Indentation Fracture Research Articles

Improved mechanical and tribological properties of (TiZrHfNbTa)C with the addition of silicon carbide whiskers

Dense (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with up to 10 wt % SiC whisker were prepared by spark plasma sintering. The influence of SiCw on the microstructure development, mechanical and tribological properties has been investigated. Nanohardness of HEC and SiCw phases varied between 38 GPa and 40 GPa, and indentation modulus of elasticity was ∼605 GPa. The hardness of the composites increased from 22 GPa to 27 GPa and indentation fracture resistance from 3.55 MPa m1/2 to 4.59 MPa m1/2 with increasing SiCw content. The main toughening mechanisms were crack deflection, crack branching, and crack bridging. The system HEC +5 wt% of SiCw was found to possess the highest bending strength of 623 ± 25 MPa. The composites exhibited similar coefficients of frictions with around 0.3 and wear rates approximately 1.50 × 10−6 mm3/N⋅m at 5 N and 2.66 × 10−6 mm3/N⋅m at 25 N with positive influence of SiC phase on the wear mechanisms.

Experimental analysis of quasi‐static indentation in composite sandwich multilayers with corrugated core

AbstractThis study examines the effects of multilayering in sandwich panel composite structures with different corrugated core configurations under quasi‐static indentation loading. The panels were fabricated using woven glass fibers and epoxy resin via the Vacuum Infusion Process. Experiments were conducted using two hemispherical cylindrical indenters with a diameter of 20 mm (ID = 20 mm) and 10 mm (ID = 10 mm) and the behavior of the composite structure in terms of contact force and fracture mechanisms for different core corrugations (square and butterfly) were investigated in two ways with foam and without foam. The experimental results demonstrate that, among corrugated core geometries without foam, butterfly cores outperform square cores in terms of structural strength, maximum force, moment force, energy absorption, specific energy absorption, and displacement until full indentation. Moreover, the butterfly core shows a higher peak load and different failure mechanisms compared to the square core. Under loading with a 10 mm indenter, the butterfly core without foam only experienced perforation in the loading area, without fracture completely. Also, adding foam did not change failure mechanisms and mechanical behavior in the butterfly geometry. However, in the square geometry, foam filled gaps between the core, preventing fracture completely and leading to only perforation in the loading area, unlike the specimen without foam. The visual analysis during the quasi‐static indentation process revealed several significant damage mechanisms, including matrix cracking, fiber breakage, delamination, buckling and crushing of cell walls, damage to top sheets, core separation, and complete indentation of the samples.Highlights Delamination and indentation failure mechanisms were seen on the butterfly core. Skin indentation and rib fracture failure mechanisms were seen on the square core. Butterfly corrugated cores revealed the best performance without/with foam. The core shape was more effective on the strength than the foam addition.

Enhanced mechanical properties in transparent mullite glass-ceramics synthesized from EMT-type zeolites via spark plasma sintering

Transparent glass-ceramics offer a unique combination of optical clarity and the mechanical strength of ceramics, making them ideal for various advanced applications such as cell phone screens and telescope mirrors. However, traditional fabrication methods involve high temperatures and long processing times, which result in high energy consumption and limitations in material integration. In this study, we explore the fabrication of transparent mullite glass-ceramics from EMT-type zeolites using the spark plasma sintering (SPS) technique to address these challenges. By varying the concentrations of ammonium salts to replace Na+ in the zeolite, we modified the SiO2+Al2O3 content and successfully synthesized the mullite glass-ceramics at 950 °C. The resulting glass-ceramics exhibited high transmittance (>65 % in the visible region), improved mechanical properties with a Young's modulus up to 103 GPa, a Vickers hardness of 8.0 GPa, and an indentation fracture toughness of 1.8 MPa m1/2. X-ray diffraction and Raman spectroscopy confirmed the formation of mullite phases, with increased crystallinity and a strengthened glass structure, correlating with higher SiO2+Al2O3 content. The study demonstrates the potential of using high Al/Si ratio molecular sieves as precursors for high-performance glass-ceramics, offering significant advancements in both optical and mechanical properties.

Mathematical modelling and validation of the mechanical properties of HVOF-sprayed WC-12Co coatings considering the phase composition and defects generated at different process parameters

The thermal spraying process involves many machine-based parameters or independent variables (fuel flow rate, oxygen flow rate, powder feed rate, stand-off distance and many others in the HVOF process). Any combination of these parameters produces only two measurable responses, namely, particle temperature and particle velocity. In this current work, first, the machine-based spray parameters are varied in specific ways to produce different particle temperatures at near-constant velocities and vice-versa. This approach has reduced the number of independent variables to only two. These two factors further influence the in-flight particle reactions, thereby affecting the phase composition and the microstructural defects in the as-sprayed coatings. The X-ray diffraction patterns of the as-sprayed coatings revealed the presence of W2C, W, Co3W9C4, and amorphous Co-W-C phases apart from the WC phase. The W2C and W originated owing to the decarburization of the WC phase. On the other hand, the dissolution of the carbide in molten binder led to the formation of Co3W9C4 and the amorphous Co-W-C phase. The nano-hardness of both the carbide and binder phases increased with an increase in particle temperature owing to a higher degree of decarburization and carbide dissolution respectively. The porosity was the most significant micro-structural defect present in the as-sprayed coatings. An increase in either particle temperature or velocity reduced the porosity present in the as-sprayed coatings. The mechanical properties (microhardness, elastic modulus and indentation fracture toughness) tend to improve as porosity decreases. A comprehensive mathematical model was proposed to predict the mechanical properties of as-sprayed coatings as a function of composition and defects. Finally, the process maps of mechanical properties were plotted in temperature-velocity space.

Effect of processing parameters and carbon to metal ratio on microstructure and mechanical properties of (MoTaTiVW)Cx high entropy carbide produced by reactive spark plasma sintering

(MoTaTiVW)Cx high entropy ceramics with varying carbon to metal ratio in the range of 0.75-0.97 were synthesized by by reactive spark plasma sintering. The effect of ball milling time on particle size, phase evolution and carbon pick-up due to toluene decomposition were studied. Formation of single-phase high entropy carbide having face-centered cubic (FCC) crystal structure was confirmed by X-ray diffraction (XRD), electron backscattered diffraction (EBSD) and Selected area diffraction pattern (SAED) analysis of the sintered compacts. Transmission Kikuchi Diffraction images revealed presence of equiaxed nature of the grains. Transmission electron microscopy images revealed the presence of an intergranular phase at grain boundaries and triple junctions. 3D-Atom Probe Tomography studies showed uniform distribution of elements within the grains with some segregation of impurity elements Fe and Co to the grain boundaries indicating minor contribution of liquid phase sintering to densification. The grain size of single-phase sintered compacts ranged between 1.69 ± 0.60 μm to 4.6 ± 1.0 μm. A low sintering temperature and higher milling time resulted in finer grain size The microhardness was found to increase with milling time and C/M ratio. The microhardness, Young’s modulus and indentation fracture toughness lied between 2221 HV0.1 to 2732 HV0.1, 370 GPa to 473 GPa, 3.6 MPa.m1/2 to 4.4 MPa.m1/2, respectively. The highest microhardness and indentation fracture toughness was found to be 2732 ± 80 HV0.1 and 4.4 MPa.m1/2 on par with reported literature for other high entropy carbides.

Effects of sintering temperature on the microstructure and mechanical properties of double-hard-phase TiB2–TiC cermets

The mechanical properties and microstructure of double-hard-phase TiB2–25-wt.%-TiC–20-wt.%-CoNi cermets prepared at different temperatures were investigated by performing scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results showed that the transverse rupture strength, indentation fracture toughness, hardness, and relative density of the cermets reached the maximum values of 1654 MPa, 11.06 MPa m1/2, 90.1 HRA, and 99.42 %, respectively, when the sintering temperature was 1462 °C. Solid- and liquid-phase sintering occurred at temperatures below and above 1354.5 °C, respectively. The cermets were composed of TiB2, TiC, TiB, and CoNi phases when sintered at 1440 °C and below, but the TiB phase disappeared when sintered at 1462 °C and above. Both TiB2 core–(Ti, Co, Ni)B rim and TiC core–(Ti, Co, Ni)C rim structures appeared in cermets sintered at 1440 °C and above. In addition, a few TiC core–(Ti, W)C inner–(Ti, W, Co, Ni)C outer double rim structures were formed. A coherent interface was found between the (Ti, Co, Ni)B rim and TiB2 core. A thin CoNi amorphous metallic layer existed at the interface between the (Ti, Co, Ni)C rim and TiC core. In addition, amorphous CoNi was observed in the interfacial region between the CoNi binder and (Ti, Co, Ni)C rim phase and inside the CoNi binder phase. These multi-interface and core–rim structures resulted in excellent strength and toughness of the cermets.

A comparative study on nanoscale mechanical properties of CrMnFeCoNi high-entropy alloys fabricated by casting and additive manufacturing

Additive manufacturing (AM) has emerged as a pioneering method for fabricating high entropy alloys (HEAs), yet a comprehensive comparison of their nanoscale mechanical properties with those produced by the conventional casting method remains unexplored. In this study, the nanoindentation was utilized to investigate the nanoscale elastic and plastic characteristics in both additive-manufactured (AM-ed) and as-casted single-phase face-centered cubic (FCC) equiatomic CrMnFeCoNi HEAs. Herein, the hardness, reduced modulus, indentation size effect (ISE), yield strength, fracture toughness, and strain rate sensitivity were comprehensively investigated. The results indicated that the hardness of AM-ed HEA was higher than the as-casted HEA, and the reduced modulus values showed no notable distinction between the two samples. The AM-ed HEA demonstrated simultaneous enhancements in yield strength and fracture toughness compared to the as-casted HEA. The as-casted HEA possessed a more distinct indentation size effect (ISE) than the AM-ed HEA. It was observed that the AM-ed HEA exhibited relatively lower strain rate sensitivity and a larger activation volume. This direct comparison of the mechanical properties and deformation mechanisms from a nanoscale view offers unique insights for optimizing and advancing AM techniques in the fabrication of HEAs.

Surface roughness and fracture cracks of Al2O3/TiO2 composite coating by wet chemical mechanical grinding with structured abrasives pad

In the fields of wind power, and other industries, the Al2O3/TiO2 coating is prepared and ground on the bearing ring, in order to obtain the insulation resisting the electrical erosion for the motors at high voltage. A novel wet chemical mechanical grinding (WCMG) method is proposed to finish this hard-brittle composite material, utilizing the structured diamond abrasives pad and the NaOH solution. The softened workpiece's surface under the chemical reaction was demonstrated by means of Raman spectrum, indentation and scratching tests. The analytical model of surface roughness and fracture cracks is established based on the synthesis of geometry and kinematics, contact mechanics, material removal and indentation fracture mechanics. The surface roughness of coating was reduced from initial Sa 3.293 μm down to final Sa 0.049 μm in the WCMG process with grain size 3 μm and pH 12.01, mostly attributed to the ductile removal of chemically softened coating surface.

Densification, phase composition, microstructure and properties of spark plasma sintered La0.6Ce0.3Pr0.1B6 bulks

This paper studied the densification, phase composition, microstructure and properties of polycrystalline La0.6Ce0.3Pr0.1B6 bulks prepared by SPS. The dense specimen (98.9 % in relative density) with the average grain size of 15.46 μm has been determined to be a CsCl-type single-phase substitutional solid solution without any impurities or other secondary phases. The homogenous elemental distributions of La, Ce and Pr have been confirmed by both microscale and nanoscale. The room temperature (RT) Vickers hardness (Hv), indentation fracture toughness (KIC) and flexure strength of the dense specimen have been measured to be 23.0 GPa, 2.04 MPa m1/2 and 305.1 MPa, respectively. The Berkovich hardness (HB) and elastic modulus (E) of the dense specimen have been measured to be 30.0 GPa and 376.0 GPa, respectively, by nanoindentation tests at a maximum load of 40 mN. In comparison with the polycrystalline LaB6 bulk, the lower work function Φ of 2.64 eV evaluated by UPS and the larger thermionic emission current densities measured at the same operating condition suggest that the polycrystalline La0.6Ce0.3Pr0.1B6 bulk is a superior-performance thermionic cathode material.

A novel method for reducing the brazing temperature of C/C composite with TiZrHfTa/Ni composite interlayers

C/C composite was successfully brazed with TiZrHfTa/Ni composite interlayers at lower temperature far below the melting point of TiZrHfTa refractory high entropy alloy. The influence of brazing parameters on the joint morphology, indentation fraction toughness of the reaction layer, shear strength at room temperature and at 1000 °C, and fracture behavior was investigated. The results show that all of the C/C composite joints contained two main phases: an equimolar (Ti-Zr-Hf-Ta)C hard phase and a near-pure Ni binder phase. The maximum indentation fracture toughness of the obtained joint reaction layer material was 15.52 ± 0.64 MPa·m1/2. This was proved to be beneficial to improve the strength and toughness of the joint. Meanwhile, the maximum shear strengths of C/C-TiZrHfTa/Ni-C/C joint at room temperature and at 1000 °C reached 33.24 ± 1.85 MPa and 21.70 ± 2.12 MPa, respectively. Abundant slip lines, in-situ dimples, and tearing ridges resulting from Ni plastic deformation suggest a predominantly ductile fracture mode in the joint. This work introduces an innovative method, which can not only ensure the service of C/C composite in high temperature environment, but also effectively reduce the joining temperature.

Simultaneous effect of microwave sintering and TiO2 addition on sinterability, mechanical properties, and scratch resistance of zirconia toughened alumina ceramics

This paper delves into the transformative impact of varying titanium dioxide (TiO2) content on the sinterability, physical, and mechanical properties, as well as scratch behavior, of zirconia-toughened alumina (ZTA) ceramic composites. By adjusting TiO2 content from 0 wt% to 5 wt% and employing advanced microwave sintering at 1150 °C, the study aims to lower the sintering temperature of ZTA. Microwave sintering, known for its efficiency and rapid processing, enables significant enhancements in material properties at reduced temperatures. Notably, incorporating TiO2 into ZTA yields remarkable improvements in physical and mechanical attributes, with the optimal TiO2 content determined to be 3 wt%. At this concentration, the composite achieves exceptional properties: a relative density of ∼99 %, microhardness of ∼2002 HV, and an indentation fracture toughness of ∼6.13 MPa m0.5. These enhancements represent increases of over 120 % in hardness and 61 % in toughness compared to TiO2-free ZTA. Additionally, the highest scratch resistance is observed at 3 wt% TiO2, evidenced by a minimal scratch depth of ∼7.53 μm. However, exceeding the 3 wt% solubility limit results in the formation of secondary phases, such as tialite (Al2TiO5) and zirconium titanate (ZrTiO4), which degrade the composite's properties. This research underscores the potential of TiO2 doping and microwave sintering to elevate the performance of ZTA ceramics, offering a pathway to superior materials for advanced applications.

Additively manufactured Nb-Ti-Si based alloy: As-built and heat-treated conditions

This work aims to fully characterise the Nb-Ti-Si based alloy (Nb-26Ti-16Si-2.2Al-2Cr), processed by the electron-beam powder-bed-fusion in both as-built and heat-treated conditions, to elucidate the microstructure-property relationships. The as-built condition has [001]-oriented columnar grains of the Nb3Si phase with the Nbss phase dispersed throughout the microstructure. The microhardness is 645.2 ± 6.7 HV0.5, and the indentation fracture toughness shows distinct directionality: 7.7 MPa·m1/2 in the horizontal direction compared to 5.3 MPa·m1/2 in the vertical direction. Both properties are comparable to the cast version. The directionality is attributed to the underlying mechanisms such as crack bridging, arrest, and micro-crack formation. By contrast, in the heat-treated condition, the alloy exhibits a dual-phase microstructure (Nbss and Nb5Si3 phases) with near-equiaxed grain shape due to the Nb3Si phase decomposition. The fracture toughness increases to 12.1 MPa·m1/2, at the expense of a reduced microhardness of 564.4 ± 15.0 HV0.5.

Investigation of the failure behaviour of equiatomic AlCrCuNiFe based high entropy alloy TIG weld cladding

The present research focuses on the development of an equiatomic AlCrCuNiFe high entropy alloy (HEA) cladding using the TIG welding process. The influence and contribution of TIG cladding process parameters (welding current, welding speed, and SOD) on the microhardness and flexural stress have been investigated using the response surface methodology (RSM) and analysis of variance (ANOVA), respectively. The indentation fracture toughness test has been conducted over the claddings exhibiting minimum, maximum, and optimum microhardness values. The result revealed that welding current has the highest effect on the mechanical performance of the HEA cladding. The FE-SEM, optical microscopy, XRD and EDS analysis were performed to characterize the claddings. The cladding deposited at the S12 test run offered the least flexural resistance, microhardness, and indentation fracture toughness which was about 812 MPa, 494.97 HV0.3, and 1.29 ± 0.04 MPa.m1/2, respectively. In contrast, the optimized S5 cladding specimen exhibited good flexural resistance, appreciable microhardness and indentation fracture toughness of about 1543.92 MPa, 712 HV0.3, and 1.63 ± 0.03 MPa.m1/2 respectively. The optimum cladding exhibited flexural stress, microhardness, and fracture toughness enhancement of 46.77 %, 30 %, and 26.35 % compared to the least resistance cladding (S12) due to the high-retained alloying elements leading to enhanced solid solution strengthening. The three-point bend-tested cladding specimens’ optical microscopy images revealed that the cladding failure was primarily due to cohesive failure, crack progression, and delamination.

Ultra-high hard and fracture-resistant multi-phase nanocrystalline AlCrFeMoNbNi multi-principal element alloy

Multi-phase nanocrystalline AlCrFeMoNbNi multi-principal element alloy was developed using mechanical alloying followed by spark plasma sintering. Mechanical alloying resulted in a two-phase microstructure (BCC and FCC), whereas subsequent sintering resulted in a multi-phase microstructure consisting of FCC, Rhombohedral and B2 phases. Extremely high hardness values in the range of 35.79–16.05 GPa were measured as a function of indentation load between 25 and 5000 g. A highly pronounced indentation size effect was observed. From classic Nix-Gao analysis, a load independent hardness of 13.82 GPa was estimated. The high hardness arises from a combination of finer grain size and solid solution strengthening (FCC phase) and multi-phase structure consisting of B2 and Rhombohedral phases. The major phase being FCC (83%) offers nearly 85% of the total flow stress realized for this MPEA and the remaining 15% of the flow stress must be arising from both the B2 and Rhombohedral phases. It is to be noted that the phase fractions of B2 and Rhombohedral phases are 10% and 7% respectively. Indentation fracture toughness, evaluated using the cracks developed during Vickers indentation, yielded encouraging numbers in the range 12.28–13.85 MPam. The excellent combination of ultra-high hardness and indentation fracture toughness of this AlCrFeMoNbNi MPEA surpasses the reported data on several related harder materials, including silicides, nitrides, carbides, etc.

Evolution of microstructure and mechanical properties of TiB2-7.5 wt.% WC-based cermets sintered at different temperatures

The evolution of microstructure and mechanical properties of TiB2–7.5 wt% WC-based cermets sintered at different temperatures were investigated. The results showed that eutectic liquid phase appeared at around 1335 °C, indicating that solid-phase sintering occurred below that temperature, while liquid-phase sintering occurred above that temperature. TiB2, W2CoB2, WB and CoNi phases were detected in the XRD patterns of cermets sintered at different temperatures, and TEM analysis showed the presence of TiC phase. So the following chemical reaction should occur: TiB2 + WC + Co → W2CoB2 + WB + TiC. The TiB2 core - (Ti, W, Co, Ni)(B, C) rim phase were observed in the cermet sintered at 1397 °C. As the increase of sintering temperature, the solubility of WC and TiB2 in CoNi binder phase, and the number of core-rim structure hard phase particles increased. The formation of core-rim structure enhanced the interfacial bonding strength between TiB2 phase and CoNi binder, which was beneficial for improving the strength and toughness of cermets. The cermets sintered at 1465 °C had good comprehensive mechanical properties, with a relative density of 99.62%, a hardness of 17.34 ± 0.43 GPa, a transversal rupture strength of 2038 ± 53 MPa, and an indentation fracture toughness of 12.15 ± 0.32 MPa·m1/2.

Nano-, micro- and macro-indentation tests of thermal spray WC-Ni coatings with lamellar microstructure at different particle deposition temperatures

The mechanical properties of WC-Ni coatings by HVOF thermal spraying were comprehensively evaluated by indentation tests at a wide load range of 10−1-103 N, i.e. nano-, micro- and macro-indentations. The correlation between process parameters and coating microstructure and mechanical properties was characterized via particle deposition temperature. The coating microstructure changes in reduced porosity, enhanced WC phase decomposition and better splats flattening were correlated to the particle deposition temperature rising. A porosity divergence between coating surface and cross-section was found as a quantitative anisotropy indicator to coating intrinsic lamellar microstructure formed by the splats flattening and piling up. Considering the lamellar microstructure, indentation responses on coating surface and cross-section were compared for hardness and elastic modulus evaluation below 3 N. The surface hardness is higher than that of cross-section, and both increased correlatively to the particle deposition temperature rising except for the almost constant surface hardness below 1 N. An analogous particle temperature-dependent behavior was also manifested for the elastic modulus by nano-indentation below 1 N. Interestingly, the elastic modulus by coating surface micro-indentation at 30 N presented identical particle temperature dependence to that by coating cross-section nano-indentation, both consistently representing the overall coating elastic modulus change trend verified by non-destructive ultrasonic test. Indentation fracture toughness on coating surface under 1.96 kN and on coating cross-section under 49 N was comparatively evaluated, and the values had a reverse trend of dependence on the particle deposition temperature. The particle-deposition-temperature dependent mechanical properties were interpreted by the coating intra-splats and inter-splats defects reduction with enhanced carbide-metal bonding essentially determined by the melting state of the metal binder phase, providing an insight to utilize indentation tests for characterizing thermal spray coatings.

Are we approaching the development of a novel calcium phosphate-based bioceramic dental material?

ObjectivesDevelop a sustainable bovine hydroxyapatite dental ceramic with the addition of titanium dioxide (TiO2) nanoparticles (5 % and 8 % by weight), analyzing the outcome of this addition to the microstructure, as well as its mechanical and chemical properties, in order to evaluate whether they satisfy the International Organization for Standardization (ISO) 6872:2015 for dental ceramics or not. MethodsDisks were obtained through uniaxial followed by isostatic pressing from bovine hydroxyapatite powder and TiO2 nanoparticles and sintered at 1300ºC for 2 h. Three experimental groups were developed (HA, HA+5 %TiO2 and HA+8 %TiO2) and subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), indentation fracture (IF), biaxial flexural strength (BFS) and chemical solubility test. ResultsXRD revealed, for HA group, the appearance of a peak corresponding to b-tricalcium phosphate (ß-TCP). For HA+ 5 %TiO2 and HA+ 8 %TiO2, the entire composition was converted into ß-TCP and calcium titanate (CaTiO3). The SEM images showed a dense ceramic matrix and a uniform distribution of another phase in groups with TiO2 nanoparticles. HA+ 5 %TiO2 (1.40 ± 0.18 MPa.m1/2) and HA+ 8 %TiO2 (1.32 ± 0.18 MPa.m1/2) showed significantly higher fracture toughness values than HA (0.67 ± 0.09 MPa.m1/2). HA showed significantly higher characteristic stress (295.8 MPa) in comparison to groups with 5 % (235.1 MPa) and 8 % (214.4 MPa) TiO2 nanoparticles. Differences were not observed between the Weibull modulus values. The solubility results indicated that all experimental ceramics were above the 2000 ug/cm2 limit set by the ISO 6872:2015. SignificanceThis study proposed the development and characterization of a new ceramic for dental prosthesis made from HA extracted from bovine bones, with the intention of reusing these solids waste and transforming them into a sustainable and low-cost material. Although the experimental calcium phosphate ceramic with additions of 5 % and 8 % of TiO2 achieved desirable mechanical properties, the chemical solubility values were very high.

Surface modification of dental zirconia implants with a low infiltration temperature glass.

The glass infiltration technique was employed for surface modification of zirconia implants in this study. The prepared glass-infiltrated zirconia with low infiltrating temperature showed excellent mechanical properties and enough infiltrating layer. The zirconia substrate was pre-sintered at 1,200°C and the glass infiltration depth reached 400 μm after infiltrating at 1,200°C for 10 h. The infiltrating glass has good wetting ability, thermal expansion match and good chemical compatibility with the zirconia substrate. Indentation fracture toughness and flexural strength of the dense sintered glass-infiltrated zirconia composite are respectively 5.37±0.45 MPa•m1/2 and 841.03±89.31 MPa. Its elasticity modulus is 163.99±7.6 GPa and has about 500 μm infiltrating layer. The glass-infiltrated zirconia can be acid etched to a medium roughness (1.29±0.09 μm) with a flexural strength of 823.65±87.46 MPa, which promotes cell proliferation and has potential for dental implants.

Indentation response of multi-phase nanocrystalline NbWTi refractory multi-principal element alloy

NbWTi refractory multi-principal element alloy has been synthesized using powder metallurgy route. 40 h of mechanical alloying resulted in a single-phase alloy and subsequent spark plasma sintering transformed it into a multi-phase structure (1 BCC and 2 FCC phases). The alloy demonstrated an extremely high hardness of 12.29 ± 0.05 GPa at a load of 1000 g, along with excellent “density-normalized” hardness and indentation size effect. An indentation fracture toughness of 6.81 ± 0.16 MPa.m1/2 was measured using the cracks generated. Ultra-high absolute hardness, high “density-normalized” hardness and associated fracture toughness signifies the potential of this alloy for next generation structural engineering applications.

Zirconia toughened fluorosilicate glass-ceramics for dental prosthetic restorations

BackgroundDental glass-ceramics have limited strength and are unsuitable for high-stress-bearing areas. Zirconia stands out as a popular choice for reinforcing dental glass-ceramics due to its biocompatibility and high fracture toughness. ObjectivesThe objective of the study is to investigate the effect of an increase in zirconia (25, 30, 35 and 50 wt%) on microstructure, chemical solubility, hardness, fracture toughness, and brittleness index of fluorosilicate glass systems for dental restorative applications. Material and methodsThe fluorosilicate glass frit was obtained through the melt-quench technique. The glass frit was ball-milled with 25, 30, 35 and 50 wt % of 3 mol % yttria-stabilized zirconia (G-25Z, G-30Z, G-35Z, and G-50Z). The composites were sintered to 1000 °C for 48h at a heating rate of 5 °C/min. The glass frit was subject to differential scanning calorimetry. Phase analysis and microstructural characterization were carried out. The crystallite size of zirconia and glass-ceramics, micro-hardness, indentation fracture toughness, brittleness index, and chemical solubility were evaluated. ResultsPhase analysis reveals tetragonal and monoclinic zirconia with minor peaks of forsterite, fluorphlogopite, norbergite, and spinel. Their microstructures reveal the characteristic house-of-cards arrangement of fluorophlogopite crystals with dispersed zirconia. The results of hardness and fracture toughness show a statistically significant improvement with an increase in zirconia content. The crystallite size of zirconia and fluorophlogopite crystals with aspect ratio, brittleness index, and chemical solubility declined as the zirconia content increased. ConclusionsIncrease in zirconia content from 25 wt % to 50 wt % in heat-treated fluorosilicate glass systems reveals non-reactive zirconia with a stable glass matrix and limits the growth of fluorphlogopite crystals with a house-of-cards microstructure. This results in a range of properties suitable for dental restorations of enhanced hardness, and improved fracture toughness. Despite these improvements, the material maintains its machinability with reduced chemical solubility.