Yttria Stabilized Zirconia Content Research Articles

Exploration into the microstructural, mechanical, and biological characteristics of the functionally graded 3Y-TZP/Ti6Al4V system as a potential material for dental implants

This study investigated the mechanical, microstructural, and biological properties of 3Y-TZP/Ti6Al4V functionally graded material (FGM) fabricated by the spark plasma sintering (SPS) method. For this purpose, 11 layers of 100-x vol% Ti6Al4V/x vol% Yttria stabilized zirconia (YSZ) (x = 0 to 100) were sintered at 1450 °C and a pressure of 30 MPa for 8 min. To investigate the properties of each layer in more detail, 11 batches of 100-x vol% (Ti6Al4V)/x vol% YSZ (x = 0 to 100) composites were sintered separately with the same sintering conditions mentioned for the FGM sample. Phase identification of the FGM sample showed the formation of Ti3O, c-ZrO2, and Zr3O phases as by-products. A schematic model was proposed for the formation of the mentioned phases with the aid of thermodynamic calculations. The formation of these phases was confirmed by microstructural and elemental tests. The results of the relative density of the samples showed that these values were obtained for each layer above 99%. The microhardness of 590 ± 18 Vickers was obtained for Ti6Al4V; by increasing the amount of 3Y-TZP, this value reached 1510 ± 24 Vickers for the YSZ sample. The fracture toughness value for Ti6Al4V was 39.2 ± 2 MPa m0.5, which was significantly reduced to 4.84 ± 1 MPa m0.5 by adding 10 vol% YSZ. After that, with the further increase of YSZ, this value increased slowly. A similar trend was observed for the bending strength of the samples. By increasing 3Y-TZP from 0 to 30 vol%, the bending strength was decreased from 1556 ± 32 to 272 ± 62 MPa. By further increasing the amount of 3Y-TZP from 30 to 100 vol%, an increase in the bending strength was observed in the samples, which reached 1180 ± 71 MPa for the YSZ sample. The FGM sample showed a brittle fracture despite a metal layer, but a higher bending strength (982 ± 44 MPa) was obtained for this structure than the composite samples. The biological results show that increasing YSZ content leads to a decrease in antimicrobial activity. Additionally, all samples demonstrated high biocompatibility based on MTT cytotoxicity tests after 1 and 7 days of culture.

Decomposition behavior of yttria-stabilized zirconia and its effect on directed energy deposited Ti-based composite material

• The present study focuses on the rule of YSZ nanoparticles in the refined both α and β grains and increased strength of additively manufactured Ti-6Al-4 V (Ti64). • The YSZ nanoparticles decomposed during the deposition process and led to the formation of Y 2 O 3 and some excess oxygen in the Ti64 matrix. • The decrease in the sizes of the prior β grains could be attributed to the increasing amount of dissolved oxygen and yttrium, which promoted constitutional supercooling. • The reduction in the size of the α grains could be ascribed to a shift of the onset of the β → α+β transformation to a higher temperature and shorter time with increasing concentration of dissolved oxygen. • The contributions of the underlying strengthening mechanisms (α grain size, oxygen solid solution, Y 2 O 3 precipitate) for the as-deposited specimens were quantitatively determined. We report on the microstructure and the strengthening mechanisms of additively manufactured parts fabricated by directed energy deposition of Ti-6Al-4V (Ti64) powders blended with yttria-stabilized zirconia (YSZ) nanoparticles. These specimens showed refined microstructures as compared to bare as-deposited Ti64, where the α and columnar prior β grain sizes decreased with increasing YSZ content. The YSZ nanoparticles decomposed during the deposition process and led to the formation of yttrium oxide and some excess oxygen in the Ti64 matrix. The decrease in the sizes of the prior β grains could be attributed to the increasing amount of dissolved oxygen and yttrium, which promoted constitutional supercooling. Furthermore, the reduction in the size of the α grains could be ascribed to a shift of the onset of the β → α+β transformation to a higher temperature and shorter time with increasing concentration of dissolved oxygen. Finally, the contributions of the underlying strengthening mechanisms for the as-deposited specimens were quantitatively determined.

Mechanical and microstructural properties of yttria-stabilized zirconia reinforced Cr3C2-25NiCr thermal spray coatings on steel alloy

In this research work, nano yttria-stabilized zirconia (YSZ) reinforced Cr3C2-25NiCr compo­site coatings were prepared and successfully deposited on ASME-SA213-T-22 (T22) boiler tube steel substrates using high-velocity oxy-fuel (HVOF) thermal spraying method. Different nanocomposite coatings were developed by reinforcing Cr3C2-25NiCr with 5 and 10 wt.% YSZ nanoparticles. The nanocomposite coatings were analysed by scanning elec­tron microscope (SEM)/Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) technique. The porosity of YSZ- Cr3C2-25NiCr nanocomposite coatings was found to be decreasing with the increase in YSZ content, and hardness has been found to be increasing with an increase in the percentage of YSZ in the composite coatings. The coating of 10 wt.% YSZ-Cr3C2-25NiCr showed the lowest porosity, lowest surface roughness, and highest microhardness among all types of coatings. This may be due to the flow of YSZ nanoparticles into the pores and gaps that exist in the base coatings, thus providing a better shield to the substrate material.

Influence of yttria-stabilized zirconia content on rheological behavior and mechanical properties of zirconia-toughened alumina fabricated by paste-based stereolithography

Improvement of the mechanical properties of advanced ceramics fabricated by additive manufacturing has been a prerequisite for their wide applications. In this work, zirconia-toughened alumina (ZTA) parts with a variety of yttria-stabilized zirconia (YSZ) content were fabricated by stereolithography (SL) technology, based on the appropriate self-holding ability of the viscoelastic paste and application of conformal contactless support strategy. Combining microstructural analysis and mechanical assessment by three-point bending and indentation tests, the influence of YSZ content on the SL process and subsequent mechanical properties was discussed. The results showed that the optimized matching of flexural strength (477.54 MPa) and fracture toughness (6.56 MPa m1/2) was acquired by ZTA ceramic with a YSZ content of 20 wt%. When the YSZ content reached 30 wt%, agglomerations formed and led to a negative influence on the properties of ZTA ceramics. It is confirmed that the combined contribution from the addition of YSZ on the improvement of mechanical property and influence of the SL process should be synthetically considered during the design of ceramic paste feedstock for such additive manufacturing.

Microstructure and tribological properties of laser cladded TiAlSi composite coatings reinforced by yttria-stabilized zirconia

The YSZ (yttria-stabilized zirconia)/TiAlSi composite coatings were successfully fabricated on Ti–6Al–4V alloy substrates by laser cladding technology. The effects of YSZ content on the microstructure and properties of the laser cladding TiAlSi composite coatings were investigated by optical microscope, scanning electron microscope, x-ray diffractometer, hardness tester, as well as friction and wear testing apparatus. The results show that YSZ reinforced Ti-based composite coatings are mainly composed of TiAl, Ti3Al, Ti5Si3, Al2O3, TiO2, SiO2 and ZrO2. With the increase of YSZ content from 0%–5%, the microhardness of the coatings increases, which reaches a maximum of around 803 HV0.3 when the addition content is 5%. The average coefficient of friction of the coating without YSZ is 0.592, while that of the coatings with 1%, 3% and 5% YSZ contents is 0.433, 0.581 and 0.429, respectively. The composite coating with 5% content of YSZ particles possesses the lowest coefficient of friction. The average wear volume loss of the coating without YSZ is 0.78 mm3, which is higher than that of the coatings with the addition of YSZ. The composite coating with 5% content of YSZ particles possesses the lowest wear volume loss. Its worn surface is smoother than the other coatings.

Formation and oxidation resistance of a new YSZ modified silicide coating on Mo-based alloy

A new YSZ (yttria stabilized zirconia) modified silicide coating was prepared on Mo-based alloy through a two-step process, including spraying of Si-Mo-YSZ slurry followed by reaction sintering. Microstructure and oxidation behavior of the coatings with different YSZ content (0, 5, 10 and 15%) were studied. The coating consists of a MoSi2-ZrSi2-SiO2 outer layer and a MoSi2 inner layer. The 10% YSZ modified coating possessed the best oxidation protection at ultra-high temperatures and, for the coating, the mass gain was 0.96 mg/cm2 after being exposed at 1725 °C in air for 22 h, whereas the uncoated Mo-based alloy completely ablated for 0.35 h. The excellent oxidation resistance of the silicide coating was attributed to the compact and self-healing SiO2 protective scale, which contained the dispersed ZrO2 and ZrSiO4.

Microstructural characterization and dry sliding wear behavior of spark plasma sintered Cu-YSZ composites

In the present study, yttria stabilized zirconia (YSZ) reinforced Cu matrix composite specimens were produced by spark plasma sintering (SPS). For comparison, pure Cu specimen was also produced in the same conditions. The effect of particles content on microstructure, relative density, electrical conductivity, and Vickers hardness was evaluated. The pin-on-disk test was also performed to determine dry sliding wear behavior of specimens under different wear conditions. After sliding wear tests, the worn surfaces were examined by field emission scanning electron microscopy (FE-SEM). Microstructural study showed satisfactory distribution of reinforcement particles in copper matrix. The relative density up to 95% was obtained for all specimens. By increasing YSZ content from 0 to 5% (volume fraction), the electrical conductivity of specimens decreased from 99.2%IACS to 65%IACS, correspondingly. The hardness of Cu-5%YSZ composite specimen was two times greater than that of pure copper. The volume loss and wear rate of pure Cu specimen were 1.48 mm3 and 1.5×10−3 mm3/m under 50 N applied load and 1000 m sliding distance. However, for composite containing 5% YSZ particles, these values dropped to 0.97 mm3 and 0.9×10−3 mm3/m, respectively. Moreover, the friction coefficient of specimens was changed from 0.6 to 0.4. The worn surface and debris observation indicate local plastic deformation and delamination as dominant wear mechanisms for pure copper, while oxidation and ploughing for composite specimen. Accordingly, it can be concluded that the Cu-YSZ composite could be a good candidate for the electrical contact applications in relays, contactors, switches and circuit breakers requiring good electrical and thermal conductivity and capability to resist wearing.

Strength evaluation of glass–ceramic composites containing yttria stabilized zirconia after thermal cycling

The effect of YSZ (yttria stabilized zirconia) on the thermal cycling stability of commercial glass–ceramics powders as a solid oxide fuel cell (SOFC) sealant material is investigated. Four different composite sealants are prepared including 1, 3, 5 and 10wt% of YSZ with respect to the total powders. A sealant without YSZ is also prepared as the base case for comparison. The fabrication of the sealant is achieved by using cost-effective tape casting routes. The samples are then placed between two metallic interconnectors and a high temperature glass forming process is performed. The mechanical performances are measured via tensile tests before and after a number of thermal cycles. The results indicate that the fracture strength is adversely affected by the amount of YSZ loading due to reduced glass–ceramics powders in the composites. However, when the thermal cycling stability is the issue, the samples with YSZ show relatively small rate of decrease. Therefore, the addition of YSZ is found to be beneficial for improving the thermal cycle stability of glass–ceramics. The optimum YSZ content is determined to be 5wt%, since these samples exhibit almost a stable mechanical performance after each thermal cycles considered in this study.

Effects of YSZ Additions on Thermoelectric Properties of Nb-Doped Strontium Titanate

The effect of yttria-stabilized zirconia (YSZ) with a low thermal conductivity on the thermoelectric properties of Nb-doped SrTiO 3 bulk materials, which were fabricated by the conventional normal pressure sintering method in an Ar atmosphere, was examined. YSZ additions reduced the thermal conductivity but significantly enhanced the electrical conductivity. However, the Seebeck coefficient was nearly independent of YSZ content. Thus, the ZT value was enhanced, and a sample with 3 wt.% YSZ displayed the maximum ZT value, 0.21, at 900 K. Additionally, the reason for the reduced thermal conductivity and enhanced electrical conductivity by YSZ additions was investigated in detail.

Oxygen Reduction Kinetics at Dense ( La0.85Sr0.15 ) 0.9MnO3 – YSZ Composite Electrodes Investigated Using Potentiostatic Current Transient Method

The oxygen reduction kinetics was investigated at dense (LSM)–yttria-stabilized zirconia (YSZ) composite electrodes as a function of YSZ content of by using the potentiostatic current transient (PCT) technique combined with ac-impedance spectroscopy. From the discrete Fourier transformation analysis of impedance spectra, the individual reaction steps were successfully differentiated and the distribution of relaxation time for ion migration was quantitatively estimated for oxygen ion migration as well. The cathodic PCTs were characterized by decay and buildup transients, which corresponded to the oxygen reduction current at the three-phase boundaries (TPBs) and the current at the LSM surface superimposed on the steady-state current at the TPBs , respectively. As the YSZ content increased, the equilibrium exchange flux at the LSM surface decreased and the difference between the steady-state currents at the TPBs and at the LSM surface increased in absolute value. These results strongly indicate that when the YSZ content increases, the contribution of the facile ion migration to is suppressed by the prevailing contribution of the sluggish charge transfer reaction at the LSM surface and oxygen reduction at the TPBs predominantly contributes to the overall oxygen reduction than that reduction at the extended active sites.

In situ tribometry of solid lubricant nanocomposite coatings

The friction and wear behavior of nanocomposite coatings comprised of yttria stabilized zirconia (YSZ), Au, carbon and MoS 2 were studied by in situ tribometry in both dry nitrogen (3–5% RH) and humid air (35–45% RH). Transfer film formation and interfacial dynamics were evaluated by direct observation of the sliding contact through a sapphire hemisphere. Four different third-body velocity accommodation modes (VAMs) were identified: (1) interfacial sliding, (2) interfacial sliding combined with transfer film shearing, (3) plowing and (4) local plowing and transfer film extrusion. The first two VAMs were associated with low, stable friction in dry and humid environments. The second two VAMs were associated with high friction in dry conditions and increased wear. Tribological performance and VAMs were also correlated with coating composition and mechanical properties. Friction spiking occurred for coatings with greater YSZ content. Harder coatings exhibited high friction run-in that was more pronounced for coatings with high carbon content. In situ experiments demonstrated that friction and wear performance was controlled by stable transfer film formation and VAMs associated with a lubricating condition (interfacial sliding or transfer film shearing).

Electrochemical and structural characterisation of zirconia reinforced hydroxyapatite bioceramic sol–gel coatings on surgical grade 316L SS for biomedical applications

Yttria-stabilized zirconia (YSZ)/hydroxyapatite (HAP) composite coatings on surgical grade 316L stainless steel was carried out using sol–gel dip coating and calcination process. Various molar ratios of HAP and YSZ was developed, each YSZ/HAP gel coating showed an average particle size of ∼30 nm and the coatings were dried and calcined for crystallization. The functional group and crystallization characteristics of the coatings were analyzed using (FT-IR), X-ray diffraction (XRD) and energy dispersion X-ray analysis (EDXA). The formation of β-tricalcium phosphate (β-TCP) was controlled changing the Ca/P ratio in HAP phase and also YSZ content in the composite coatings. It was revealed that TCP content showed a very minimum value at Ca/P ratio of ∼1.67 and at YSZ content of 30 vol.%, respectively. The mechanism of increased β-TCP content with Ca/P ratio lower than 1.67 and increased YSZ content was explained as Ca-deficiency due to the Ca-diffusion into t-ZrO 2 crystals to form a solid solution. The resultant coatings were analysed for its corrosion resistance through polarisation, impedance and ICP-AES analysis in simulated body fluid. The viability of the reinforced coatings were analysed by in vitro cell culture studies.

Processing-Microstructure-Property Relations in Anisotropic Thermal Sprayed Composites

AbstractThermal spray is a significantly advanced but inherently complex deposition process that involves successive impingement of molten droplets on a substrate to form coating with a ¡°brick-wall¡± layered structure. The anisotropic microstructure of coatings is very sensitive to processing conditions and has significant influence on the properties. This study aims to understand the processing-microstructure-thermal property correlation of thermally sprayed coatings. Thermal transport properties of three coating systems forming composites with pores (yttria stabilized zirconia (YSZ) -Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) are interpreted from the point of view of microstructure and chemical composition. In the case of YSZ-Air composite, results indicate that porosity contribution from 20-35% decreases the thermal conductivity by 50-70% of the bulk value. For the intrinsic composite of Mo and Mo2C, which coexist as stable phases, thermal conductivity increases significantly with 1.75wt% carbon addition since it reduces formation of MoO2 during processing, but decreases with 3.5wt% carbon addition. This is attributed to larger carbide retention in the latter. For the discrete layered and graded composites of YSZ-NiCrAlY, which are made up of varying fractions of these two constituents, thermal conductivity decreases sharply up to 40wt% YSZ and then more gradually with increasing YSZ content. This paper examines these experimental findings by treating the these complex coatings as multiphase composites.

Bioconductivity and mechanical properties of plasma-sprayed dicalcium silicate/zirconia composite coating

Dicalcium silicate (C 2S)/yttria stabilized zirconia (YSZ) composite coatings possessing better durability and more superior mechanical properties than pure C 2S coatings were produced by atmospheric plasma spraying. The microstructure and phase composition of the composite coatings were determined by scanning electron microscopy and X-ray diffraction. The bioconductivity of the coatings was evaluated in vitro by incubating in simulated body fluids (SBF). Apatite was observed to precipitate even on coatings comprising more than 70% YSZ after immersion in SBF for 7 days. The changes of the mechanical properties of the composite coatings due to immersion in SBF were also investigated. The durability was found to increase with a larger YSZ content in the coatings. Deterioration of the mechanical properties can be attributed to the degraded interlamellar or cohesive bonding due to fast dissolution of C 2S. This study reveals factors affecting the durability of the C 2S/YSZ composite coatings in simulated physiological environment and suggests means for improvement to address clinical needs.

Crystallization characteristics of yttria-stabilized zirconia/hydroxyapatite composite nanopowder

Yttria-stabilized zirconia (YSZ)/hydroxyapatite (HAp) composite nanopowder was synthesized using a chemical precipitation and calcination process. Each YSZ/HAp gel powder showed an averaged particle size of ∼50–100 nm and it was dried and calcined for crystallization. The crystallization characteristics of each powder were analyzed using X-ray diffraction (XRD) and quantitative analyses were performed on each phase using quantitative XRD (Q-XRD). The formation of β-tricalcium phosphate (β-TCP) was controlled changing the Ca/P ratio in HAp phase and also YSZ content in the composite nanopowder. It was revealed that β-TCP content showed a minimum value at Ca/P ratio of ∼1.73 and at YSZ content of 10 wt%, respectively. The mechanism of increased β-TCP content with Ca/P ratio lower than 1.73 and increased β-TCP content with YSZ content was explained as Ca-deficiency due to the Ca-diffusion into t-ZrO2 crystals to form a solid solution, which was confirmed analyzing the lattice parameter change of t-ZrO2 crystals. The composite nanopowder with Ca/P ratio of 1.77 showed formation of CaO crystals, resulting in the increase in β-TCP content.

A novel combustor based on chemical-looping reactions and its reaction kinetics.

A novel combustor based on controlled chemical-looping reactions without flame differs from the traditional combustor, in which the fuel is in direct contact with air. It allows CO2 to be easily recovered and promises advanced-level thermal efficiency for power generation. Promising results of laboratory experiments with the novel combustor are presented here. We found that NiO particles mixed with YSZ (yttria-stabilized zirconia) have very good properties with respect to oxidation rate, conversion, and physical strength. Especially, the rate of oxidation of Ni particles is increased significantly. The effects of YSZ content in the particle, the reaction temperature, the particle size, and the water vapor concentration were examined by studying the kinetic behavior of reactions. These promising results revealed high potential for applying chemical-looping combustion in a power-generation plant.