Zirconia Toughened Alumina Composites Research Articles

Correlation between phase content and mechanical properties of SiCw- ZTA composites sintered by SPS

The zirconia toughened alumina (ZTA) composites have been widely used as an engineering material in many application areas due to their remarkable mechanical properties. However, the fracture toughness of ZTA does not generally meet the requirements of aerospace, machinery and other fields. In this study, the SiC whiskers (SiCw) have been incorporated in the ZTA composites to improve the fracture toughness. The SiCw employed in this study mainly consist of the β phase, with a small fraction of the α phase. The effect of the SiCw content and sintering temperature on the microstructure and mechanical properties of the SiCw-ZTA (ZASw) composites has been systematically studied. The incorporation of SiCw is noted to reduce the density of the ZASw composites. On enhancing the SiCw content, the Vickers hardness and fracture toughness of the composites initially decrease, followed by an increase. However, the flexural strength of the composites increases with the SiCw content. At a SiCw content of 10.0 vol %, the strength, hardness and toughness are observed to reach the maximum values. On enhancing the sintering temperature, the strength and hardness of the composites are observed to remain nearly constant, while the toughness of the composites is increased.

Effect of Graphene-Oxide Addition on the Microstructure and Mechanical Properties of Two-Stage Sintered Zirconia-Toughened Alumina (ZTA) Composites

United Nations has estimated that 130 million people would suffer from osteoarthritis worldwide by 2050. This disease would require patients to undergo a surgery known as Total Hip Replacement (THR) which has a failure rate of approximately 1 % with a lifespan of 20 years. The biomaterials used to manufacture this total hip artroplasty are mainly made of Zirconia-Toughened Alumina. In this work, Zirconia Toughened Alumina (ZTA) composites with 10 vol% Y-TZP content were doped with small amount (0.01 to 1 wt%) of graphene oxide (GO). The GO-doped ZTA composites were produced via two-stage sintering with T1 ranging between 1400°C and 1550°C, heating rate of 20°C/min, followed by T2 of 1350°C and 12 hours holding time. The sintered ZTA samples were then evaluated on its microstructure and mechanical properties such as bulk density, Vickers hardness, Young’s modulus and fracture toughness to investigate the effect of GO addition on ZTA samples prepared via two-stage sintering. The results showed that ZTA composites containing up 0.1 wt% GO is beneficial in improving the microstructural and mechanical properties of ZTA composites prepared via two-stage sintering. The sample recorded a high hardness of up to 18.5 GPa, Young’s modulus of 406 GPa and fracture toughness of 5.8 MPam1/2 when sintered at T1 of 1450℃.

Critical load and wear regime of hydrothermal-aged SrO-doped ZTA composite

The research work has demonstrated the effect of hydrothermal ageing ([Formula: see text]C, 40 h, 1.034 bar) on friction and wear behavior of SrO-doped zirconia toughened alumina (ZTA) composite. Surface topography and wear regime behavior are established in the perspective of ageing time, load, phase transformation and toughening phenomena. The estimated critical load is confirming the expedition of mild to severe wear in the presence of microcrack formation during adhesive and abrasive wear between SrO-doped ZTA (disc) and ZrO2 (ball) tribo couples, where adhesion between the SrO–ZTA disc and ZrO2 ball results in transfer of ZrO2 particles from ball to disc. Roughness parameters ([Formula: see text], [Formula: see text]) are elucidated to understand the influence of load and ageing conditions, as well as the in vitro bioactivity of sintered specimens is assessed in simulative body fluid (SBF) solution.

Microstructural, mechanical, and optical characterization of an experimental aging-resistant zirconia-toughened alumina (ZTA) composite

ObjectiveTo evaluate the effect of aging on the microstructural, mechanical, and optical properties of an experimental zirconia-toughened alumina composite with 80%Al2O3 and 20%ZrO2 (ZTA Zpex) compared to a translucent zirconia (Zpex) and Alumina. MethodsDisc-shaped specimens were obtained by uniaxial and isostatic pressing the synthesized powders (n = 70/material). After sintering and polishing, half of the specimens underwent aging (20 h, 134 °C, 2.2 bar). Crystalline content and microstructure were evaluated using X-ray diffraction and scanning electron microscopy, respectively. Specimens underwent biaxial flexural strength testing to determine the characteristic stress, Weibull modulus, and reliability. Translucency parameter (TP) and Contrast ratio (CR) were calculated to characterize optical properties. ResultsZTA Zpex demonstrated a compact surface with a uniform dispersion of zirconia particles within the alumina matrix, and typical alumina and zirconia crystalline content. ZTA Zpex and alumina exhibited higher CR and lower TP than Zpex. ZTA Zpex and Zpex showed significantly higher characteristic stress relative to alumina. While aging did not affect optical and mechanical properties of ZTA Zpex and alumina, Zpex demonstrated a significant increase in translucency, as well as a in characteristic stress. Alumina reliability was significantly lower than others at 300 MPa, ZTA Zpex and Zpex reliability decreased at 800 MPa, except for aged Zpex. SignificanceWhile aging did not affect the mechanical nor the optical properties of ZTA Zpex and alumina, it did alter both properties of Zpex. The results encourage further investigations to engineer ZTA as a framework material for long span fixed dental prostheses specially where darkened substrates, such as titanium implant abutments or endodontically treated teeth, demand masking.

Two-Stage Sintering of Nb<sub>2</sub>O<sub>5</sub> Doped Zirconia Toughened Alumina (ZTA) Composites

It is estimated that 130 million people will suffer from osteoarthritis by 2050 which require patient to undergo a surgical procedure known as total hip replacement which has lifespan of 20 years and failure rates of ~1%. This research would highlight the effects of doping Niobium Oxide (Nb2O5) between 0 vol % to 0.8 vol % into Zirconia-Toughened Alumina (ZTA) composites which is the main biomaterials used to manufacture total hip arthroplasty. The samples were sintered using two-stage sintering (TSS) between 1400°C and 1550°C for first-stage sintering temperature at heating rate of 20°C/min. At second stage, the samples were sintered at 1350°C and hold for 12 hours. It was found that TSS combined with addition of Nb2O5 as dopants were beneficial in producing fine-grained ZTA composites with improved mechanical properties compared to undoped ZTA composites produced via TSS. Compared to undoped ZTA composites, samples doped with Nb2O5 and sintered at T1 ≥1400°C were fully densed (>98%), achieved Vickers hardness more than 20 GPa and Young’s modulus higher than 410 GPa and at the same time fracture toughness of more than 8 MPam1/2. Based on the findings, production of ZTA composites with enhanced mechanical properties with longer lifespan is possible which is beneficial in ensuring the well-being of osteoarthritis patients.

The Effect of Ta<sub>2</sub>O<sub>5</sub> on the Densification Behaviour and Mechanical Properties of Zirconia-Toughened Alumina (ZTA) Composites Prepared by Two-Stage Sintering

By 2050, 130 million people are estimated to suffer from osteoarthritis worldwide which would require patients to undergo total hip replacement procedure which have a lifespan of 20 years and failure rates of ~1%. In this research, Zirconia Toughened Alumina (ZTA) which is the main biomaterial used for total hip arthroplasty were doped with varying vol % of Tantalum Oxide (Ta2O5) from 0 to 0.4 vol % were produced through conventional two-stage sintering with first stage sintering temperature, ranging between 1400°C and 1550°C, heated at 20°C/min, followed by second stage sintering temperature of 1350°C and hold for 12 hours. The efficacy of two-stage sintering on the microstructure and mechanical properties of the sintered samples were then evaluated. Addition of Ta2O5 combined with two-stage sintering were able to produce ZTA composites with enhanced grain size and mechanical properties compared to undoped ZTA composites. The samples with 0.3 vol% Ta2O5 content and above sintered at T1 ≥1450°C achieved density > 99% T.D., Vickers hardness > 19 GPa, Young’s modulus > 400 GPa and fracture toughness > 6 MPam1/2 when compared to undoped ZTA composites. This would enable production of ZTA with improved mechanical properties and lifespan ensuring the well-being of people suffering from osteoarthritis.

Aging resistant ZTA composite for dental applications: Microstructural, optical and mechanical characterization

ObjectiveTo synthesize a zirconia toughened alumina (ZTA) composite with 70% alumina reinforced by 30% zirconia for dental applications and to characterize its microstructure and optical properties for comparison with the isolated counterpart materials and a first-generation 3Y-TZP. MethodsDisc-shaped specimens were divided in four groups (n = 70/material): (1) 3YSB-E (first generation 3Y-TZP), (2) Zpex (second generation 3Y-TZP), (3) alumina, and (4) ZTA-Zpex 70/30. After synthesis, ceramic powders were pressed, and green-body samples sintered following a predetermined protocol. Specimens were polished to obtain a mirror surface finish. Apparent density was measured by Archimedes principle. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the crystalline content and microstructure. Reflectance tests were performed to determine the contrast-ratio (CR) and translucency-parameter (TP). Mechanical properties were assessed by biaxial flexural strength (BFS) test. All analyses were conducted before and after artificial aging (20 h, 134 °C, 2.2 bar). Optical parameters were evaluated through repeated-measures analysis of variance and Tukey tests (p < 0.05). BFS data were analyzed using Weibull statistics (95% CI). ResultsHigh density values (95–99%) were found for all ceramic materials and SEM images exhibited a dense microstructure. While XRD patterns revealed the preservation of crystalline content in the ZTA composite, an increase in the monoclinic peak was observed for pure zirconias after aging. Significantly higher CR and lower TP values were observed for the ZTA composite, followed by alumina, 3YSB-E, and Zpex. The highest characteristic stress was recorded for 3YSB-E, followed by intermediate values between ZTA and Zpex, and the lowest for alumina. Aging affected the optical and mechanical properties of both zirconias, while remained stable for ZTA composite and alumina. SignificanceThe synthesis of experimental 70−30% ZTA composite was successful and its relevance for dental applications relies on its higher masking ability, aging resistance, and strength similar to zirconia.

Mechanical and Tribological Properties of Alumina Toughened Zirconia Composites through Conventional Sintering and Microwave Sintering

The present study investigates the relative density, mechanical and tribological properties of 3 mol% yttria-stabilized zirconia composites reinforced with 10 vol% of alumna through both conventional sintering and microwave sintering (CS and MW). The variations in mechanical and tribological properties were correlated to the corresponding microstructures. Wear tests were carried out on the composite samples against EN30 grade stainless steel disk with 320-grade emery paper for a sliding distance of 1500 m under dry sliding condition. Wear rate and coefficient of friction of the developed composite were evaluated with varying normal loads in the range of 20–200 N with corresponding sliding velocities of 0.79 m/s, 1.4 m/s, 1.8 m/s and 2.4 m/s, respectively. The maximum value of wear rate and COF of the MW samples were 51.21% and 24.59%, respectively, which were lower compared to that of CS.

Aging resistance of an experimental zirconia-toughened alumina composite for large span dental prostheses: Optical and mechanical characterization

PurposeTo synthesize a zirconia-toughened alumina (ZTA) composite with 85% alumina matrix reinforced by 15% zirconia and to characterize its optical and mechanical properties before and after artificial aging, to be compared with a conventional dental zirconia (3Y-TZP). Material and methodsAfter syntheses, ZTA and 3Y-TZP powders were uniaxially and isostatically pressed. Green-body samples were sintered and polished to obtain 80 disc-shaped specimens per group (12 × 1 mm, ISO 6872:2015). The crystalline content and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Optical properties were determined by the calculation of contrast ratio (CR) and translucency parameter (TP) using reflectance data. Mechanical properties were assessed by Vickers hardness, fracture toughness and biaxial flexural strength test (BFS). All analyses were conducted before and after artificial aging (20h, 134 °C, 0.22 MPa). Optical parameters and microhardness differences were evaluated through repeated-measures analysis of variance (p < 0.05). BFS data were analyzed using Weibull statistics (95% CI). ResultsThe synthesis of the experimental ZTA composite was successful, with 98% of theoretical density, as shown in the SEM images. XRD patterns revealed typical zirconia and alumina crystalline phases. ZTA optical properties parameters showed no effect of aging, with a high CR and low TP values denoting a high masking-ability. 3Y-TZP presented lower masking-ability and aging significantly affected its optical properties. ZTA Vickers hardness, fracture toughness and Weibull parameters, including characteristic stress and Weibull modulus were not influenced by aging, while 3Y-TZP presented a significant decrease in characteristic stress and increase in fracture toughness after aging. The ZTA probability of survival for missions of 300 and 500 MPa was estimated at ~99% validating its use for 3-unit posterior fixed dental prostheses (FDP), and no different from conventional 3Y-TZP. At high-stress mission (800 MPa) a significant decrease in probability of survival was observed for aged 3Y-TZP (84%) and for immediate and aged ZTA (73 and 82% respectively). ConclusionThe ZTA composite presented a dense microstructure, with preservation of the crystalline content, optical and mechanical properties after artificial aging, which encourages future research to validate its potential use for large span FDP.

Grain growth suppression of ZTA by multi-step sintering

Effect of two-step sintering of Zirconia Toughened Alumina (ZTA) on microstructure and mechanical properties were studied in the present work. Al2O3 and 3YSZ nanoparticles were mixed by high speed vibrating mill, and powders were compacted by a uniaxial pressing protocol at 150 MPa, and sintered through both conventional sintering schedule (CSS) and two-step sintering (TSS) schedules. The composition containing 95 wt% Al2O3 and 5 wt% 3YSZ sintered at two-step sintering (TSS-2; 1600 °C/10 min followed by 1500 °C/6 h) exhibits higher Vickers hardness (1835 HV), fracture toughness (4.95 ± 0.1 MPa.√m), compressive strength (900 MPa) and Diametral tensile strength (125 MPa), respectively. The ZTA composite shows relative density 99.2% with grain size 4.5 µm during CSS at 1600 °C for 4 h. However, the TSS-2 facilitates to achieve relative density 98.4% consist of 1.4 µm alumina grain size that eventually experiences ∼21% fracture toughness increment through zirconia phase assisted transformation toughening.

Effect of grain size and amount of zirconia on the physical and mechanical properties and the wear resistance of zirconia-toughened alumina

The effects of the ZrO2 content and the particle size of ZrO2 powders on the microstructure, phase composition, physical and mechanical properties, and the abrasion wear resistance of advanced Al2O3 ceramics and zirconia-toughened alumina (ZTA) composites containing 0 to 30 mass% yttria-stabilised zirconia (YSZ) were investigated. The composite with a ZTA content of 30 mass% of ZrO2 exhibited the greatest resistance to abrasion wear. α-Al2O3 reflex broadening (hkl = 113) as a result of the microstresses in the Al2O3 crystal lattice during sandblasting decreased with increasing ZrO2 amount, where the ZrO2 particles located along the grain boundaries of Al2O3, hindering their growth and deformation. The use of nanodispersed ZrO2 powder produced by the plasma chemical technique led to a 1.5-fold increase in wear resistance in the resultant ZTA ceramic.

Development and evaluation of Al2O3–ZrO2 composite processed by digital light 3D printing

Digital Light Processing (DLP) is a promising approach to fabricate delicate ceramic components with high-fidelity structural features. In this work, the alumina and zirconia/alumina ceramic suspensions with low viscosity and high solid loading (40 vol%) were prepared specifically for DLP 3D printing. After debinding and sintering, the final parts were obtained without any defects. The surface morphologies and mechanical properties of alumina (Al2O3) and zirconia toughened alumina (ZTA) composites were investigated and the results showed that the final parts exhibited high relative densities and good interlayer combination at the sintering temperature of 1600 °C. Comparing with the Al2O3, the ZTA composites exhibited significantly enhanced density (99.4%), bending strength (516.7 MPa) and indentation fracture toughness (7.76 MPa m1/2).

Interplay between internal stresses and matrix stiffness influences hydrothermal ageing behaviour of zirconia-toughened-alumina

Zirconia based bio-ceramics such as ZTA (zirconia-toughened alumina) composite are often used in orthopaedic and dental implants. The hydrothermal ageing behaviour of zirconia in humid environments is an important factor affecting the lifetime of these biomaterials. It is a tetragonal-to-monoclinic phase transformation that has been shown to be both temperature- and stress-dependant. Here, ZTA composites with zirconia inclusion particles of different sizes were prepared. The influence of zirconia inclusions on internal stresses and thus on ageing behaviour was studied by Raman micro-spectroscopy and X-ray diffraction. The results show that the ageing kinetics result from a balance between stiffer matrix and increased tensile stress in the zirconia inclusion as the local alumina fraction increase. As a result, the maximum monoclinic fraction formed after 1200 h ageing at 134 °C decreases with increasing alumina content, showing the predominance of the stabilization of tetragonal particles by a stiff matrix over their de-stabilization by tensile stress.

Effect of MgO Addition on the Mechanical and Dynamic Properties of Zirconia Toughened Alumina (ZTA) Ceramics.

Zirconia toughened alumina (ZTA) is a promising advanced ceramic material for a wide range of applications that are subjected to dynamic loading. Therefore, the investigation of dynamic compressive strength, fracture toughness and hardness is essential for ZTA ceramics. However, the relationship between these mechanical properties in ZTA has not yet been established. An example of this relationship is demonstrated using ZTA samples added with MgO prepared through conventional sintering. The microstructure and mechanical properties of ZTA composites were characterized. The hardness of ZTA composites increased for ≤0.7 wt.% MgO due to the pinning effect of MgO and decrease of the porosity in the microstructure. Oppositely, the fracture toughness of ZTA composites continuously decreased due to the size reduction of Al2O3 grains. This is the main reason of deteriorate of dynamic compressive strength more than 0.2 wt.% of MgO addition. Therefore, the SHPB test shows the improvement of the dynamic compressive strength only up to a tiny amount (0.2 wt.% of MgO addition) into ZTA ceramics.

Thermal decomposition of polyhydroxy processing agents dedicated to colloidal shaping of ceramics – Thermogravimetry coupled with mass spectrometry and properties of ZTA composites

The paper presents the thermal decomposition of the new, highly efficient organic additives used in colloidal shaping of ceramics, that is lactobionic acid (LAc), galacturonic acid (GAc) and diglyceryl acrylate (DGA). The sugar acids are effective deflocculants, especially for nanopowders, while DGA is the new monomer dedicated to gelcasting process. Most organic additives are indispensable in shaping step but must be then eliminated in order to obtain pure ceramic phase. The DTA/TG measurements coupled with mass spectrometry allowed to determine the thermal decomposition of organic compounds and observe type of gasses released to the atmosphere during heating. Additionally, the influence of the analyzed substances on the properties of selected ceramic suspensions and sintered bodies has been discussed. The new compounds have been examined in the preparation of ZTA (zirconia toughened alumina) composites by gelcasting, slip casting and subsequent sintering. The rheological behaviour of Al2O3-ZrO2 suspensions as well as selected properties (Vickers hardness, fracture toughness and microstructure) of sintered ZTA samples are presented.

Effect of Alumina Nanofibers Content on the Microstructure and Properties of ATZ Composites Fabricated by Spark Plasma Sintering

In this work, 3mol.% yttria-stabilized zirconia was used as a matrix for the fabrication of alumina toughened zirconia (ATZ) composites. Alumina nanofibers were reinforcing additives with an amount of 1, 5 and 10wt.%. Fully dense ATZ composites were obtained by spark plasma sintering. Microstructure observations of the composites showed the mixed fracture mode, which favorably affects the fracture toughness. It is shown that the fracture toughness and Vickers microhardness of ATZ composites were significantly improved by the addition of Al2O3 nanofibers compared with monolithic ZrO2. The fracture toughness of composite with 1wt.% nanofibers addition is 4.40MPa·m1/2. The microhardness of composite with 5wt.% nanofibers is 16.75GPa. The toughening and strengthening mechanisms were analyzed.

Effect of carbon nanotubes reinforcement on the mechanical properties of alumina and ZTA composites for ballistic application

Abstract Toughened and hardened alumina/carbon nanotubes and zirconia-toughened alumina (ZTA)/carbon nanotubes nanocomposites were developed by conventional ceramics route using pressureless sintering for the ballistic application. The multiwall carbon nanotubes (CNT) were functionalized with nitric acid oxidation reaction. Moreover, the surfactants sodium dodecyl sulphate and gum arabic were used to promote a homogeneous distribution of CNT in the ceramic matrix. Ceramic powders were prepared with pure alumina, alumina with the addition of 20 wt% of tetragonal zirconia/yttria, alumina/CNT and ZTA/CNT with the addition of 0.1 and 0.5 wt% of CNT. The morphology of nanocomposites was characterized by SEM-FEG. The mechanical properties of sintered samples were evaluated by flexural bending, Vickers microhardness and fracture toughness by SEVNB method. The addition of CNT in the ceramic and composite caused a general increase in densification, hardness, flexural strength and fracture toughness. ZTA composite with the addition of 0.1 wt% of CNT yielded the best results.

Tougher and harder zirconia toughened alumina (ZTA) composites through in situ microstructural formation of LaMgAl11O19

Advanced ceramic materials are highly demanded for various modern industrial and practical engineering applications. Nonetheless, the requirement of attainment hard and simultaneously tough materials is a crucial matter for industrial sectors. To accomplish this target, the strategy of designing a novel microstructure of Zirconia Toughened Alumina (ZTA) ceramics was utilised through in situ formation of LaMgAl11O19 (LMA) based on the stoichiometry ratio of constitute oxides inside ZTA composites during sintering process. ZTA Samples were conventionally sintered at 1600 °C for 2 h to ensure fully formation of LMA while their characteristics were analysed using SEM-EDX and XRD. The LMA elongated grains significantly enhanced ZTAs' Indentation Fracture Resistance (KIFR) due to crack deflection and crack bridging mechanisms combined with transgranular and intergranular fracture modes. Additionally, higher hardness was obtained due to high LMA density, creation of low porous ZTA and strong interface bonding between LMA and ZTA grains. The KIFR was stable while the hardness was steadily declined due to more porosity accompanied by LMA in situ formation. Consequently, sustainable high hardness and enhanced KIFR of ZTA ceramics were achieved. The optimum outcomes were superior KIFR (7.8 MPa.m^1/2) and hardness (1660 HV) than the pure ZTA (5.9 MPa.m^1/2, 1568 HV). The investigation provides a new hint for future design and fabrication of economic and high performance ceramics through in situ formation of LMA according to the stoichiometric ratio of the reinforcing oxides.

Sintering of carbon nanotube-reinforced zirconia-toughened alumina composites prepared by uniaxial pressing and cold isostatic pressing

The effect of carbon nanotubes (CNTs) on hardness and fracture toughness in CNT-reinforced zirconia-toughened alumina (ZTA) composites prepared by uniaxial pressing (UP), cold isostatic pressing (CIP), and pressureless sintering (PLS) at 1520 °C in air during 1 h was investigated. Both pressing methods yielded nearly identical relative densities higher than 93%. The Vickers microhardness was increased in the composites treated by CIP, whereas the fracture toughness was decreased for the CIPed composites. This could be associated with the fracture mode and the toughening mechanisms present in the microstructure. CIPed ZTA composites with additions of 0.01 wt% MWCNTs obtained an increase in hardness of 26% and a decrease of 8% in fracture toughness compared to uniaxially pressed ones. From all studied composites, those with additions of MWCNTs yielded the better mechanical properties in comparison to composites with additions of SWCNTs, suggesting that MWCNTs are more easily dispersed into the ceramic matrix, thereby producing improvements as reinforcement agents.

Effect of Ta2O5 addition on the microstructure and mechanical properties of TiO2-added yttria-stabilized zirconia-toughened alumina (ZTA) composites

In this study, the effect of Ta2O5 addition on the phase evolution and mechanical properties of sintered (1600 °C, 4 h) TiO2-added yttria-stabilized zirconia-toughened alumina (ZTA) ceramic composites was investigated. The scanning electron microscopy and X-ray diffraction results revealed the formation of a new tantalum zirconium oxide, TaZr2.75O8, with a block-like morphology at Ta2O5 contents higher than 1 wt%. The grain sizes of both the Al2O3 and yttria-stabilized zirconia phases first increased and then decreased with an increase in the Ta2O5 content. The relative density, Vickers hardness, and fracture toughness of the composites were found to be strongly dependent on their grain sizes, relative densities, and the formation of the TaZr2.75O8 secondary phases. The composite with 3 wt% Ta2O5 showed the highest relative density (99.3%), Vickers hardness (1932 HV), and fracture toughness (8.21 MPa m1/2).