Zirconia Toughened Alumina Samples Research Articles

Microstructure, Mechanical and Thermal Properties of ZTA/Al2TiO5 Ceramic Composites

Zirconia-toughened alumina (ZTA)/Al2TiO5 composites were prepared via a sol–gel route. The prepared samples were uniaxially pressed and pressurelessly sintered at 1650–1700 °C for 1 h. The microstructure, densification, and X-ray diffraction patterns of the sintered ZTA/Al2TiO5 composites were investigated, and their mechanical properties, thermal coefficient, and shock resistance were characterized. The addition of Al2TiO5 hindered the grain growth of the alumina particles and enhanced the relative density, Vickers hardness, and bending strength of the composites compared with pure ZTA samples. The fracture toughness was improved by 19% upon the addition of 40 wt% Al2TiO5. Moreover, increasing the Al2TiO5 content resulted in an improvement in the thermal shock resistance.

Microwave sintering of zirconia toughened alumina - Influence of the type and content of doping in zirconia

This study focuses on the influence of zirconia on microwave (MW) sintering of zirconia-toughened alumina (ZTA). ZTA samples containing various zirconia powders (unstabilized and stabilized with yttria or ceria) were sintered in a MW cavity, in a sintering cell with or without susceptor. 8 mol% yttria-stabilized zirconia was denser when it was sintered without susceptor. The densification curves also showed different behaviours in the intermediate stage of sintering, between the four samples. The samples with 3 and 8 mol% yttria-stabilized zirconia were easier to densify than the samples with unstabilized and 10 mol% ceria-stabilized zirconia samples. This was confirmed when the samples were heated in a single-mode cavity. These differences of behaviour under MW can be linked to the chemical composition of zirconia. The substitution of zirconium cation by yttrium in the lattice generates an excess of oxygen vacancies and of dipoles. The latter are involved in the MW/material interactions.

Microstructure, mechanical properties, friction and wear performance, and cytotoxicity of additively manufactured zirconia-toughened alumina for dental applications

Zirconia-toughened alumina (ZTA) ceramic has potential dental restoration and repair applications due to its high mechanical strength, toughness, wear resistance, chemical durability, and biocompatibility. Nevertheless, there is a great deal of crack initiation caused by stress accumulation and also material wastage after computer-aided design/computer-aided manufacturing of ZTA ceramics in conventional clinical processing. In this study, we prepared a ZTA green compact using Stereolithography (SLA) technology followed by sintering at high temperatures ranging between 1450 °C and 1650 °C. The microstructures, mechanical properties, friction and wear performance, and cytotoxicity of the ZTA ceramic were investigated. The results indicate that all ZTA samples were composed of α-Al2O3, m-ZrO2, and t-ZrO2 phases before and after sintering. With increasing sintering temperatures from 1450 °C to 1650 °C, the density, mechanical properties, hardness, and wear performance of the ZTA samples were gradually improved. The ZTA sample sintered at 1650 °C with a relative density of 96.65% showed the best mechanical performance, with a flexural strength of 572.0 MPa, a Vickers hardness of 16.2 GPa, and a fracture toughness of 7.4 MPa m1/2. The sintered ZTA sample exhibited a good cell viability toward MC3T3-E1 cells.

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℃.

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.

Study and optimization of recast layer thickness and surface quality in laser trepan drilling of ZTA

Zirconia-toughened alumina (ZTA) has promising characteristics to be used for combustion chambers, pump, heat exchanger, armor, bearings, cutting tool inserts, aerospace, and nuclear parts. But it has limited applications due to its adverse machining characteristics. Laser machining has been proven to machine difficult-to-cut-materials with certain limitations. Being thermal energy–based advanced machining process, laser machining develops extreme thermal stresses and causes melting/vaporization. Therefore, ceramic samples are preheated at high temperature before applying laser machining. Control of laser machining quality without preheating of ZTA samples is a difficult task. The present paper investigates the laser trepan drilling (laser hole cutting) of 6.0-mm thick ZTA without preheating with the aim to optimize recast layer thickness, microcrack width on hole surface, and surface roughness. The optimal solution is determined by using a genetic algorithm. The results show an average improvement of approximately 15% in the above characteristics, considered simultaneously. The surface microcrack widths have been reduced much below than earlier claimed in laser processing of ceramics by other researchers. Mathematical relationship between input and output parameters has been developed and validated. The effect of process parameters on quality characteristics has also been discussed, scientifically.

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.

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.

In vitro antibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. Fourier transform infrared spectroscopy.

The metabolic response of Gram-positive Staphylococcus epidermidis (S. epidermidis) bacteria to bioceramic substrates was probed by means of Fourier transform infrared spectroscopy (FTIR). Oxide zirconia-toughened alumina (ZTA) and non-oxide silicon nitride (Si3N4) substrates were tested. Bacteria exposed to silica glass substrates were used as a control. S. epidermidis, a major cause of periprosthetic infections, was screened to obtain a precise time-lapse knowledge of its molecular composition and to mechanistically understand its interaction with different substrates. At the molecular level, the structure of proteins, lipids, nucleic acid, and aromatic amino acids evolved with time in response to different substrates. In combination with statistical validation and local pH measurements, a chemical lysis mechanism was spectroscopically observed in situ on the Si3N4 substrates. Utilization of FTIR in this study avoided fluorescence noise which occurred while probing the ZTA samples with Raman spectroscopy in a companion paper. The substrate-driven dynamics of polysaccharide and peptide variations in the bacterial cell wall, peculiar to Si3N4 bioceramics, are elucidated.

Development and characterization of zirconia–alumina composites for orthopedic implants

In this study, three different grades of alumina toughened zirconia composites (ATZ) (from 80 to 90wt% of zirconia), and three grades of zirconia toughened alumina (ZTA) from 80 to 90wt% of alumina were developed. Two types of stabilized zirconia were used: 3mol% yttria stabilized zirconia used on the ATZ, and 2mol% yttria stabilized zirconia for the ZTA. The composite powders were obtained by spray-drying with a controlled granulometric distribution. Uniaxial and cold isostatic pressing were performed. High density ceramics with densification above 97% were obtained after a low temperature sintering (1400°C) leading to enhanced mechanical properties. Higher values of fracture toughness and flexural strength were achieved for the ATZ samples (up to 5MPam1/2 and 1394MPa respectively), while ZTA samples presented higher values of hardness (up to 1846HV). Aging tests showed that ZTA samples did not present monoclinic zirconia after 96h. MTT and alkaline phosphatase activity assays were performed on the sintered samples. This study shows that ATZ and ZTA composites with good mechanical properties, aging resistance and osteoblastic cytocompatibility can be attained.

Analysis and optimization of dry sliding wear characteristics of zirconia reinforced alumina composites formed by conventional sintering using response surface method

An experimental investigation of the tribological performance during dry sliding wear was carried out on Zirconia Toughened Alumina (ZTA) ceramic composites. Process parameters for the analysis, such as the amount of Zirconia reinforcement added to alumina matrix, compaction pressure to form the green bodies of required shape and sintering temperature to make the final composite were selected as the control variables. The specific wear rate of ZTA against steel studied using a pin-on-disc method was selected as the response. The tribological experiments were carried out on all the 17 ZTA samples fabricated based on Box-Behnken design. The tribological test parameters such as a constant load of 49.05N (5kg) and sliding velocities of 0.3m/s for a sliding distance of 800m were kept constant. The regression model was developed for specific wear rate of dry sliding wear and the influential parameters were found to be sintering temperature and weight percentage of Zirconia added to alumina from Analysis of variance (ANOVA). The results concluded that decreasing the amount of Zirconia reinforcement into the alumina matrix and sintering temperature improves the specific wear rate. Also, the High resolution scanning electron microscopy (HR-SEM) analysis was done on the wear tracks to examine the wear mechanism involved. The optimization was done using Response Surface Method and a confirmation test was done to validate the optimized results.

Processing and Properties of Zirconia-Toughened Alumina Prepared by Gelcasting.

Zirconia-toughened alumina (ZTA) using yttria-stabilised zirconia is a good option for ceramic-ceramic bearing couples for hip joint replacement. Gelcasting is a colloidal processing technique capable of producing complex products with a range of dimensions and materials by a relatively low-cost production process. Using gelcasting, ZTA samples were prepared, optimising the stages of fabrication, including slurry preparation with varying solid loadings, moulding and de-moulding, drying and sintering. Density, hardness, fracture toughness, flexural strength and grain size were observed relative to slurry solid loadings between 58 and 62 vol. %, as well as sintering temperatures of 1550 °C and 1650 °C. Optimal conditions found were plastic mould, 4000 g/mol PEG with 30 vol. % concentration, 61% solid loading and Ts = 1550 °C. ZTA samples of high density (maximum 99.1%), high hardness (maximum 1902 HV), high fracture toughness (maximum 5.43 MPa m1/2) and high flexural strength (maximum 618 MPa) were successfully prepared by gelcasting and pressureless sintering.

Residual stress profiles in veneering ceramic on Y-TZP, alumina and ZTA frameworks: Measurement by hole-drilling

ObjectivesThe residual stress profile developed within the veneering ceramic during the manufacturing process is an important predicting factor in chipping failures, which constitute a well-known problem with yttria-tetragonal-zirconia polycrystal (Y-TZP) based restorations. The objectives of this study are to measure and to compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic framework materials: Y-TZP, alumina polycrystal (AL) and zirconia toughened alumina (ZTA). MethodsThe stress profile was measured with the hole-drilling method in bilayered disk samples of 19mm diameter with a 0.7mm thick Y-TZP, AL or ZTA framework and a 1.5mm thick layer of the corresponding veneering ceramic. ResultsThe AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6mm from the surface, and then becoming compressive again near the framework. SignificanceY-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Results support the hypothesis of the occurrence of structural changes within the Y-TZP surface in contact with the veneering ceramic to explain the presence of tensile stresses. Even if the presence of Y-TZP in the alumina matrix seems to negatively affect the residual stress profiles in ZTA samples in comparison with AL samples, the registered profiles remain positive in terms of veneer fracture resistance.

Quantitative analysis of the residual stress and dislocation density distributions around indentations in alumina and zirconia toughened alumina (ZTA) ceramics

Abstract Alumina, 10% and 20% ZTA with 1.5 mol% yttria stabiliser were subjected to Vickers indentation testing with loads from 1 to 20 kg. Cr3+ fluorescence and Raman spectroscopy were applied to the indent centre and around the indentation in order to investigate the origin of the signal, the effect of indentation loads and zirconia phase transformation on the residual stress and plastic deformation in the plastic zone. The results suggested that with very strong laser scattering, the depth resolution of ZTA materials was very poor, which lead to a very significant amount of the signal being collected from the subsurface regions below the plastic zone. It was also found that zirconia phase transformation reduced the compressive residual stress in the alumina matrix within the plastic zone, except at the indentation centre, due to the tensile residual microstress generated by the zirconia phase transformation. In addition, the dislocation density on the indent surface of the ZTA samples was significantly reduced due to the restriction of crack propagation and energy absorption during the phase transformation process. At the indent centre, the zirconia phase transformation was suppressed by the high compressive stress, therefore, no significant difference between alumina and ZTA in terms of their residual stress and dislocation density were observed. Using TEM observation, it was found that the plastic zone microstructure of pure alumina is different from that of ZTA, which is consistent with the Cr3+ fluorescence results.

Characterization of Zirconia-Toughened Alumina (ZTA) ceramics by SEM-cathodoluminescence

Cathodoluminescence (CL) studies in a scanning electron microscope of zirconia-toughened alumina (ZTA) with three different zirconia contents are described. The CL spectra show a broad violet emission centered at about 3.1 eV (400 nm) and a large and complex blue-green band centered near 2.6 eV (475 nm). The former arises from alumina, whereas the latter is associated with the zirconia component. A correlation between the luminescence and the nature of monoclinic to tetragonal zirconia is found. The results are discussed on the basis of oxygen vacancies and complex defects. The effects of toughening mechanisms on the luminescence of the ZTA samples are also considered.

Photoluminescent characterization of zirconia-toughened alumina (ZTA) ceramics

Photoluminescence (PL) investigations in zirconia-toughened alumina (ZTA) with three different zirconia contents were carried out. The PL emission spectra consist of a dominant structureless band centered at about 500 nm which exhibits a main excitation band centered near 292 nm with a subsidiary peak at about 254 nm. The 500 nm luminescence intensity is considerably increased by grinding. Luminescent intensities were plotted against zirconia content of ZTA samples. A good linear fit is found between the intensity ratio I-254/ I-292 and the total or tetragonal phase amount (wt%) of zirconia. After severe grinding, the ratio I-254/ I-292 tends to be independent of zirconia content. The results are analyzed on the basis of defect centres which would be favored by the tetragonal to monoclinic transformation.