Small ZrO2 Research Articles

Evaluation of tensile property and strengthening mechanism of Zirconia reinforced molybdenum alloy

In this experiment, the nano-ZrO2 particles reinforced molybdenum alloy with excellent mechanical properties were prepared through liquid-liquid doping process, and the comparison with TZM alloy prepared by solid-solid doping process was conducted. During the liquid-liquid doping process, the ZrO2 particles ensured the dispersion of the second phase in alloy because they reached molecular-level uniformity, and the hydrothermal synthesis preparation process enabled the ZrO2 particles in alloy to reach nanometer size level. In Mo-ZrO2 alloy, the small and dispersed ZrO2 can effectively block dislocation and passivation cracks; both the room temperature and high temperature performance of Mo-1.5 %ZrO2 alloy was better than that of TZM alloy. Based on the hindered recrystallization process, improved recrystallization temperature, as well as enhanced recrystallization strength thanks to the alloy pinning effect of ZrO2, the maximum tensile stress of Mo-1.5 %ZrO2 alloy at 1000 ℃ was about 14 % higher than pure molybdenum, and the maximum tensile stress of Mo-1.5 %ZrO2 alloy at 1400 ℃ was at least 45 % higher than pure molybdenum. Quantitative analysis shows that the strengthening effect of the second phase was the best during the recrystallization process.

Constructing the highly efficient Ni/ZrO2/SiO2 catalyst by a combustion-impregnation method for low-temperature CO2 methanation

CO2 methanation is conducive to the storage of renewable electricity and the utilization of CO2. Exploiting highly efficient Ni-based catalysts with a simple method is of significance for this reaction. To achieve an excellent low-temperature activity, the attention is focused on the small Ni particles and ZrO2 promoter in this work, which can increase the amounts of H2 and CO2 active sites. Firstly, the simple combustion-impregnation method was employed, forming small Ni particles (about 6 nm). More metal-support interface and increased basicity could be generated in the meantime. Hence, the higher H2 dissociation and CO2 adsorption ability were attained. Secondly, ZrO2 serving as a promoter was beneficial to the formation of oxygen vacancies, which played an important role in CO2 activation and CH4 formation. These oxygen vacancies could weaken the CO bonds, improving the CO2 activation. In addition, they might serve as the H reservoir, increasing the H2 adsorption capacity. Because of the H spillover effect from Ni to ZrO2, the activated H atoms on Ni could react with activated CO2 to generate CH4. Therefore, with more active sites for H2 and CO2 activation, the Ni/ZrO2-COM catalyst exhibited the excellent catalytic performance at 300 °C. This work is of great significance in developing highly efficient Ni-based catalysts at low temperatures for CO2 methanation with a facile method.

Sustainable microwave-assisted hydrothermal synthesis of carbon-supported ZrO2 nanoparticles for H2O2 electrogeneration

This work proposes the use of a novel green and fast (<1h) route for the construction of electrocatalysts by microwave-assisted hydrothermal synthesis using carbon-supported metal oxide for H2O2 electrogeneration. Using ZrO2 supported on carbon black Printex L6 (PL6C) as a non-toxic model catalyst, the present study evaluated different synthesis conditions and their effects on ORR activity and selectivity via the application of the rotating ring-disk electrode (RRDE) and gas diffusion electrode (GDE) techniques. RRDE results showed that the optimized ZrO2/PL6C catalyst presented improvements in catalytic performance of 140 mV in the E1/2 for ORR and in selectivity for H2O2 production of 88.8% compared to the unmodified PL6C (78%). The improved electrocatalytic performance was attributed to the high dispersion of small ZrO2 nanoparticles (~7 nm) in direct contact with the carbon support which helped increase the ECSA values. GDE results showed that ZrO2/PL6C was responsible for doubling the kapp values of H2O2 production and for the reduction of energy consumption by about 150 kWh g−1 compared to the unmodified matrix. Key insights related to the construction of carbon-based metal oxide catalysts and the optimization of ORR are discussed further in the work aiming at providing useful contributions for future investigations and applications.

Biaxial flexural strength, crystalline structure, and grain size of new commercially available zirconia-based ceramics for dental appliances produced using a new slip-casting method

ObjectiveThe aim of this study was to evaluate the biaxial flexural strength, the crystalline structure, and the grain size of zirconia-based ceramics produced using a new slip-casting method. Materials and methodsYttria-stabilized Tetragonal Zirconia Polycrystal (Y-TZP) and Alumina Toughened Zirconia (ATZ) ceramics were purchased from different manufactures. For the experimental group, ceramics produced using a patent pending slip-casting method (Slurry, Decema GmbH) was used. Slurry ceramics (n = 42) with a diameter of 14 ± 0.2 mm were produced by a proprietary colloidal shaping process, sintered, and subsequently polished with a lapping process using 15 μm diamond particles to a thickness of 1.2 ± 0.2 mm. For the control group, ceramics produced using the hot isostatic pressure method (HIP, Metoxit AG) were used. HIP ceramics discs (n = 42) with a diameter of 15.5 ± 0.02 mm were produced by classical HIP method and subsequently machined to a thickness of 1.99 ± 0.04 mm 32 discs of each ceramic were submitted to a biaxial flexural strength test using an universal testing machine at a crosshead speed of 0.5 mm/min. Statistical analyses using two-way ANOVA and Weibull distribution were performed. 2 discs of each ceramic were analyzed using X-ray diffraction for grain crystalline phase quantification. 2 discs of each ceramic were thermally etched and scanning electron microscopy images were obtained for grain size analysis (ISO 13383–1:2012). 6 discs of each ceramic were used for density measurement using the Archimedes’ method. ResultsFor both ATZ and Y-TZP ceramics, the biaxial flexural strength and the characteristic strength of ceramics produced using the Slurry method were significantly higher than ones of the ceramic produced using HIP. The structure analysis confirmed the superiority of the Slurry ceramics which had only 1.2% tetragonal phase compared to 11–16% for the HIP ceramics. Grain size distributions covered a wide range 50–800 nm; the ZrO2 grains of the Slurry ceramics were significantly smaller than the ones of the control ceramics, while the Al2O3 grain distributions were not affected by the manufacturing process. The manufacturing process had no influence on the density of both materials. ConclusionsThe Slurry method using a new proprietary slip-casting method to produce Y-TZP and ATZ dental ceramics presented higher biaxial flexural strength, less monoclinic phase and smaller ZrO2 grains.

One-pot synthesis of uniform hollow nanospheres of Ce–Zr–O mixed oxides by spray pyrolysis

Abstract Ultra-thin hollow nanospheres of Ce–Zr–O mixed oxides were successfully synthesized in a one-pot mode via ultrasonic spray pyrolysis, using a highly diluted aqueous solution of cerium and/or zirconium nitrate salts as nanospheres precursors and glycine as a template. The structure, morphology, and physicochemical properties of the samples were carefully studied by SEM, TEM, XRD, FT-IR, UV–Vis, Raman, and XPS. Obtained nanospheres composed of small CexZryO, CeO2, or ZrO2 nanoparticles with low crystallinity featured high uniformity and relatively low wall thickness (c.a. 5 nm) with an external diameter c.a. 100 nm. It was found that interaction between CeO2 and ZrO2 proceeded almost entirely with the formation of the corresponding mixed phases even at a short residence time (c.a. 2 s) in the high-temperature zone of a spray pyrolysis reactor. To the best of our knowledge, this is the first work on the synthesis of uniform ceria-zirconia hollow nanospheres by spray pyrolysis technique. The suggested approach of Ce–Zr nanospheres synthesis opens an effective, promising, and simple way for large-scale preparation of nanospheres and nanoreactors with a tunable microstructure using different precursors for wide commercial applications.

Optimization of Co-precipitation Condition for Preparing Molybdenum-Based Sulfur-Resistant Methanation Catalysts

In this study, the effects of ZrO2 carrier precursors, MoO3 loading, and washing treatment on the catalytic performance of MoO3/ZrO2 toward sulfur-resistant methanation were investigated. All the catalysts were prepared by co-precipitation method and further characterized by N2 adsorption–desorption, H2-temperature-programmed reduction, X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The prepared MoO3/ZrO2 catalysts were tested in a continuous-flow pressurized fixed bed reactor for CO methanation. The results revealed that the carrier precursors, MoO3 loading, and washing treatment affected not only the crystalline phase of Mo species but also the grain size of ZrO2 carrier and consequently influenced the MoO3/ZrO2 activity toward sulfur-resistant methanation. The 25 wt% MoO3/ZrO2 catalyst prepared using Zr(NO3)4·5H2O as the precursor and treated by water washing displayed the best activity for sulfur-resistant methanation due to its greater number of octahedral Mo species and smaller ZrO2 grain size.

Effect of ZrO2 on Catalyst Structure and Catalytic Sulfur-Resistant Methanation Performance of MoO3/ZrO2–Al2O3 Catalysts

A series of MoO3/ZrO2–Al2O3 catalysts was prepared and investigated in the sulfur-resistant methanation aimed at production of synthetic natural gas. Different methods including impregnation, deposition precipitation, and co-precipitation were used for preparing ZrO2–Al2O3 composite supports. These composite supports and their corresponding Mo-based catalysts were investigated in the sulfur-resistant methanation, and characterized by N2 adsorption–desorption, XRD and H2-TPR. The results indicated that adding ZrO2 promoted MoO3dispersion and decreased the interaction between Mo species and support in the MoO3/ZrO2–Al2O3 catalysts. The co-precipitation method was favorable for obtaining smaller ZrO2 particle size and improving textural properties of support, such as better MoO3 dispersion and increased concentration of Mo6+ species in octahedral coordination to oxygen. It was found that the MoO3/ZrO2–Al2O3 catalyst with ZrO2Al2O3 composite support prepared by co-precipitation method exhibited the best catalytic activity. The ZrO2 content in the ZrO2Al2O3 composite support was further optimized. The MoO3/ZrO2–Al2O3 with 15 wt % ZrO2 loading exhibited the highest sulfur-resistant CO methanation activity, and excess ZrO2 reduced the specific surface area and enhanced the interaction between Mo species and support. The N2 adsorption-desorption results indicated that the presence of ZrO2 in excessive amounts decreased the specific surface area since some amounts of ZrO2 form aggregates on the surface of the support. The XRD and H2-TPR results showed that with the increasing ZrO2 content, ZrO2 particle size increased. These led to the formation of coordinated tetrahedrally Mo6+(T) species and crystalline MoO3, and this development was unfavorable for improving the sulfur-resistant methanation performance of MoO3/ZrO2–Al2O3 catalyst.

Efficient production of biodiesel from both esterification and transesterification over supported SO42−–MoO3–ZrO2–Nd2O3/SiO2 catalysts

SO42−–MoO3–ZrO2–Nd2O3/SiO2 (SMZN/SiO2) catalysts for the production of biodiesel via both esterification and transesterification were prepared and characterized by N2 adsorption-desorption isotherms, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry analysis (TGA), ammonia adsorption Fourier transform infrared spectra (NH3-FTIR), and ammonia adsorption temperature programmed desorption (NH3-TPD) to reveal the dependence of the stable catalytic activity on calcination time. The reason for catalyst deactivation was also studied. The calcination time remarkably affected the types of active centers on SMZN/SiO2, and 4 h was found to be the optimal calcination time. SO42− species bonded with small size ZrO2 were found to be the stable active centers, where the leaching of SO42− and the deposition of coke were inhibited. The deposition of coke was easier on large size ZrO2 than on small size ones. Calcination in air flow could eliminate the deposited coke to recover the deactivated catalysts.

Three different alumina–zirconia composites: Sintering, microstructure and mechanical properties

Two commercial 3mol% yttria–partially stabilized zirconia powders, with 0.3wt% Al2O3 (Y–PSZA) and without Al2O3 (Y–PSZ), and a Zr (IV) precursor were used to produce alumina (Al2O3)–zirconia (ZrO2) slip cast composites. The influence of both the zirconia content and the reduction of zirconia particle size on the sintering behavior, microstructure development and mechanical properties were investigated. The increase in the zirconia content from 10.5 to 22vol% increased the hardness; whereas, above 22vol% ZrO2 the hardness decreased. A significant increase in the fracture toughness with increasing the ZrO2 content over 22vol% was obtained by the stress-induced phase transformation. The flaw size limited the strength below 22vol%; whereas, above 22vol% ZrO2 the strength was controlled by the stress-activated phase transformation. For 10.5vol% ZrO2, the smaller ZrO2 grains produced by using the Zr (IV) precursor were more effective in preventing the Al2O3 grain growth resulting in higher hardness. However, the tetragonal–monoclinic (t–m) transformation of some unstabilized ZrO2 grains during cooling reduced Young's modulus and fracture toughness.

Size-dependent density of zirconia nanoparticles.

The correlation between density and specific surface area of ZrO2 nanoparticles (NPs) was studied. The NPs were produced using a hydrothermal process involving microwave heating. The material was annealed at 1100 °C which resulted in an increase in the average grain size of the ZrO2 NPs from 11 to 78 nm and a decrease in the specific surface area from 97 to 15 m2/g. At the same time, the density increased from 5.22 g/m3 to 5.87 g/m3. This effect was interpreted to be the result of the presence of a hydroxide monolayer on the NP surface. A smaller ZrO2 grain size was correlated with a larger contribution of the low density surface layer to the average density. To prove the existence of such a layer, the material was synthesized using 50% heavy water. Fourier transform infrared spectroscopy (FTIR) permitted the identification of the –OD groups created during synthesis. It was found that the –OD groups persisted on the ZrO2 surface even after annealing at 1100 °C. This hydroxide layer is responsible for the decrease in the average density of the NPs as their size decreases. This study of the correlation between particle size and density may be used to assess the quality of the NPs. In most cases, the technological aim is to avoid an amorphous layer and to obtain fully crystalline nanoparticles with the highest density possible. However, due to the effect of the surface layers, there is a maximum density which can be achieved for a given average NP diameter. The effect of the surface layer on the NP density becomes particularly evident for NPs smaller than 50 nm, and thus, the density of nanoparticles is size dependent.

Sintering and Microstrusture of Al2O3 and Al2O3-ZrO2 Ceramics

Alumina powder and two commercial 3 mol% yttria-partially stabilized zirconia powders–0.3 wt% Al2O3-doped (Al-Y-PSZ) and without Al2O3 (Y-PSZ)–were used to produce alumina-zirconia (Al2O3-ZrO2) slip cast composites. The influence of the substitution of Al2O3 by 50 vol% of the different zirconia powders on the sintering kinetic at the intermediate stage was investigated. In addition, the microstructure of Al2O3 and the different composites at temperatures in the range of 1100-1600°C was studied and related to the sample hardness. An increase in the sintering rate was observed when 50 vol% Y-PSZ was substituted by 50 vol% Al-Y-PSZ. 50 vol% zirconia was effective to reduce the rate of Al2O3 grain growth in the final sintering stage. For 50 vol% Al-Y-PSZ a smaller ZrO2 grain size distribution compared with 50 vol% Y-PSZ could be achieved. As the average Al2O3 grain size of the sintered samples became greater than about 1μm a markedly decrease in the hardness was found; this occurred at temperatures higher than 1400°C, since de composites with 50 vol% zirconia reduced the rate of Al2O3 grain growth a decrease in hardness up to 1600°C was not observed.

Enhanced electro-magnetic properties in La0.7Sr0.3MnO3/ZrO2 composites

(La0.7Sr0.3MnO3)1−x /(ZrO2) x (x = 0.0–0.150, step 0.025) composites have been prepared via solid state reaction process. The X-ray diffraction and scanning electron microscopic observations indicate that there are ZrO2 grains separated from La0.7Sr0.3MnO3 matrix. It has been found that the inclusion of ZrO2 content decreases the conductivity, magnetization and metal–semiconductor transition, whereas it increases the low field magnetoresistance. Possible effects of grain boundaries on the low field magnetoresistance have been discussed. The small ZrO2 grains are trapped between La0.7Sr0.3MnO3 grains may be acting as a barrier for spin-polarized tunneling and enhance the low-field magnetoresistance.

Ultrafine Polishing of Electroless Nickel–Phosphorus-Plated Mold with Magnetic Compound Fluid Slurry

Electroless nickel–phosphorus (Ni–P)-plated mold for hot press of optical lens must be manufactured to nanolevel surface roughness. The single-crystal diamond turning (SCDT) process is generally used to machine the Ni–P plating layer to attain the required form and ultrafine surface finish. However, this process frequently causes concentrically arranged tool marks to appear on the work surface. In this study, the Ni–P plating layer was polished with magnetic compound fluid (MCF) slurry to remove the tool marks. Two MCF slurries were used, one containing high-quality carbonyl iron particles (CIPs) and alumina (Al2O3) abrasive particles (1 µm), and the other containing CIPs coated with zirconia (ZrO2) abrasive particles (50–100 nm). First, spot polishing without relative motion between the center of the MCF carrier and the workpiece was carried out using both slurries. Then, scanning polishing with the MCF carrier moving along a motion path was carried out using only the MCF slurry containing ZrO2-coated CIPs. Although both slurries removed the SCDT-induced tool marks on the work surface, the MCF slurry containing relatively large Al2O3 abrasive particles left scratches and frequently caused CIPs to be embedded in the Ni–P plating surface, which inversely worsened the work surface roughness. In contrast, the MCF slurry containing relatively small ZrO2 abrasive particles resulted in an improved work surface roughness, without scratches or the embedding of particles. The cross-sectional profile of the polishing spot manifests a characteristic symmetrical W-shape. The dot-shaped scratches were induced at the spot center, and the lengths of these scratches increase with the increase in the distance from the spot center. In scanning polishing, the W-shaped polishing spot moves along the designed scanning path and instantaneous overlapping occurs, which significantly improves the flatness of the Ni–P plating layer from 0.2 to 0.1 µm. In addition, almost all the particles can move relative to the work surface, and the surface finish of the Ni–P plating layer was improved, without scratches or the embedding of particles. The preliminary results show that the MCF polishing is applicable to the nanolevel finishing of soft magnetic materials.

Pore Structure Model of Bimodal Catalyst Supports

Co/ZrO2–SiO2 bimodal catalyst has higher activity and higher selectivity for the Fischer-Tropsch synthesis than conventional catalysts. This study investigated the catalyst support pore structure in detail, especially the formation of small pores with a model analysis. The analysis considered 10 wt% ZrO2–SiO2 and 20 wt% ZrO2–SiO2 bimodal catalyst supports with various loadings of ZrO2. Higher loadings of ZrO2 from 10 to 20 wt% decreased the large pore size from 59.8 to 56.7 nm, resulting in the promotion of the formation of small ZrO2 pores inside the large SiO2 pores. Interestingly, small pore size remained unchanged at 3.9 nm, irrespective of the ZrO2 loading, indicating that the small pore size was determined by the character of the ZrO2 nanoparticles participating in the self-assembly of ZrO2 nanoparticles inside the large SiO2 pores. A theoretical model of the agglutination of ZrO2 nanoparticles was established, and used to analyze the formation of small ZrO2 pores. The model suggested that 12 ZrO2 nanoparticles formed a unit cell with diamond lattice structure. The obtained small pore size and large pore size were very close to the experimental findings, and the calculated specific surface area and pore volume were also similar to the measured values.

ZrO2 influence on structure and properties of some alkali lime zinc aluminosilicate glass ceramics

Glass–ceramics raw glazes in the Na2O–K2O–CaO–Al2O3–ZnO–SiO2 system with low ZrO2 additions (0, 3 and 5wt%), used as nucleating agent, were synthesised and thermally treated at 1250°C. Willemite (Zn2SiO4), sanidine (K0.831 Na0.169Al Si3O8), gahnite (ZnAl2O4) and zircon (Zr2SiO4) were the main crystalline phases identified by X-ray investigations in the resulting glazes. An increase of the ZrO2 content from 0 to 5wt% trigged an increase of the crystallinity degree from 71.34% to 83.73% and gahnite crystallite size from 176 to 336Å. Further, morphological and structural data of these glass–ceramics were supplementary determined by SEM, MAS-NMR of 27Al and 29Si and Raman Spectroscopy. The structural modifications in terms of the glass ceramic compositions, especially small ZrO2 additions to the expense of the SiO2 and the relationship between composition and colour characteristics of the glazes are investigated and presented in this paper.

Processing of different alumina–zirconia composites by slip casting

Two Al2O3–ZrO2 mixture preparation routes: classical powder mixing and addition of a Zr (IV) precursor solution to a well dispersed Al2O3 suspension, were used to produce alumina (Al2O3)–zirconia (ZrO2) slip cast composites. For the conventional powder mixing route, two commercial 3 mol% yttria-partially stabilized zirconia powders, 0.3 wt% Al2O3-doped (Al-doped Y-PSZ) and without Al2O3 (Y-PSZ), were employed. The influence of the zirconia content and the solid loading on the rheological properties of concentrated aqueous Al2O3–ZrO2 slips were investigated. The density of green samples was studied and related to the degree of slip dispersion. In addition, the influence of the processing conditions on the density and microstructure development of sintered samples were investigated. By using the Zr (IV) precursor route, nano-sized ZrO2 (ZN) particles homogeneously distributed on the Al2O3 particle surfaces were obtained; however, it let to aggregates of some Al2O3 particles with very fine ZrO2 uniformly distributed. The viscosity and yield stress values of Al2O3–ZN suspensions were markedly higher than those of Al2O3–Al-doped Y-PSZ and Al2O3–Y-PSZ ones, for all the compositions and solid loading studied and resulted in a less dense packing of cast samples. However, for the composite with 10.5 vol% ZN a high sintered density and a smaller ZrO2 grain size distribution compared with the conventional powder mixing route could be obtained.

Synthesis and Characterization of Nanocomposites with Strong Interfacial Interaction: Sulfated ZrO2 Nanoparticles Supported on Multiwalled Carbon Nanotubes

We discuss the synthesis of a composite of ZrO2 nanoparticles supported on multiwalled carbon nanotubes (MWCNT). Using X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM), the ZrO2 were found to be 2–3 nm tetragonal crystalline nanoparticles. Strong interfacial interaction between the ZrO2 nanoparticles and the MWCNT surface was observed by near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the carbon K-edge and the oxygen K-edge, and this strong metal oxide/support interaction leads to small ZrO2 particle size and thermal stability. The ZrO2/MWCNT was converted into a solid acid catalyst by sulfation, and the properties of S-ZrO2/MWCNT were studied. The nature of the acid sites was probed by S K-edge and Zr L-edges (L3, L2, L1) XANES as well as catalytic probe reaction of cyclohexane dehydrogenation/cracking. Such composites would be good candidates for potential catalysis applications in fuel cell electrodes and biomass processing.

High Performance BaTiO3‐Based BME‐MLCC Nanopowder Prepared by Aqueous Chemical Coating Method

Dispersion plays an important role in aqueous chemical coating process for the preparation of BaTiO3‐based powder for base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) in our previous research. In this article, a powerful sand mill (SC‐milling) machine is utilized instead of traditional ball milling to produce BaTiO3 MLCC nanopowder, in which small ZrO2 beads help to achieve high centrifugal accelerations and avoid BaTiO3 agglomerates. As much as 1 kg BaTiO3 nanopowder has been effectively dispersed very well in one time, then a uniform coating of additives on BT nanoparticles has been achieved by aqueous chemical coating method. High performance X7R BaTiO3 nanoceramics with the average grain size of about 96 nm are obtained. The experimental result indicates that this technology can be feasible to the industry for manufacturing next generation BME‐MLCCs.

Superficial severe plastic deformation of 316 LVM stainless steel through grit blasting: Effects on its microstructure and subsurface mechanical properties

The microstructure and mechanical properties of austenitic stainless steel 316 LVM (Low Vacuum Melting) blasted with either small and rounded ZrO2 particles or larger and angular shaped Al2O3 particles are analysed through magnetic force microscopy, synchrotron radiation diffraction and ultramicroindentation techniques. It is shown that blasting causes a severe plastic deformation that roughens the surface and produces a significant subsurface grain refinement and work hardening. The gradient in the plastic deformation and the volume increase associated with the deformation induced α′-martensite account for the development of compressive residual stresses with a maximum value close to the surface. All these features yield a gradient in hardness with a maximum value beneath the surface. Compared with the Al2O3 particles, the ZrO2 particles cause a higher value of compressive residual stress and a lower increase in hardness. Also, the Al2O3 particles lead to more α′-martensite formation at deeper regions from the surface than the ZrO2 particles. The different results are related with the specific morphology of the particles and their specific role in the blasting process.

Microstructure and mechanical properties of a directionally solidified Al2O3/Y3Al5O12/ZrO2 hypoeutectic in situ composite

Directionally solidified ternary Al2O3/Y3Al5O12(YAG)/ZrO2 hypoeutectic rod composites were successfully fabricated by the laser zone remelting technique. The microstructure and mechanical properties of the composite were investigated. The microstructure presented a complex three-dimensional network structure consisting of fine Al2O3 (41vol.%) and YAG (49vol.%) phases, with smaller ZrO2 (10vol.%) phases partially distributed at the Al2O3/YAG interfaces. The irregular growth behavior in the hypoeutectic was revealed. The hardness and fracture toughness at ambient temperature were measured to be 17.3GPa and 5.2MPam1/2, respectively. The toughness enhancement in comparison with previous binary Al2O3/YAG composites was mainly attributed to the refined microstructure, and crack deflection, branching and bridging. Moreover, the residual stresses, generated by different thermal expansion coefficients of the component phases, also importantly contributed to the improved toughness. Correlations between the addition of the third component ZrO2 and the microstructure and properties were discussed as well.