Zirconia Toughened Alumina Research Articles

In-situ synthesis and characterization of calcium phosphate coatings on rapidly solidified zirconia toughened alumina eutectic bioceramics by laser cladding

Rapidly solidified zirconia toughened alumina (ZTA) eutectic bioceramics are promising load-bearing materials that meet the needs for durability and aging resistance for biomedical applications. However, one of the major problems is their poor bioactivity which may lead to aseptic loosening after long-term service. To solve this problem, calcium phosphate (Ca-P) coatings are in-situ synthesized on rapidly solidified ZTA eutectic bioceramics by laser cladding technology with mixed powders of CaHPO4∙ 2H2O and CaCO3 after granulation as precursors. X-ray diffraction results show that Ca-P coatings are mainly composed of Ca0.2Zr0.8O1.8, AlPO4, Ca4P2O9, Ca3(PO4)2 and Ca2P2O7. The amount of calcium phosphates reaches a maximum when using a laser power of 800 W and a scanning rate of 650 mm/min. Cross-sectional morphologies and energy dispersive spectrometer analysis indicate excellent interfacial bonding between the substrate and coating. In vitro tests prove that Ca-P cladded samples can induce apatite with flake-like morphology similar to those on the bioceramic coatings cladded on titatinum alloy precipitation and promote MC3T3-E1 cell proliferation. This work reveals that laser cladding has the potential to improve the biomineralization of solidified ZTA eutectic bioceramics enabling prolonged clinical service life.

Reinforcing potential of MWCNTs on mechanical and machining performance of hot-pressed ZTA-MgO ceramic cutting inserts

A new generation cutting insert was manufactured by multi-walled carbon nanotube (MWCNT) reinforcement (0–0.25 weight percentage (wt%)) into zirconia toughened alumina (ZTA)- magnesium oxide (MgO) ceramic matrix using a powder metallurgy route. The hot-press sintering technique was used to compact the uniformly mixed ZTA-MgO-MWCNT powders, sintered at 1500 °C followed by morphological, mechanical and functional characterizations. The relative densities of the samples were between 98 % and 99 %. The mechanical properties of the matrix were improved up to 0.15 wt% MWCNTs. The highest microhardness was ~2366 HV0.5 for 0.15 wt% due to grain refinement by synergistic pinning between spinel (MgAl2O4) and MWCNTs. Similarly, the highest indentation fracture toughness was ~7.33 MPa.m1/2 for 0.15 wt% MWCNT content due to micromechanical interlocking mechanism from a combined effect of MWCNT size variation and inter-particle distance between MWCNTs featuring proper crack bridging and crack deflection. To function as a cutting insert, the sintered samples up to 0.15 wt% was selected and shaped according to SNGN120408 cutting tool geometry. For minimum cutting force with high surface roughness, the optimized parameters were observed as a cutting speed of 300 m/min, feed rate of 0.12 mm/rev and 0.2 mm depth of cut using the design of experiment technique while machining AISI 4340 steels. Furthermore, regression models were developed to correlate the machinability with machining conditions. The comparative study suggested that the significant improvement of cutting force (~26.4 %), surface roughness (~55.3 %) and tool life (~29.4 %) was achieved for ZTA-MgO-0.15 wt% MWCNT ceramic tool with respect to ZTA-MgO inserts depending upon self-lubrication phenomenon alongside with the retention of proper tool geometry for a longer tool life ~44 min. The morphological and Raman spectra analysis of the worn region justifies the self-lubricating phenomenon at the interface by breaking and rolling of MWCNTs.

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.

The gross slip fretting corrosion mechanisms of biomedical ceramic-metal couples

Fretting corrosion in taper joints is of concern since the mid-1970s. Thus, different metallic and ceramic material combinations have been tested and used clinically. While the stem is typically made of Ti-alloy the head materials can vary and may consist of CoCrMo-base alloys, alumina- or zirconia-based ceramics, and materials that rely on surface engineering. Based on retrieval analysis as to the acting mechanisms in real taper joints we tested some of these material combinations under gross slip fretting corrosion as one of the failure mechanisms at ultra-mild wear rates. We found that the main submechanisms for the generation of the tribomaterial (or 3rd-body) – which remains in contact and provides boundary lubrication – are microploughing, microcutting, and mechanical mixing, while the wear loss is brought about by the ejection of metal ions (and wear particles) and predominantly governed by the balance between tribocorrosion and triboxidation. We also showed that topography plays a major role under these circumstances. On the basis of ultra-mild wear gross-slip fretting corrosion experiments we demonstrated that non-self-mating combinations of Ti6Al4V against CoCr29Mo6 or zirconia-toughened alumina (ZTA) ceramic show a smaller wear loss provided that the reaction products can act as boundary lubricants. In addition, the material properties of bodies, counterbodies and the interfacial medium are also governed by the topographies in contact and their capability to act as reservoir for the tribomaterial. Hence, the fluted Ti6Al4V worked best against polished ZTA under these specific test conditions.

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.

Effect of microwave sintering on the properties of copper oxide doped alumina toughened zirconia (ATZ)

This study investigated the effect of copper oxide addition on the alumina toughened zirconia composite ceramic using microwave sintering. CuO amounts (0.05–1 wt%) were examined at sintering temperatures (1250–1500 °C). Investigations covered hardness, toughness, phase stability, microstructure, and densification. Optimum doping was 0.2 wt%, resulting in a composite with 99% relative density at 1500 °C, Vickers hardness of 13.1 GPa, and fracture toughness of 7.1 MPa m1/2. Low-temperature degradation showed disrupted phase stability above 1400 °C, with CuO unable to prevent ageing-induced phase transformation.

Effect of manganese addition on sintering behavior and mechanical properties of alumina toughened zirconia

The effect of MnO2 additives on the sintering behavior and mechanical properties of alumina-toughened zirconia (ATZ, with 10 vol% alumina) composites was investigated by incorporating different amounts of MnO2 (0, 0.5, 1.0, and 1.5 wt%) and sintering at various temperatures ranging from 1300 to 1450 °C. The addition of MnO2 up to 1.0 wt% improved the sintered density, hardness, flexural strength, and fracture toughness of the composite. However, the addition of 1.5 wt% MnO2 degraded the relative density, hardness, and flexural strength of the composite due to the transformation of the ZrO2 phase from tetragonal to monoclinic and grain coarsening. Optimal results were obtained with 1.0 wt% MnO2 and sintering at 1450 °C, which improved the mechanical properties (hardness: 13.5 GPa, flexural strength: 1.2 GPa, fracture toughness: 8.5 MPa m1/2) and lowered the sintering temperature compared to the conventional sintering temperature of ATZ composites (1550 °C). Thus, the ATZ composite doped with MnO2 is a promising material for structural engineering ceramics owing to its improved mechanical properties and lower sintering temperature.

Wear behaviour of alumina-toughened-zirconia composites with different phase arrangement under ball-on-flat tribological tests

ABSTRACT 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 room temperature and 400°C. Tetragonal zirconia balls were used as a counterpart. Two different types of microstructure were designed, one consisting of separated alumina inclusions in a zirconia matrix 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 both materials showed a distinct decrease in the wear rate. Composite with a low alumina content showed minimal wear rate at 300°C and composite with higher amount of alumina showed it at 400°C. There are some observations that this minimal wear rate result is connected with a pseudoplastic behaviour of a layer formed between co-operating elements of tribological pair. This layer is composed of the debris of both, sample and counterpart, and its behaviour during sliding is connected with the mean grain size of this debris which is correlated with the mean grain size of sintered material.

Hybrid microwave sintering of Zirconia Toughened Alumina in a multimode cavity – Influence of the content of 3 mol% yttria stabilized zirconia and sintering configurations

MW sintering is a sintering process in which samples directly heat by absorption of the electromagnetic field, leading to a fast volume heating. Thus, the materials are heated due to their own dielectric properties. Zirconia Toughened Alumina (ZTA) is of particular interest for MW sintering because of the difference of dielectric properties between alumina and zirconia. In this study, ZTA pellets with different volume fractions of zirconia were sintered in a MW multimode cavity with different sintering cells, i.e., with or without susceptor. These experiments show that all the samples were densified whatever the configuration. But the evolution of power and temperature vs time during the sintering cycle shows a better heating capability when the volume fraction of zirconia increases. The influence of the material to heat is more visible when sintering without susceptor. This was confirmed by other experiments, where the samples were heated by a constant incident power in a single-mode cavity.

Study on wettability behavior and wear resistance mechanism of ZTA-ceramic-reinforced HCCI composites

ABSTRACT Zirconia-toughened alumina (ZTA)-reinforced high-chromium cast iron (HCCI) composite materials were prepared using pressureless sintering method, and the effects of the type (titanium (Ti), nickel (Ni)) and content (10%, 12%) of active additives on the wettability and wear resistance were systematically studied. Result showed that the additive can enhance the wettability capacity between ZTA/HCCI composites interface, especially Ti, which reacted the chemical reaction and formed a transition layer in metallurgical combination. When the content of the Ti additive was 10%, the Brinell hardness (HB) of ZTA/HCCI composite was 573.1 N/mm2 at room temperature, and the wear-resistant properties were more than 3.8 times of pure HCCI. After thermal treatment, the HB and wear resistance of 10% Ti-ZTA/HCCI composites increased significantly which could reach 629.8 N/mm2 and were more than 4.3 times of the pure HCCI, respectively.

Interface characteristics and wear resistance of Ni-B4C plated ZTA reinforced high chromium cast iron composite

A chemical composite plating of Ni-B4C was used to prepare the surface-modified zirconia toughened alumina (ZTA) ceramic particles. The ceramic preforms were prepared by the plated ZTA and sodium silicate solution binder, followed by casting infiltration to prepare the ZTA particles reinforced high chromium cast iron (HCCI) composites. The result reveals that a distinct interface layer forms at the ZTA/HCCI interface, which consists of phases of ZrB2, FeB, Fe2B, and NaSiO4. The interfacial wettability between ZTA and HCCI is improved by the diffusion and reaction of Ni and B4C. The wear test reveals that the Ni-B4C plated ZTA particles can effectively improve the wear resistance of the ZTA/HCCI composite, and the wear rate of the composite is decreased to 11.6% of HCCI.

Mechanical properties and wear behaviors of Cu-doped zirconia-toughened alumina ceramics

Cu-doped, ZrO2-toughened alumina (ZTA) ceramics with varying amounts of Cu (0, 1.5, 3.0, and 5.0 wt%), denoted as Cu/ZTA, were prepared using a fast hot pressing sintering furnace. The microstructure, mechanical properties, tribological properties, and wear mechanism of Cu/ZTA ceramics were subsequently studied. The results showed that Cu doping can cause the formation of holes in the ZTA ceramics. The formation of holes originated from the O2 produced by CuO decomposition at high temperatures and the phase transformation of ZrO2. Cu/ZTA ceramics with 5.0 wt% Cu exhibited significantly improved toughness and tribological properties but diminished hardness. The worn surface analysis of the Cu/ZTA ceramics revealed that their wear mechanism primarily involved abrasive wear and material transfer. The ZrO2 and Cu particles were first pulled out from the wear track to form wear debris during friction. The 5.0 wt% Cu/ZTA ceramic exhibited decreased hardness and high toughness, which made it easier for the abrasive debris to adhere to the surface and holes. Additionally, the wear debris was crushed into the holes formed by Cu doping. The results indicated that a reduction in the number of wear particles at the friction interface could impede the wear of the abrasive particles. Overall, the Cu/ZTA ceramic with 5.0 wt% Cu was found to be a promising structure material with excellent tribological properties.

Fretting corrosion behavior of Ti6Al4V alloy against zirconia-toughened alumina ceramic in simulated body fluid

The fretting corrosion at the head-neck interface of artificial hip joints is an important reason for the failure of prostheses. The Ti6Al4V alloy-zirconia-toughened alumina (ZTA) ceramic combination has been widely used to make the head and neck of artificial hip joints. In this study, its fretting corrosion behavior in simulated body fluid was studied by electrochemical monitoring, surface morphology characterization, and chemical composition analysis. A running condition fretting map (RCFM) of load and displacement was established, including three regimes, namely partial slip regime (PSR), mixed fretting regime (MFR), and gross slip regime (GSR). The friction dissipation energy increased gradually from the PSR to MFR and GSR. In the PSR, the damage mechanisms were slight abrasive wear and tribocorrosion at the edge of contact area, as well as extremely slight adhesive wear at the center. In the MFR, the damage mechanisms were mainly adhesive wear, abrasive wear, and corrosive wear. In the GSR, the damage mechanism was serious abrasive wear, fatigue wear, and corrosive wear combined with slight adhesive wear. Finally, an ion-concentration map was created, displaying the material-loss transition of different displacements and loads. The material loss increased with the increased displacement, and increased first and then decreased with the increased load.

Cutting performance and wear mechanism of zirconia toughened alumina ceramic cutting tools formed by vat photopolymerization-based 3D printing

Zirconia toughened alumina (ZTA) cutting tools are widely used for machining hard and wear-resistant materials. However, the processing of ZTA ceramic cutting tools with complex shapes using traditional methods is difficult and time-consuming. Until now, to the best of our knowledge, commercial ceramic cutting tools do not contain grooves because it is very difficult to process grooves on the ceramic cutting tool, resulting from the feature of high hardness and brittle attribute of ceramics. This study investigated high-performance, complex-shaped zirconia-toughened alumina (ZTA) ceramic cutting tools equipped with a chip breaker for the first time. The investigated samples were prepared using vat photopolymerization based 3D printing combined with a hot isostatic sintering process. The relative density of 99.34%, Vickers hardness of 17.98 ± 0.20 GPa, bending strength of 779 ± 47 MPa and fracture toughness of 5.41 ± 0.29 MPa m1/2 of the ZTA cutting tools were obtained. The effects of three cutting parameters, namely the cutting speed vc, feed rate f, and back cutting depth ap, on the cutting performances of the cutting tools were investigated, and the wear mechanisms of the cutting tools were examined. We believe that our study makes a significant contribution to the literature because this study provides an in-depth investigation of the properties and wear mechanisms of ZTA ceramic cutting tools with chip breaker grooves. The findings of this study provide insight into the preparation of high-performance, complex-shaped ZTA ceramic cutting tools. Further, the preparation methods investigated in this study and the evaluation of the properties of the fabricated specimens in comparison with a commercially available cutting tool illustrate the potential advantages that may be obtained via the further development of these materials.

Evaluation of Fracture Toughness of Plasma Electrolytic Oxidized Al2O3-ZrO2 Coatings Utilizing Nano-Scratch Technique

Al2O3 coatings, which can be produced by plasma electrolytic oxidation (PEO) on aluminum substrates, provide an excellent protection against corrosion and wear. However, due to the brittle nature of the oxide ceramic, the fracture toughness is limited. One approach to enhance the tolerance to fracture is the incorporation of ZrO2 to form zirconia toughened alumina (ZTA). In addition to its use as a bulk material, the application as a coating material enables a broader field of application. In this study, an Al2O3-ZrO2 composite coating was applied on a 6082 aluminum alloy using an aluminate-phosphate-based electrolytic solution containing a Zr-based salt. Polarization measurement as an indicator of the passivability of a given system revealed that Zr-based salt improves the passivation of the aluminum alloy. The coatings’ characteristics were evaluated by SEM, EDS, and XRD. ZrO2 incorporated into alumina as a metastable high-temperature modification led to a thicker coating with new morphologies including lamellar and dendritic structures. Nano-indentation showed that the incorporated Zr increase the average hardness of the compact layer from 16 GPa to 18 GPa. The fracture toughness of the coatings was investigated locally with nano-scratches applied on the compact outer layer of the coatings’ cross-sections. The Zr-containing electrolytic solution resulted in a coating with significantly higher fracture toughness (6.9 MPa∙m1/2) in comparison with the Zr-free electrolytic solution (4.6 MPa∙m1/2). Therefore, it is shown, that the PEO process stabilized a high-temperature allotrope of zirconia at room temperature without the need for rare-earth dopants such as Y2O3. Furthermore, it was demonstrated that the nano-scratch method is a suitable and accurate technique for the investigation of the fracture toughness of coatings with inherent cracks.

Formulation for zirconia toughened alumina (ZTA) reinforced metal matrix composites based on a three-phase concentric inclusion model

In this paper, a model of a coated inhomogeneous circular inclusion concentrically embedded within a finite matrix is proposed, which is employed to analyze zirconia toughened alumina (ZTA) reinforced metal matrix composites. The general solution is derived based on the equivalent eigenstrain principle and the superposition principle. Then, the model is used to study the influence of the thermal strains due to temperature changes on the stress distribution in the composite. Also, a particular composite, ZTA reinforced high chromium cast iron (HCCI), is exemplified, and the normalized stress distribution is given. In addition, the toughening mechanism associated with the transformation of zirconia is discussed. The above results help to estimate the stress level of ZTA reinforced metal composites. This three-phase concentric inclusion model is expected to be used to the structure design of composite materials.

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.

Fabrication and characterization of alumina and zirconia-toughened alumina porous structures

In the present study, alumina (Al2O3) and zirconia-toughened alumina (ZTA) porous structures (foams) were manufactured using the space holder technique. Al2O3 and ZTA foams with varying porosities from 20% to 69% were fabricated by adding different sizes (10, 20, and 40 μm) and different volume % of polystyrene beads (space holders) to Al2O3 and ZTA powders. All the fabricated foams were investigated under static conditions to assess the compressive behavior. It is observed that the compressive strength of these foams strongly depends on porosity, pore size, pore size distribution and pore wall thickness. Among all fabricated foams, Al2O3 foams with 20 vol% beads of 10 μm size showed a higher compressive strength of 700 MPa with low porosity (21%) and a higher pore wall thickness (2.8 μm). It is also observed that the pore wall thickness decreased with the increase in beads size and the volume % of the beads, resulting in a low compressive strength value of 8 MPa with a lower pore wall thickness of 1.75 μm at 80 vol% of 40 μm beads. All the foams, irrespective of pore size, showed a typical ceramic failure phenomenon up to 70 vol% of beads; after that, the failure behavior changed to complete open-cell fracture.

Material extrusion-based additive manufacturing of zirconia toughened alumina: Machinability, mechanical properties and biocompatibility

Material extrusion-based additive manufacturing (MEAM) has gained significant attention due to its versatile flexibility for fabricating a broad range of materials. In this study, fabrication of dense zirconia-toughened alumina (ZTA) ceramics with micro/nano powders of excellent mechanical and biological properties was investigated. The ZTA paste rheology was engineered to achieve appropriate rheological behavior. A novel machining scheme on MEAM produced ZTA green parts using CNC milling and high precision micro-milling was studied to investigate their effect on surface integrity and geometric accuracy. The MEAM produced ZTA ceramics show the highest relative density, Vickers hardness, bending strength, and fracture toughness of 99 %, 17.7 GPa, 422.5 MPa, and 6.2 MPa*m1/2, respectively. Biocompatibility of fabricated ZTA ceramics with different size of powders was investigated including cell adhesion, cell toxicity and cell proliferation, showing a good potential in biomedical usage. This framework provides a unique pathway for MEAM of ZTA ceramics to combine design and manufacturing freedom, multifunctionality, stability, and economical simultaneously.

Zirconia-Toughened Alumina Ceramic Wear Particles Do Not Elicit Inflammatory Responses in Human Macrophages.

Ten percent of patients undergoing total hip arthroplasty (THA) require revision surgery. One of the reasons for THA are wear particles released from the implants that can activate the immune defense and cause osteolysis and failure of the joint implant. The discrepancies between reports on toxicity and immunogenicity of the implant materials led us to this study in which we compared toxicity and immunogenicity of well-defined nanoparticles from Al2O3, zirconia-toughened alumina (ZTA), and cobalt chrome (CoCr), a human THP-1 macrophage cell line, human PBMCs, and therefrom-derived primary macrophages. None of the tested materials decreased the viability of THP-1 macrophages nor human primary macrophages at the 24 h time point, indicating that at concentrations from 0.05 to 50 µm3/cell the tested materials are non-toxic. Forty-eight hours of treatment of THP-1 macrophages with 5 µm3/cell of CoCr and Al2O3 caused 8.3-fold and 4.6-fold increases in TNF-α excretion, respectively, which was not observed for ZTA. The comparison between THP-1 macrophages and human primary macrophages revealed that THP-1 macrophages show higher activation of cytokine expression in the presence of CoCr and Al2O3 particles than primary macrophages. Our results indicate that ZTA is a non-toxic implant material with no immunogenic effects in vitro.