Al2O3-ZrO2 Composites Research Articles

Effect of machining environments on the crack behavior of ZrO2-Al2O3 composite during short-pulsed laser processing

The ZrO2-Al2O3 exhibits distinct behavior compared to monolithic ceramics when exposed to stress. The compelling quality of this trait makes it well-suited for any demanding supporting application that necessitates resilience. However, under a thermal process, it might cause functional concerns such as cracking patterns, which pose a threat to the endurance of orthopedic implants. This issue has lately attracted medical scrutiny. Being a thermal process, fiber laser treatment of ZrO2-Al2O3 is more complex than monolithic ceramic because of its unique thermal characteristics and varied rates of absorption, which rely on the matrix and the reinforcement material. This research aims to scrutinize the divergent characteristics of ZrO2-Al2O3 in terms of crack behavior while treating it with the same laser fluence under auxiliary environments. It has been found that ZrO2-Al2O3 prone to form cracks when processed under high-temperature environments due to the development of stress during phase transformation because of prolonged exposure, as evidenced by the surface characterization results. Meanwhile, when it was processed at low-temperature environments like water and ice, the detrimental effect of laser fluence factor appeared to be meager by reducing the likelihood of phase transformation and crack quantity. With this, the research demonstrates a promising approach that effectively maintains the overall structural integrity of ZrO2-Al2O3 by impeding the progression of the cracks along with a smooth, flawless surface during laser processing.

The volume erosion rate of the slip cast monolithic and composite ceramics

ABSTRACT The volume erosion rate of the slip cast monolithic and composite ceramics was studied using SiO2 and SiC particles as erodents, under different impact angles (30°, 60°, 90°), at room temperature. Therefore, three groups of samples were prepared: (i) monolithic alumina (Al2O3); (ii) composite alumina–zirconia (Al2O3–ZrO2) containing 99 wt-% Al2O3 and 1 wt-% ZrO2 and (iii) composite alumina–zirconia (Al2O3–ZrO2) containing 90 wt-% Al2O3 and 10 wt-% ZrO2. Erosion mechanisms of all prepared ceramic samples were evaluated by the volume erosion rate (, mm3·g–1). Obtained results were compared with the analytical Wiederhorn and Evans equations. The mechanical properties (hardness and fracture toughness) of prepared ceramic samples were compared with their under the above-mentioned conditions. It was found that the erosion of monolithic and composite ceramics increased with the increase of the impact angle. Volume erosion rate was highest at an impact angle of 90° and amounts to 115 mm3·g–1 with SiC, and 12 mm3·g–1 with SiO2 erodent particles for monolithic alumina ceramics, 77 mm3·g–1 with SiC, and 8 mm3·g–1 with SiO2 erodent particles for ceramics with the addition of 1 wt-% of ZrO2, and 61 mm3·g–1 with SiC, and 7 mm3·g–1 with SiO2 erodent particles for ceramics with the addition of 10 wt-% of ZrO2. Therefore, it can be concluded that the erosion resistance of monolithic Al2O3 increases with the increasing amount of ZrO2 in the composite Al2O3-ZrO2 ceramics, thus erosion resistance can be improved with the addition of ZrO2.

Comprehensive analysis of the microstructure, properties and environmental performance of Al2O3-ZrO2 composites obtained via centrifugal slip casting

This research investigates the possibility of preparing Al2O3-ZrO2 composites with different proportions of the Al2O3 and ZrO2 phases by centrifugal slip casting (CSC) method and the effect of the solid phase content (50 vol%, 45 vol%, 40 vol%) on the microstructure and selected properties of the produced materials. The hardness results showed that all the series produced were characterised by high hardness, in the range of 16–19 GPa. The results of the static compression test demonstrated that increasing the solid phase content of the slip in the samples promotes the formation of fewer cracks during the monotonic compression loading of the composites. The LCA results demonstrated that as the content of ZrO2 in the composites increase, their environmental footprint increases.

Flash sintering of Al2O3–ZrO2 ceramics under alternating current electric field

In this study, the influence of alternating current (AC) electric field on flash sintering and microstructural evolution of alumina–zirconia (Al2O3–ZrO2) composite was systematically investigated at furnace temperature of 800 °C. Compared with direct current (DC) electric field, AC electric field not only promoted densification and grain growth of Al2O3–ZrO2 composite, but also improved the uniformity of microstructure of ceramics. Grain size of AC flash-sintered samples was found to be inversely related to electric field, and positive correlation was observed with current density limit. Dense Al2O3–ZrO2 composite ceramic was fabricated via AC flash sintering under 60 mA mm−2 at low furnace temperature within 120 s, and as-sintered samples exhibited relatively good mechanical properties. The mechanism involving synergistic effect of Joule heating and defects generation under the influence of electric field was proposed to explain rapid densification during AC flash sintering. These results indicate the feasibility of preparation of dense composite ceramic with homogeneous microstructure via AC flash sintering.

Fabrication of Al2O3-ZrO2 composite catalysts with tunable acid-base properties for highly efficient aldol condensation of furfural with acetone

A series of alumina-zirconia composite catalysts were fabricated via a homogeneous two-step solution-phase strategy and employed in the aldol condensation of furfural with acetone to produce furfurylidene acetone (FAc). It was demonstrated that after tuning the surface acid-base properties of Al2O3-ZrO2 composites by varying the Al content, a superior catalytic performance (Al/(Al + Zr) ratio of 0.5) with a FAc yield of larger than 90.0% compared to single metal oxides and other mixed metal oxides reported was obtained.

The Potential of Al2O3\u2013ZrO2-Based Composites, Formed via CSC Method, in Linear Infrastructure Applications Based on Their Mechanical, Thermal and Environmental performance

Ceramic-ceramic composites have been prepared using the centrifugal slip casting method (CSC). The method has so far been mainly utilized in making ceramic-metal composites. Al2O3–ZrO2 composites have been obtained with different shares of ZrO2, i.e., 15, 50 and 75 vol pct, respectively. Prior to sintering the composite samples, the rheological properties of the casting slips were investigated and thermogravimetric tests were performed. Upon sintering, all three series of the ceramic composites showed a density close to 100 pct and no microcracks or delamination. Phase, microstructural and mechanical investigations were carried out to determine what effect the share of ceramics has on the composites produced. An increase in the share of ZrO2 in the Al2O3–ZrO2 composite leads to a reduction in the growth of Al2O3 grains and a decrease in the average hardness. Cross-sectional hardness testing of the composites showed no evident gradient in any of the samples. Life cycle analysis (LCA) results indicate that the further optimization of the composite formation process, including up-scaling, allows to obtain Al2O3–ZrO2-based pipes possessing more favorable environmental characteristics compared with materials conventionally used for linear infrastructure, which is important in light of the global transformation toward sustainable construction and the circular economy.Graphical abstract

Effects of Al2O3–ZrO2 content on the densification, microstructure, and mechanical properties of cemented tungsten carbides

In order to prepare cobalt-free cemented carbide by liquid phase sintering, various contents of Al2O3–ZrO2 by eutectic ratio were utilized as binders for tungsten carbides. The effects of Al2O3–ZrO2 content on the densification, microstructure, mechanical properties, and interfacial characteristics of these binderless tungsten carbides were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), high–resolution transmission electron microscopy, and mechanical properties tests. The fully dense WC toughened by Al2O3–ZrO2 composite powders could be consolidated through spark plasma sintering at 1600 °C. The results indicated that a small amount of eutectic Al2O3–ZrO2 binder phase (up to 3 wt%) would aggregate, increasing the contact chance of WC particles and eventually leading to abnormal growth of WC grains. When the Al2O3–ZrO2 content increases to 6.0 wt%, the abnormal growth of WC particles was inhibited by the pinning effect of the well-distributed second phase. The mean grain size of WC decreased with the increasing amount of Al2O3–ZrO2 content, while the mean grain size of Al2O3–ZrO2 colony increased. The temperature corresponding to the maximum shrinkage rate of densification process decreased with increasing Al2O3–ZrO2 content. In general, with the increase of the eutectic ceramic content, the hardness of the composite decreased and the indentation fracture toughness increased. The toughening mechanisms include crack deflection, crack bridging and t– to m–ZrO2 phase transformation toughening. The WC–Al2O3–ZrO2 composites show maximum toughness of approximately 10.5 MPa m1/2 and hardness value of 22.29 GPa, respectively.

Effect of ZrO2 content on the microstructure and flexural strength of Al2O3–ZrO2 composites with the stored failure energy-fragmentation relations

High flexural strength is an important mechanical property for a ceramic armor component to withstand high tensile stresses and protect its structural integrity against multiple hits. Also, larger fragments are required in fragmentation as larger fractured parts are harder to leave of the way for the penetrator and cause more abrasion and higher penetration resistance. In this study, the effect of different ZrO2 content (0, 0.5, 1, 3, 5, 10, 20 vol%) on the flexural strength of Al2O3–ZrO2 composites was investigated with relationship of the stored failure energy-crack length to evaluate the fragmentation behavior under possible impact conditions. Monotonic equibiaxial flexural strength test was used to measure the fracture strength. The highest strength was obtained for 20 vol% ZrO2 containing composite as 435 ± 78 MPa, ~ 24% increase in comparison with the pure Al2O3. The transformation of tetragonal to monoclinic phase occurred during the strength test in the 10 and 20 vol% ZrO2 content composites. 20 vol% ZrO2 containing composite had the smallest total crack length accompanying the largest fragment size for a given fracture energy among all the composites due to the stress-induced transformation of ZrO2 consumes energy that results in decreasing effective crack driving energy required for the crack branching.

Clariant's MegaMax 800 catalyst demonstrates outstanding performance at CNOOC'S Davy methanol plant in Hainan, China

High flexural strength is an important mechanical property for a ceramic armor component to withstand high tensile stresses and protect its structural integrity against multiple hits. Also, larger fragments are required in fragmentation as larger fractured parts are harder to leave of the way for the penetrator and cause more abrasion and higher penetration resistance. In this study, the effect of different ZrO2 content (0, 0.5, 1, 3, 5, 10, 20 vol%) on the flexural strength of Al2O3–ZrO2 composites was investigated with relationship of the stored failure energy-crack length to evaluate the fragmentation behavior under possible impact conditions. Monotonic equibiaxial flexural strength test was used to measure the fracture strength. The highest strength was obtained for 20 vol% ZrO2 containing composite as 435 ± 78 MPa, ~ 24% increase in comparison with the pure Al2O3. The transformation of tetragonal to monoclinic phase occurred during the strength test in the 10 and 20 vol% ZrO2 content composites. 20 vol% ZrO2 containing composite had the smallest total crack length accompanying the largest fragment size for a given fracture energy among all the composites due to the stress-induced transformation of ZrO2 consumes energy that results in decreasing effective crack driving energy required for the crack branching.

The Effect of ZrO2 as Different Components of Ni-Based Catalysts for CO2 Reforming of Methane and Combined Steam and CO2 Reforming of Methane on Catalytic Performance with Coke Formation

The role of ZrO2 as different components in Ni-based catalysts for CO2 reforming of methane (CRM) has been investigated. The 10 wt.% Ni supported catalysts were prepared with ZrO2 as a support using a co-impregnation method. As a promoter (1 wt.% ZrO2) and a coactive component (10 wt.% ZrO2), the catalysts with ZrO2 were synthesized using a co-impregnation method. To evaluate the effect of the interaction, the Ni catalyst with ZrO2 as a coactive component was prepared by a sequential impregnation method. The results revealed that the activity, the selectivity, and the anti-coking ability of the catalyst depend upon the ZrO2 content, the Ni-ZrO2 interaction, basicity, and oxygen mobility of each catalyst resulting in different Ni dispersion and oxygen transfer pathway from ZrO2 to Ni. According to the characterization and catalytic activation results, the Ni catalyst with low ZrO2 content (as a promoter) presented highest selectivity toward CO owning to the high number of weak and moderate basic sites that enhance the CO2 activation-dissociation. The lowest activity (CH4 conversion ≈ 40% and CO2 conversion ≈ 39%) with the relatively high quantity of total coke formation (the weight loss of the spent catalyst in TGA curve ≈ 22%) of the Ni catalyst with ZrO2 as a support is ascribed to the lowest Ni dispersion due to the poor Ni-ZrO2 interaction and less oxygen transfer from ZrO2 to the deposited carbon on the Ni surface. The effect of a poor Ni-ZrO2 interaction on the catalytic activity was deducted by decreasing ZrO2 content to 10 wt.% (as a coactive component) and 1 wt.% (as a promoter). Although Ni catalysts with 1 wt.% and 10 wt.% ZrO2 provided similar oxygen mobility, the lack of oxygen transfer to coke during CRM process on the Ni surface was still indicated by the growth of carbon filament when the catalyst was prepared by co-impregnation method. When the catalyst was prepared by a sequential impregnation, the intimate interaction of Ni and ZrO2 for oxygen transfer was successfully developed through a ZrO2-Al2O3 composite. The interaction in this catalyst enhanced the catalytic activity (CH4 conversion ≈ 54% and CO2 conversion ≈ 50%) and the oxygen transport for carbon oxidation (the weight loss of the spent catalyst in TGA curve ≈ 7%) for CRM process. The Ni supported catalysts with ZrO2 as a promoter prepared by co-impregnation and with ZrO2 as a coactive component prepared by a sequential impregnation were tested in combined steam and CO2 reforming of methane (CSCRM). The results revealed that the ZrO2 promoter provided a greater carbon resistance (coke = 1.213 mmol·g−1) with the subtraction of CH4 and CO2 activities (CH4 conversion ≈ 28% and CO2 conversion ≈ %) due to the loss of active sites to the H2O activation-dissociation. Thus, the H2O activation-dissociation was promoted more efficiently on the basic sites than on the vacancy sites in CSCRM.

Phenolic compounds removal from aqueous solution by composite of alumina-zirconia

ABSTRACT Recently, composite of metal oxide has continually elicited tremendous attention from research scientist globally as a viable adsorbent for the removal of phenol and its derivative from aqueous media owing to their improved physicochemical structures which enhanced adsorption capacity. In this study, a composite of alumina-zirconia (Al2O3–ZrO2) was synthesised by calcination techniques and characterised using scanning electron microscopy–energy dispersive X-ray Spectroscopy (SEM-EDX), and X-ray diffraction (XRD). Results from characterisation revealed the formation of this composite with amorphous structure. The composite was employed to evaluate the performance removal of phenol and 2,4-dichlorophenol from solutions using the batch adsorption technique by considering the influence of varying solution pH, initial concentration, adsorbent dosage, contact time and temperature. The optimal conditions predicted from the study are pH of 7 and 8 at a contact time of 90 minutes for phenol and 120 minutes for 2,4-dichlorophenol, respectively, at a temperature of 301 K. The isothermic empirical models of Langmuir, Freundlich and and Dubinin-Radushkevich were employed. The Freundlich model best described the adsorption process with R 2 correlation values (0.945–0.998). The pseudo-second-order kinetics model adequately depicted the rate of adsorption with higher correlation values (≥0.99) for both compounds as compared to the pseudo-first order. The thermodynamic parameters computed suggest non-spontaneous, exothermic reaction and decreased randomness. The study portends the composite Al2O3–ZrO2 composite to be viable for removal of phenolic compounds from wastewater.

Irradiation response of Al2O3-ZrO2 ceramic composite under He ion irradiation

The dense Al2O3-ZrO2 ceramic composite prepared by spark plasma sintering was irradiated by 500 keV He ions with different fluences and temperatures. The microstructural evolution and mechanical properties were investigated. The results showed that peak broadening and shifts at RT revealed by GIXRD and Raman are associated with damage induced microstrain and formation of point defects. The recovery at 500 °C suggested the reduction of irradiation induced damage. Compared with α-Al2O3, t-ZrO2 exhibited a reverse trend in lattice parameters change and lattice expansion. Many helium bubbles with oblate and ribbon-like shape were mainly formed in α-Al2O3 grains at He concentration peak at 1.0 × 1017 ions/cm2. With increasing of fluence at RT, ribbon-like helium bubbles developed into microcracks at 4.0 × 1017 ions/cm2. Though evident structural changes, no full amorphization was observed at 4.0 × 1017 ions/cm2. Formation of ribbon-like bubbles and microcracks is the main mechanism for degradation of mechanical properties of irradiated Al2O3-ZrO2 composite.

Directed laser deposition of Al2O3–ZrO2 melt-grown composite ceramics with multiple composition ratios

Melt-grown Al2O3–ZrO2 hypoeutectic, eutectic and hypereutectic ceramics were fabricated using directed laser deposition (DLD) technology. Flexural strength of DLD-fabricated Al2O3–ZrO2 composites was obtained for the first time. Toughening mechanisms of ZrO2 in different composition ratios were revealed. The results show that hypoeutectic ceramics form composite microstructure with α-Al2O3 primary dendrites discretely distributing in eutectic continuous matrix, while the discrete phase becomes t-ZrO2 in hypereutectic ceramics. Eutectic ceramic has lamellar fine eutectic colony structure. Hypoeutectic ceramics show the best hardness, while eutectic ceramics have the highest flexural strength of 237 MPa. Fracture toughness reaches the maximum of 5.91 MPa m1/2 under hypereutectic composition, which is 16.8% higher than that of eutectic ratio. Primary t-ZrO2 dendrites in hypereutectic ceramics have phase transformation toughening effect. However, as a eutectic structure phase, t-ZrO2 in hypoeutectic and eutectic ceramics has no phase transformation toughening effect because its size is smaller than the critical size of phase transformation.

Enhanced mechanical properties of ZrO2-Al2O3 dental ceramic composites by altering Al2O3 form

ObjectivesThis study evaluates the difference in physical and mechanical properties of ZrO2 ceramics, commonly used in dental applications, altered by three different forms of Al2O3 content; microparticles (m), nanoparticles (n), and microfiber (f). MethodsThree different types of ZrO2–Al2O3 composites were formed using microparticle (m), nanoparticle (n), or microfibre (f) forms of Al2O3. The physical and mechanical properties such as sintering shrinkage, relative density, Vickers hardness, fracture toughness, and biaxial strength were evaluated. A Weibull analysis was performed to assess the strength reliability of the specimens. All data were calculated using the t-test and ANOVA. ResultsThe sintering shrinkage and relative density of all ceramic composite groups were decreased with the addition of Al2O3. The mechanical properties of ZrO2–Al2O3 (f) composite were higher than that of ZrO2–Al2O3 (m) composite and ZrO2–Al2O3 (n) composite. The maximum hardness, fracture toughness, and biaxial flexural strength were observed for 10 vol% of Al2O3 fibre. When the content of Al2O3 fibre in the matrix was increased above 20 vol%, agglomeration occurred and resulted in a decrease of hardness and toughness. The Weibull modulus value of the ZrO2–Al2O3 (f) composite was the lowest compared to that of other groups. However, characteristic strength (σ0) of ZrO2–Al2O3 (f) the highest value. SignificanceThe current study demonstrated that the addition of right amount of Al2O3 microfibre into the ZrO2 matrix enhanced the mechanical properties of ZrO2-Al2O3 (f) composite, which would be favourable for dental applications.

Sintering and Properties of ZrO2–Al2O3 Composites with Additives Forming Melts Based on Sodium Silicate

A wide range of compositions of zirconia-based composites containing 0, 5, 10, 20 wt % alumina was studied. The dependences of the formation of microstructure and phase composition on the sintering temperature were established. It was shown that the introduction of additives forming low-temperature melts based on sodium silicates, Na2SiO3 and Na2Si2O5, led to a decrease in sintering temperature by 150–200°C. As a result, dense nanocrystalline materials with a crystal size of 50–200 nm, strength of up to 500 MPa, and sintering temperature of 1300–1400°C were obtained.

Microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites, and effects of ZrO2 crystal structure on mechanical properties, thermal properties, and sintering kinetics

Structural ceramics such as Al2O3 and Al2O3–ZrO2 composites are widely used in harsh environment applications. The conventional sintering process for fabrication of these ceramics is time-consuming method that requires large amount of energy. Microwave sintering is a novel way to resolve this problem. However, to date, very limited research has been carried out to study the effects of different ZrO2 crystal structures on Al2O3–ZrO2 composites, especially on the sintering kinetics, when fabricated by microwave sintering.The microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites was performed in this study. Tetragonal zirconia and cubic zirconia were used as two different reinforcements for an α–alumina matrix, and the mechanical and thermal properties were studied. It was found that Al2O3 experienced a remarkable increase in fracture toughness of up to 42% when t-ZrO2 was added. Al2O3–c-ZrO2 also showed increased fracture toughness. The sintering kinetics were also thoroughly investigated, and the average activation energy values for the intermediate stage of sintering were estimated to be 246 ± 11 kJ/mol for pure Al2O3, 319 ± 71 kJ/mol for Al2O3–c-ZrO2, and 342 ± 77 kJ/mol for Al2O3–t-ZrO2. These values indicated that the activation energy was increased by the addition of either type of ZrO2, with the highest value shown by Al2O3–t-ZrO2.

Properties of TiC and TiN Reinforced Alumina–Zirconia Composites Sintered with Spark Plasma Technique

In this paper, Al2O3–ZrO2 composites with an addition of 20 wt% TiN and 10 wt% TiC were modified. The addition of zirconia in a range from 2 to 5 wt% of the monoclinic phase and 10 wt% of Y2O3 stabilised ZrO2 affected the mechanical properties of the composites. A new type of sintering technique—the spark plasma sintering (SPS) method—within a temperature range from 1575 °C to 1675 °C, was used. Vickers hardness, apparent density, wear resistance and indentation fracture toughness KIC(HV) were evaluated at room temperature. An increase of the sintering temperature resulted in an improvement of Vickers hardness and an increase of the fracture toughness of the tested composites. The tribological properties of the samples were tested using the ball-on-disc method. The friction coefficient was in a range from 0.31 to 0.55, depending on the sintering temperature. An enhancement of the specific wear rate was dependent on the sintering temperature. The mechanical properties of the samples sintered by pressureless sintering (PS) were compared. X-ray diffraction patterns were presented in order to determine the phase composition. SEM microstructure of the tested composites sintered at different temperatures was observed.

The influence of Al2O3 content on Al2O3-ZrO2 composite-textural structural and morphological studies

In this work binary Al2O3-ZrO2 composites with 25, 50, and 75%, w/w Al2O3 were synthesized by the sol-gel method, to find out the better Al2O3 amount that improve the texture, structure, and morphology. The composites presented high surface area, porosity and microcrystalline structure due to high cations dispersion induced by a good intermingling of the components. We found that structure of Al2O3-ZrO2 composites include AlO4 (tetrahedral), AlO5 (pentahedral) AlO6 (octahedral) polyhedral units. An increment of AlO4 and AlO6 species for low Al2O3 amount in the composites was observed. This was possibly related with segregated particles caused by progressive removal of hydroxyl groups. Otherwise, for high Al2O3 amount the fraction of AlO5 species was high, this behaviour was associated with an appropriate distribution of cations within the network of the composites as derived from condensation reactions. A suitable distribution of the Al3+ and Zr4+ cations in the network of the composites is observable by Z-contrast where for high Al2O3 concentrations an homogeneous arrangement was observed. Besides, for low Al2O3 concentrations rods of ZrO2 with an average length at ∼250 nm are observable. Finally, by XPS analysis the non-lattice and lattice oxygen ratio presented similar values for Al50Zr50 composite, associated with the same available vacancies where Al3+ and Zr4+ cations have mayor mobility in the bulk and the superficial of the composite.

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al2O3–ZrO2/Al2O3 ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al2O3–ZrO2 film is smooth and compact, and the interface between the composite Al2O3–ZrO2 film and Al2O3 film is crack-free, which contributes to improving the protective performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al2O3–ZrO2/Al2O3 ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al2O3–ZrO2/Al2O3 ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al2O3 overcoat and composite Al2O3–ZrO2 overcoat.

The new nano-enabled phase map of ZrO2-Al2O3

Rapid development of nanotechnology often requires verification of existing phase diagrams, which were suitable for bulk materials. This work presents a new phase map (phase diagram) for Al2O3-ZrO2 crystalline powders including the role of the nanoscale particles. Al2O3-ZrO2 composites are relevant for industry for applications demanding high hardness. The nanopowders were manufactured via co-precipitation process followed by microwave hydrothermal synthesis (MHS) at 270 °C, drying at room temperature and annealing in the temperature range 300–1500 °C. The phase composition was investigated using X-ray diffraction (XRD) and Rietveld refinement analysis. The grain size and size distribution were calculated using Rietveld refinement analysis and using transmission electron microscopy (TEM). A particular feature of the composites was the nanoisolation, separation of different phases on a nanoscale. This feature limited grain growth during annealing and permitted the phase diagram for a nano-enabled system to be determined, which turned out to be different from that of conventional composites. In particular, considerable solubility of Al3+ in ZrO2 was found for temperatures less than 1000 °C.