oxide particles. The continuous and dense oxide layer effectively prevents the transport of oxygen into the cermets matrix. And the lattice distortion effect and slow diffusion effect of high-entropy alloys and high-entropy ceramics retard the diffusion of elements.

Study of Lithium Disilicate Based Nano Glass Ceramics Containing P2O5

Multi component lithium disilicate based glasses containing P2O5 have been synthesized by conventional melt quenching technique. The replacement of (Li2O + SiO2) by P2O5 and its nucleating effect has been discussed. Structural features of glasses were evaluated by differential thermal analysis (DTA), Fourier transform infrared (FTIR) and Raman spectroscopy. The glass samples have been converted into glass ceramics by following three stage heat treatment schedules. X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), high angle annular dark field imaging (HAADF), energy dispersive X-ray analysis (EDX) and high resolution transmission electron microscopy (HR-TEM) has been carried out for the glass ceramics. Vickers microhardness (Hv) and Vickers indentation fracture toughness (KIC) of all the glass ceramics have been measured. UV–Visible spectroscopy study has been carried out for glass ceramics to investigate the optical properties. The glass ceramic with 1.5 mol % P2O5 has the highest transmittance. Glass ceramics with P2O5 ≥ 1 mol % having Li2Si2O5 (LS2) as main phase exhibit high Hv about 6.71–6.82 GPa which is suitable for dental and armor applications.

10 - Functionalization of Restorative Dental Glass-Ceramics with Bactericidal Properties

Clinically, the periodontitis is related with the dental plaque, a biofilm of microorganisms, growth on the gum line and on the tooth interface. Therefore, a strategy to minimize this condition is the functionalization of the dental prosthesis, usually in contact with the gum, with antibacterial properties. The purpose of this study was to investigate the bactericidal potential of some commercial restorative glass-ceramic materials and to functionalize a commercial dental porcelain with antibacterial properties. Commercially available restorative glass-ceramics in powder (IPS d.SIGN), or as monolithic (IPS E.max Press e GC Initial LiSi Press) were used as control samples, and characterized by X-ray diffraction (XRD), Rietveld refinement, differential thermal analysis and particle size distribution. The IPS d.SIGN glass-ceramic was selected for functionalization with nanostructured β-AgVO 3 that was synthetized by a hydrothermal route, using AgNO 3 and NH 4 VO 3 as precursors, and characterized by XRD and Scanning Electron Microscopy (SEM). The glass-ceramic material was mixed with different percentages (1%, 2%, 4% or 6%wt) of β-AgVO 3 , uniaxially pressed at 50 MPa, and thermally treated at 900 C for 5 min, as indicated by the manufacturer. The functionalized glass-ceramics was characterized by XRD, Rietveld refinement, SEM, Vickers Hardness and Vickers indentation fracture toughness. The three commercial glass-ceramics, IPS d.SIGN, IPS E.max Press and GC Initial LiSi Press as well as the functionalized samples were evaluated for its bactericidal potential against model bacteria (Escherichia coli and Staphylococcus aureus). The as-received control samples presented leucite (KAlSi 2 O 6 ) as the only detectable crystalline phase, 62%wt of amorphous phase and a median particle size (D50) of 25.5 m in IPS d.SIGN. The product of the hydrothermal synthesis was characterized as pure needle like shaped β-AgVO 3 crystals. The heat-treated control samples still presented KAlSi 2 O 6 as the only detectable crystalline phase. However, a secondary feldspar (KAlSi 3 O 8 ) phase could be detected in the functionalized samples, which turns to be the main crystalline phase as a function of the increase in the β-AgVO 3 concentration. None of the commercially available samples showed antibacterial activity, but the IPS d.SIGN samples functionalized with 2%wt or more of β-AgVO 3 presented a clear inhibition halo, from 12, 70, 3 mm to 15, 50, 1 mm, suggesting bactericidal activity against both model bacteria. Preliminary, in vitro results indicated that the analyzed commercial dental glass ceramics demonstrated no antibacterial activity. Nevertheless, the functionalization of a commercially available veneering glass-ceramic with at least 2%wt of β-AgVO 3 can induce bactericidal activity against gram-positive and gram-negative bacteria.

Environment dependence of hardness and fracture toughness of soda lime silica glass in humid and liquid conditions

In this work, the Vickers indentations are made on soda lime silica (SLS) glass surface in humid air (40% RH) and liquid water as well as in acid and basic solutions, to study the environment effects on Vickers hardness (HV) and indentation fracture toughness (KIC). The results show that the HV and KIC of SLS glass in 40% RH is higher than that in liquid water, which is caused by the enhanced water-induced hydrolysis of Si-O-Si network in liquid conditions, as revealed by more OH groups inside the Vickers indentation from Raman spectra. Moreover, the HV of SLS glass in neutral conditions is higher than that in non-neutral solutions, but the apparent KIC in neutral conditions is lower than that in non-neutral solutions, which is due to the lower densification ratio in neutral conditions. The dissolution of densified region in high pH conditions and lower rate of crack propagation in low pH conditions are responsible for the slight difference in KIC in extreme conditions.

Shrinkage rate control during a flash state by current‐ramping for 3 mol% Y2O3‐doped ZrO2 polycrystals

Abstract3 mol% Y2O3‐doped ZrO2 green compacts with rectangular shapes were sintered by maintaining the shrinkage rates at constant values under alternating electric fields by ramping the electric current during flash states. Green compacts were furnace‐heated under 40‐100 Vrms/cm until current hits an initial current limit of 100 mArms. After then, current‐ramping was started to keep the shrinkage rates constant by increasing the limit current value using a programmable power supply operating in a current control mode. Highly densified 3 mol% Y2O3‐doped ZrO2 polycrystals with a density of 6.05 g/cm3 as a bulk density and a grain size of about 0.4 μm were obtained at a furnace temperature of about 930℃, 50 Vrms/cm with 1000 Hz and shrinkage rate of about 120 μm/min (0.8%/min against initial lengths of green compacts). The Vickers hardness and indentation fracture toughness of the compact exhibit similar values to those obtained from thermally sintered compacts.

Microstructure and mechanical properties of B4C-NbB2-SiC ternary eutectic composites by a crucible-free zone melting method

Directionally solidified B4C–NbB2-SiC ternary composites were prepared by a floating zone method based on crucible-free zone melting of compacted powders. The ternary eutectic composition of B4C–15NbB2–35SiC (mol.%) was characterized by a boron carbide matrix, directionally reinforced by lamella-type NbB2 and SiC phases. NbB2 and SiC inclusions about 1−2 μm in thickness were uniformly dispersed in B4C matrix of B4C–NbB2–SiC eutectic composite. The Vickers hardness and indentation fracture toughness of the B4C–NbB2–SiC ternary eutectic were 35.8 GPa and 6.4 MPa m1/2, respectively.

Mechanical properties and oxidation behavior of spark plasma sintered (Zr,Ti)B2 ceramics with graphene nanoplatelets

This research focuses on the production and characterization of (Zr,Ti)B2 solid solution systems. The purpose of this study is to understand how solid solution formation influences the structure, mechanical properties, and oxidation resistance of ZrB2 and TiB2. For this, herein, monolithic ZrB2, TiB2, and (ZrxTi1-x)B2 solid solution systems (x = 0.25, 0.50, 0.58, 0.75) were prepared. Moreover, 1 vol% graphene nanoplatelets (GNPs) were added to two different solid solution systems (Zr0.25Ti0.75B2 and Zr0.58Ti0.42B2) without affecting the complete solid solubility of these systems. All powder mixtures were densified by spark plasma sintering at 1800 °C, under 50 MPa with 5 min holding time. The densification, oxidation behavior, microstructure, phases, and mechanical properties (Vickers hardness and indentation fracture toughness) of these samples were systematically investigated. The formation of solid solutions caused an increase in the Vickers hardness and fracture toughness of the samples. Further improvement in mechanical properties and better oxidation resistance were achieved with the addition of GNPs to the solid solution systems.

Hardness and Indentation Fracture Toughness of Slip Cast Alumina and Alumina-Zirconia Ceramics.

Alumina (Al2O3) and zirconia (ZrO2) have good overall properties and thus are widely used oxide technical ceramics. The biggest drawback of Al2O3 is its low fracture toughness. In contrast, ZrO2 is relatively tough, but is also much more expensive. In order to improve the alumina toughness, composite ceramics are being developed. Slip casting technology has economic advantages over the conventional hot isostatic pressure technology, but problems may arise when preparing stable highly-concentrated suspensions (slip) for filling the mold. The purpose of this study is to prepare aqueous suspensions using 70 wt. % α-Al2O3, with 0, 1, 5 and 10 wt. % of added t-ZrO2. Suspensions were electrosterically stabilized using the ammonium salt of polymethylacrylic acid, an alkali-free anionic polyelectrolyte dispersant. Also, magnesium oxide in form of magnesium aluminate spinel (MgAl2O4) was used to inhibit the abnormal alumina grain growth during the sintering process. Minimum viscosities were used as stability estimators, where an increase in ZrO2 content required adding more dispersant. After sintering, the Vickers indentation test was used to determine the hardness and the indentation fracture toughness from the measurement of the crack length. Also, the brittleness index (Bi, μm−1/2) was calculated from values of Vickers hardness and the Vickers indentation fracture toughness. It was found that with increasing ZrO2 content the fracture toughness increased, while the hardness as well as the brittleness index decreased. Zirconia loading reduces the crystallite sizes of alumina, as confirmed by the X-ray diffraction analysis. SEM/EDS analysis showed that ZrO2 grains are distributed in the Al2O3 matrix, forming some agglomerates of ZrO2 and some pores, with ZrO2 having a smaller grain size than Al2O3.

Properties of TiC and TiN Reinforced Alumina–Zirconia Composites Sintered with Spark Plasma Technique

In this paper, Al2O3–ZrO2 composites with an addition of 20 wt% TiN and 10 wt% TiC were modified. The addition of zirconia in a range from 2 to 5 wt% of the monoclinic phase and 10 wt% of Y2O3 stabilised ZrO2 affected the mechanical properties of the composites. A new type of sintering technique—the spark plasma sintering (SPS) method—within a temperature range from 1575 °C to 1675 °C, was used. Vickers hardness, apparent density, wear resistance and indentation fracture toughness KIC(HV) were evaluated at room temperature. An increase of the sintering temperature resulted in an improvement of Vickers hardness and an increase of the fracture toughness of the tested composites. The tribological properties of the samples were tested using the ball-on-disc method. The friction coefficient was in a range from 0.31 to 0.55, depending on the sintering temperature. An enhancement of the specific wear rate was dependent on the sintering temperature. The mechanical properties of the samples sintered by pressureless sintering (PS) were compared. X-ray diffraction patterns were presented in order to determine the phase composition. SEM microstructure of the tested composites sintered at different temperatures was observed.