Zirconia Toughened Alumina Composites Research Articles

Early Biological Response to Poly(ε-Caprolactone)/Alumina-Toughened Zirconia Composites Obtained by 3D Printing for Peri-Implant Application.

The improvement of the mucosal sealing around the implant represents a challenge, one that prompted research into novel materials. To this purpose, a printable poly(ε-caprolactone) (PCL)-based composite loaded with alumina-toughened zirconia (ATZ) at increasing rates of 10, 20, and 40 wt.% was prepared, using a solvent casting method with chloroform. Disks were produced by 3D printing; surface roughness, free energy and optical contact angle were measured. Oral fibroblasts (PF) and epithelial cell (SG) tests were utilized to determine the biocompatibility of the materials through cell viability assay and adhesion and spreading evaluations. The highest level of ATZ resulted in an increase in the average roughness (Sa), while the maximum height (Sz) was higher for all composites than that of the unmixed PCL, regardless of their ATZ content. Surface free energy was significantly lower on PCL/ATZ 80/20 and PCL/ATZ 60/40, compared to PCL and PCL/ATZ 90/10. The contact angle was inversely related to the quantity of ATZ in the material. PF grew without variations among the different specimens at 1 and 3 days. After 7 days, PF grew significantly less on PCL/ATZ 60/40 and PCL/ATZ 80/20 compared to unmixed PCL and PCL 90/10. Conversely, ATZ affected and improved the growth of SG. By increasing the filler amount, PF cell adhesion and spreading augmented, while PCL/ATZ 80/20 was the best for SG adhesion. Overall, PCL/ATZ 80/20 emerged as the best composite for both cell types; hence, it is a promising candidate for the manufacture of custom made transmucosal dental implant components.

Mechanical evaluation of DIW-printed carbon nanofibers - alumina-toughened zirconia composites

Direct ink writing (DIW) offers cost-effective fabrication of intricate ceramic structures. However, the mechanical properties (reliability) of DIW-obtained components have been inadequate for structural applications. This study aimed to improve mechanical properties of DIW alumina-toughened zirconia (ATZ) composite filaments with and without carbon nanofibers (CNFs). Optimized debinding and sintering conditions were determined for Conventional Sintering (CS) and Spark Plasma Sintering (SPS). The influence of nozzle diameter, CNF content and sintering method on the fracture strain, Young’s modulus, flexural strength and Weibull modulus was carefully assessed via correlation analyses. CNFs, although intended to enhance properties, were often agglomerated, which negatively affected mechanical properties. Smaller nozzle diameters enhanced Young’s modulus, with CS-sintered ATZ filaments showing transformation-induced plasticity (TRIP). Mechanical properties rivaled or surpassed those of conventional techniques (e.g., cold isostatic pressing, slip casting) with a good level of mechanical reliability achieved. Overall, DIW showed promise for ceramic materials, particularly ductile Ce-TZP-based composites.

Effect of β-spodumene additions on the phase composition, thermal, mechanical, and fracture behavior of zirconia toughened alumina composites

The fabrication of ceramic composites with low thermal expansion and excellent mechanical properties is essential for thermal barrier coating (TBC) applications. For this purpose, using the sol-gel process, novel ceramic composites were developed by combining varying weight percentages of β-spodumene (0–20 wt%) with zirconia toughened alumina (ZTA). The influence of β-spodumene addition on the densification, phase composition, microstructure, and mechanical, thermal, and fracture behavior of the studied composites was investigated experimentally and numerically. Increasing the β-spodumene content reduces the sintering temperature of the formed composites by 75 °C. Introducing 5 wt% β-spodumene to ZTA composite improves the densification process by serving as a mineralizer. X-ray diffraction (XRD) revealed that the t-m ZrO2 transformation was enhanced by increasing the β-spodumene content. The results demonstrated that composites with β-spodumene content of 5 wt% exhibited the best mechanical performance. The numerical prediction of fracture toughness agreed well with the experimental results for different composites.

The Influence of the Phase Arrangement of ATZ Composites on Their Wear Rate Under Ball-on-Disc Tests

An alumina-toughened zirconia (ATZ) material, fabricated using a procedure consisting of the common sintering of two different zirconia powders, was tested using the ball-on-disc method in a temperature range between 20 and 400 °C. Tetragonal zirconia balls were used as a counterpart. Three different types of microstructure were designed, one consisting in separated alumina inclusions in zirconia matrix, the second one containing alumina inclusion in the amount close to the percolation point and another one which was a combination of two continuous phases, penetrating the whole volume of the composite. It was detected that at elevated temperatures all materials showed distinct decrease of measured wear rate. Composite with a low alumina content showed minimal wear rate at 300 °C and composites with higher amount of alumina were the most wear resistant at 400 °C. There are some evidences that this minimal wear rate is connected with a pseudoplastic behavior of a layer formed between co operating elements of tribological pair.

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.

ATZ composites with enhanced mechanical reliability and lifetime

Tetragonal zirconia demonstrates very good mechanical properties in rapid tests but reveals the strength decrease over time typical for oxide materials. If the material is loaded for a long period of time, the subcritical crack propagation occurs. Introducing additional phases into the zirconia matrix can both limit the grain size growth and introduce residual stresses, which can retard or even stop the crack run. The base of this work is a composite from the family of alumina toughened zirconia (ATZ) ones with a dispersed small content of alumina (1.5 wt%). The matrix was obtained via common sintering of different zirconia powders with various yttria content, which resulted in the material of a very small grain size. Incorporating additional alumina (8.4 or 15.8 wt%) led to the independence of strength from the loading time. Other calculations were made in order to estimate the survival time of the material working under load.

Effect of milling time on the mechanical properties of zirconia toughened alumina composites

Due to high reliability, longer useful life and sustainability in harsh environment, zirconia toughened alumina (ZTA) are prominent composite used by multifarious industries. In general, the components of ZTA are fabricated through powder metallurgy route consisting of various steps like milling, compaction, sintering, post polishing etc. Every step has propounded its dire effect on the mechanical properties. A lot of investigations are dedicated on thermal effect, but very little research is available on the milling of powders before densification. Therefore, this study discloses the effect of milling time on the bulk density, hardness and fracture toughness of ZTA composite. Co-precipitation process is opted to fabricate the ZTA composites. The synthesized ZTA composites are milled for five different time period i.e. 30, 60, 90, 120 and 150 min. A significant effect of milling time is observed on the mechanical properties. In case of, bulk density an improvement is noticed upto the optimal grain size. Beyond that the bulk density decreases, due to the inferior compaction resulting in high porosity inside the matrix. The evaluated value of hardness resembles same trend of bulk density due to direct relationship. The fracture toughness shows continuous increment with increase in milling time, but significantly improvement is noticed at high milling time. The said result may be attributed to the presence of high porosity inside the cluster of composite.

Tribology and in-vitro biological characterization of TiO2 addition on ceria stabilized zirconia-toughened alumina (CSZTA) composite

ABSTRACT The effect of TiO2 addition on tribology and in-vitro biological characteristics of ceria-stabilized zirconia-toughened alumina (CSZTA-TiO2) ceramic composites were examined and presented in this study. Through the powder metallurgy route, the TiO2 added to CSZTA samples were synthesized and sintered (air environment). Additionally, the pin on the disc machine was used to examine the wear characteristics of sintered samples. Adding TiO2 to CSZTA enhances the tribological properties compared to pure ceria-stabilized zirconia-toughened alumina (CSZTA). In addition, the samples (CSZTA and CSZTA-TiO2) were subjected to aging. There is no monoclinic-phase transformation (no degradation) in the CSZTA-TiO2 sample after 100 h of testing, confirming its great resistance to LTD. The bioactivity of developed CSZTA and CSZTA-TiO2 samples was studied using simulated body fluid (SBF). After chemical treatment, it was shown that the composite would create an apatite layer that resembled bone when soaked in a simulated body fluid with ion concentrations equal to human blood plasma. These results suggest that it may generate apatite within a live organism and connect to the bone via the apatite layer.

Direct ink writing of ATZ composites based on inks prepared by colloidal or hydrogel route: Linking inks rheology with mechanical properties

The Direct Ink Writing (DIW) technique stands out due to its fast processing, low amounts of additives demanded for the ink’s preparation and, consequently, the relatively quickly thermal post-processing cycles. On this behalf, the development of inks for DIW is usually based on colloidal or hydrogel-based processing routes, which derive from interparticle interactions or gel-particle interactions, respectively. The aim of this work was to evaluate the impact of colloidal or hydrogel-based ceramic inks processing routes in the properties of Alumina Toughened Zirconia (ATZ) composites prepared by DIW. It was found that the alumina grains were homogeneously dispersed into the zirconia matrix on samples derived from the colloidal ink, while big agglomerates could be found on those derived from the hydrogel ink. The good homogeneity observed on the colloidal route is related with the particle-particle (electrosteric) stabilization mechanism that induced an efficient dispersion of the starting powders, in contrast with the hydrogel route where the steric stabilization mechanism is dominant. Given the high interest of these composites as biomaterials, the achievements here attained open future opportunities for the near-net-shape processing of geometrically complex and customized dense and tough prosthesis and implants by DIW with mechanical performance comparable with conventional processing routes.

Effect of Adding MgO on Microstructure of Zirconia Toughened Alumina (ZTA) Composite for Medical Applications

Zirconia toughened alumina (Biolox delta) is a new-generation ceramic with four times the strength of alumina alone, used in artificial joints. The composite ZTA, consisting of 82 wt. %Al2O3, 17 wt. % ZrO2, 0.5 wt. % Cr2O3, and 0.5 wt. % SrO, was made using the sol-gel process, starting with salts. To investigate the effects of MgO on the ZTA microstructure, two concentrations (0.25 and 0.5 wt. %) of MgO were added to biolox during gelation to study the ZTA microstructure. Powders were sintered in the air for 2 hrs. at 1450 ºC. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray analysis (EDX) were used to characterize sintering powders. ZTA + xMgO structural characteristics differ from pure ZTA's. According to XRD calculations, grainsize decreased from 41.82 nm to 31.88 and 26.83 nm with increasing MgO concentration, but the specific surface area (SSA) increased from 40.63 to 54.79 m2/gm while crystallization improved. SEM examination shows the composite has a homogeneous dispersion of shaped particles. The EDX test shows the composite's homogeneous element distribution. ZTA+ xMgO powders were more antibacterial than ZTA powders. MgO inhibits bacterial activity and grain formation in ZTA composite during sintering, which makes it a good choice for medical applications, mainly artificial joints.

Reviewing Alumina-Zirconia Composite as a Ceramic Biomaterial

In orthopedics, increasing the implant lifetime minimizes the need for repair surgery, which benefits the patient’s health and the practice bottom line. The quality of the materials and designs is always being enhanced to reach the ultimate objective of a single implant that would last a person their whole life. The purpose of orthopedic treatments is to enhance the patient’s ability to participate in normal activities and socialize, and the implant carrier should not be subjected to unnecessary limitations. As a result, implants are exposed to severe mechanical stress and the inherently hostile in vivo biochemical environment, which is particularly prevalent in younger and more active people. The development of hip prosthesis design and materials has taken this path in recent years. This development is one of the most challenging problems in the field of implant technology in this century. In this study, various materials, including ceramics, glass, metal alloys, polymers, metal alloys, composites, and others, were used in an effort to combine biocompatibility with fatigue resistance, stiffness, hardness, the capacity to withstand dynamic and static stresses, and excellent chemical and mechanical wear resistance. The fracture toughness of zirconia-toughened alumina composites is increased by a factor of four compared to alumina by itself. Zirconia was first included in alumina as a densifier; however, it was not until much later that zirconia was used as a reinforcement particle to increase the level of toughness in the material. The use of ZTA to improve the mechanical properties of orthopedic implants has lately been the subject of several studies, which have all just been concluded. This research includes a literature review primarily concerned with the Biolox Delta composite, its microstructural properties, manufacturing and prosthesis materials for it to identify as a bioceramic material for medical applications.

High temperature tribological performance of molybdenum reinforced zirconia toughened alumina composites prepared by pressure-less sintering

Molybdenum (Mo) reinforced zirconia-toughened alumina (ZTA) composites are a vital class of self-lubricating ceramics with potential applications as seals, dies and cutting tools. However, their tribological behaviours under elevated temperatures remain largely unexplored. The present study investigates the tribological performances of pressure-less sintered ZTA ceramics containing various weight percentages (0, 5, 10 and 15 wt %) of Mo at elevated temperatures (500 °C and 750 °C). Formation of self-lubricating Mo oxides at tribo-interfaces was observed when the temperature increases from 500 °C to 750 °C. The least friction coefficient (0.34) and specific wear rate of (1.057 × 10−4 mm3/N-m) were observed at 750 °C for 15 wt % Mo – ZTA and 10 wt % Mo – ZTA composites respectively. Phase analysis, and morphological and elemental studies on the wear tracks confirmed the presence of molybdenum-oxide-rich thin lubricating tribo-films on the worn surface, and suggest adhesion as the dominant wear mechanism.

Effect of cooling rates on mechanical properties of alumina-toughened zirconia composites

Alumina-toughened zirconia (ATZ) composites are attractive structural ceramics that are widely used in many industrial components owing to their remarkable mechanical properties, such as high strength, hardness, toughness, and wear resistance. These properties are strongly affected by the ZrO2 phase transformation from the tetragonal to the monoclinic phase, which can be induced by external stress. Controlling the microstructure and residual stress generated during the sintering process can control this phase transformation. In this study, to enhance the mechanical properties of ATZ composites, we conducted a systematic investigation on the effect of different cooling rates after sintering ATZ composites with 10 vol% Al2O3 at 1550 °C on the microstructural evolution and residual stress of the matrix phase. The mechanical properties were strongly dependent on the residual stress generated during the cooling process after sintering at elevated temperatures. The ATZ composite with a −1 °C/min cooling rate showed the maximum fracture toughness of 9.5 MPa √ m and the lowest tensile residual stress.

The rising crack resistance curve behavior and mechanism of La2O3 doped zirconia toughened alumina composites prepared via vat photopolymerization based 3D printing

In this study, we combined liquid precursor infiltration of high introduction amounts of bi-additives (20 wt%) and vat photopolymerization-based 3D printing to fabricate zirconia toughened alumina, and the infiltration systems consist of the four following systems Zr4+/La3+, Zr4+/Ce4+, Zr4+/Gd3+, and Zr4+/Er3+. The sample immersed with Zr4+/La3+ shows intense peaks of m-ZrO2 phase compared to the other samples while a new phase of rod-like LaAl11O18 grain occurs in the Zr4+/La3+ immersed sample, the existence of which could be confirmed by XRD and EDS. The fracture toughness of the Zr4+/Ce4+, Zr4+/Gd3+, and Zr4+/Er3+samples remained basically unchanged versus the crack size, with the fracture toughness between 4 MPa m1/2 and 5 MPa m1/2; while the measured fracture toughness values for the Zr4+/La3+ system show a rising crack resistance curve behavior, with the toughness enhanced from 6.37 MPa m1/2 to 8 MPa m1/2. The obvious enhancement of the toughness could be attributed to thermal expansion misfit and rod-like LaAl11O18 in the Zr4+/La3+ system. The toughening mechanism and the effect of residual stresses on the fracture mode are discussed on the basis of theoretical calculation and analysis. The rising crack resistance curve behavior could provide a new toughening strategy in ceramic 3D printing.

Enhanced structural, thermal, mechanical and electrical properties of nano ZTA/epoxy composites

<abstract> <p>Epoxy composites were prepared by doping nano Zirconia Toughened Alumina (ZTA) which were synthesized by solution combustion method into epoxy resin and hardener. Initially ZTA nanopowder was characterized to check its purity, morphology and to confirm its metal-oxide bonding using XRD, SEM and FTIR respectively. The thermal properties such as TGA and DTG were also analysed. The polymer composites were obtained by uniformly dispersing ZTA nanopowder into epoxy using an ultrasonicator. Polymer composites of various concentrations viz, 0.5, 1, 1.5, 2 and 2.5 wt% were synthesized, all concentrations were prepared on weight basis. All the polymer composites were tested for compression properties, flexural properties and tensile properties. Best results for all the mechanical properties were obtained for epoxy with 1.5 wt% ZTA composites. Electrical properties such as breakdown voltage and breakdown strength were analysed and outstanding results were observed for epoxy with 2.5 wt% ZTA composite.</p> </abstract>

The Effect of Sintering Profiles on Zirconia Toughened Alumina (ZTA) Prepared by Two-Stage Sintering

The effects of sintering profiles on the Zirconia Toughened Alumina (ZTA) composite containing 0 vol% Y-TZP (pure alumina) to 20 vol% Y-TZP content prepared by a sintering method known as two-stage sintering were investigated. The heating rate was set between 10°C/min to 20°C/min, T1 set between 1400°C to 1500°C, T2 at 1350°C and holding time was set at 12 hours. The samples’ microstructural properties and mechanical properties, including bulk density, Vickers hardness, Young’s modulus and fracture toughness, were evaluated. Based on the data obtained, the ZTA composites with 10 vol% Y-TZP sintered at a heating rate of 10°C/min and holding time of 12 hours were able to achieve mechanical properties requirements set by the industry standard. In addition, the maximum ZTA composite’s bulk density was recorded to be above 90% T.D, while the Vickers hardness of the composite was recorded to be exceeding 17 GPa. The ZTA composite also recorded maximum Young’s modulus exceeding 380 GPa and fracture toughness above 6 MPam1/2.

Mechanical and Tribological Properties of MgO/Multiwalled Carbon Nanotube-Reinforced Zirconia-Toughened Alumina Composites Developed through Spark Plasma Sintering and Microwave Sintering

Mechanical and Tribological Properties of MgO/Multiwalled Carbon Nanotube-Reinforced Zirconia-Toughened Alumina Composites Developed through Spark Plasma Sintering and Microwave Sintering

Lithography-based manufacturing of advanced ceramics for orthopaedic applications: A comparative tribological study

Ceramics long history in biomedical field is related to their high biocompatibility and mechanical properties. Precisely, for joint replacements, wear resistance is fundamental, so advanced ceramics as alumina and zirconia are preferred. Developments in ceramic additive manufacturing allow for dense ceramic parts with improved mechanical properties and shape accuracy.This paper focuses on the tribological analysis of stereolithography-manufactured components for orthopaedics. Alumina, yttria-stabilised zirconia, 10 and 20 wt% zirconia toughened alumina (ZTA) samples were analysed. The effect of surface finishing, microstructure and microhardness on wear was considered.Printing orientation does not significantly impact microhardness, wettability, and microporosity. However, some printing artefacts as the staircase effect were observed on spherical surfaces. Zirconia system presented high wear rates and friction coefficient, while alumina system showed more acceptable and stable values, with the formation of a self-mated tribofilm. ZTA composites presented the lowest wear volume and better mechanical and surface properties in general.

Densification Behaviour and Mechanical Properties on MgO Doped Zirconia Toughened Alumina (ZTA) Prepared by Two-Stage Sintering

The effect of doping small amounts of Magnesium Oxide ranging between 0 to 1 vol% on Zirconia Toughened Alumina (ZTA) composites which is one of main biomaterial used for production of total hip arthroplasty were investigated. The samples were produced via conventional two-stage sintering with T1 varies between 1450°C and 1550°C with heating rate of 20°C/min. The samples were then rapid cooled to T2 set at 1400°C with holding time of 12 hours. The microstructural and mechanical properties of the two-stage sintered ZTA are then investigated to determine the feasibility of MgO addition. Combination of two-stage sintering at T1 above 1500 and also small amount of MgO up to 0.5 vol% were shown to have positive effect on ZTA which exhibited improvement on its grain size, mechanical properties such as Vickers hardness, Young’s modulus and fracture toughness compared to undoped ZTA composites. The sample with 0.5 vol% MgO addition sintered at T1 of 1500°C and T2 1400°C was able to achieve Vickers hardness of 19.6 GPa, Young’s modulus of 408 GPa and fracture toughness of 6.8 MPam1/2 without significant grain growth compared to undoped ZTA composites.

Environmental footprint as a criterion in the ZTA composites forming process via centrifugal slip casting

The main goal of this study was to optimize the technological process of forming and sintering Zirconia Toughened Alumina (ZTA) composites in terms of reducing energy demand. Based on the results of Life Cycle Assessment carried out according to ISO 14044 and EN 15805 standards, the elimination of preliminary homogenization of ceramic suspension in the planetary mill, allowed to reduce energy consumption by over 25%. The method of forming ZTA materials by CSC method, allowed to obtain finished tube-shaped products, which did not require any mechanical treatment after sintering. Such an approach may be an alternative solution for production of ZTA pipes that can be used in transport of aggressive substances, even in extreme corrosive or temperatures conditions.