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This work uses in situ transmission electron microscopy (TEM) based micromechanical testing to isolate and quantify the microstructural toughening mechanisms active in nanostructured Al 2 O 3 /GdAlO 3 eutectic samples. The effect of fracture direction across orthogonal sections of the rod-like eutectic was used to reveal the influence of different fracture paths and mechanisms on toughening. The average fracture toughnesses of the rod-like structures in the longitudinal cross-section and transverse cross-section are 2.4 MPa·m1/2 and 2.7 MPa·m1/2, respectively. Multiple samples tested in the longitudinal cross-section show significant R-curve toughening response, and obtain values greatly exceeding the initial values upon crack extension. It is concluded that nanoscale crack bridging induces deflection of the crack path, which leads extrinsic energy dissipation as the crack opens. Micropillar compressions are also performed to investigate the composite's strength. Sample orientation strongly affects the deformation mode and interfacial sliding occurs when the maximal shear stress is parallel to the interface. [ABSTRACT FROM AUTHOR]

This study aims to elucidate the impact of interfacial microstructure and properties on fracture toughness in binary Al 2 O 3 /SmAlO 3 eutectic and its polycrystalline samples via in-situ microcantilever deflection tests. Al 2 O 3 -SmAlO 3 eutectic with semi-coherent heterointerfaces exhibits superior interfacial toughness of 2.85 MPa⋅m1/2 relative to randomly oriented interfaces in Al 2 O 3 /SmAlO 3 polycrystals. SmAlO 3 grain boundaries (GBs) have the lowest toughness of 1.97 MPa⋅m1/2 among all the constituents, i.e. bulk and interfaces. The toughness of eutectic Al 2 O 3 -SmAlO 3 interfaces is intermediate between polycrystalline Al 2 O 3 -Al 2 O 3 GBs and SmAlO 3 -SmAlO 3 GBs. Fracture toughness values of both polycrystalline and eutectic Al 2 O 3 -SmAlO 3 samples obtained by mesoscopic indentation measurements are in the range of 4.2 MPa⋅m1/2to 4.7 MP⋅m1/2, which exceeds all constituent components. Much of the overall fracture toughness of the bulk samples derives from microstructural and geometric energy dissipation mechanisms. [ABSTRACT FROM AUTHOR]

The present work concentrated on a novel one-step pulse discharge plasma melting method for in situ fabricating Al 2 O 3 -ZrO 2 binary eutectic in a short processing time. Al 2 O 3 -ZrO 2 eutectic exhibited well-aligned fibrous and colonial structure with a minimum lamellar spacing of ∼250 nm at the growth rate of ∼176.0 μm/s. The lamellar spacing was well consistent with the inverse-square-root dependence on the growth rate as λ = 2.90 × v − 1 / 2 , and the constant of proportionality of 2.90 was close to 3.32 predicted by the JH eutectic theory. The formation mechanism of Al 2 O 3 -ZrO 2 eutectic on primary faceted-alumina crystals was also proposed. The Al 2 O 3 -ZrO 2 eutectic originated from the faceted Al 2 O 3 primary crystals, which played the leading role in the coupled growth process. The interfacial fracture behavior across the coarse intercolony regions was explored, and the fracture toughness of Al 2 O 3 -ZrO 2 eutectic ceramics was comparable to those achieved by traditional directional solidification. [ABSTRACT FROM AUTHOR]

Sm 2 (Zr 1– x Ti x ) 2 O 7 (0≤ x ≤0.15) ceramics have been fabricated by pressureless-sintering method at 1973 K for 10 h in air. The influence of TiO 2 doping on microstructure and thermo-optical properties of Sm 2 (Zr 1– x Ti x ) 2 O 7 ceramics is investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The partial substitution of Ti 4+ for Zr 4+ results in a significant increase in emissivity at low wavelengths contrasted with undoped Sm 2 Zr 2 O 7 . Sm 2 (Zr 0.85 Ti 0.15 ) 2 O 7 ceramic exhibits a high emissivity of above 0.70 at 1073 K in a wavelength range of 3–16 µm, where the highest value at this temperature is more than 0.90 especially in the wavelength range of 9–14 µm. FT-IR spectra and optical absorption spectra unveil the mechanisms of enhanced emissivity in Sm 2 (Zr 1– x Ti x ) 2 O 7 (0.05≤ x ≤0.15) ceramics in the intermediate infrared range, especially at the wavelengths of 3–8 µm, due to Ti 4+ ion substitution for Zr 4+ ion. [ABSTRACT FROM AUTHOR]

The present work aims to provide fundamental insights into the grain size dependence and mechanical behavior of hot-pressed Al 2 O 3 -ZrO 2 ceramic at its eutectic composition, and further to explore the hardening effect of laser-induced surface nanoeutectic layer. The underlying correlations between densification behavior, grain size distribution and mechanical properties were elucidated. Sintering at 1550 °C promotes the densification without extensive grain growth, and in this case the sample exhibits a critical density of 99.3 %. The average grain size is tailored into a range of 0.6–0.9 μm, and the measured flexural strength and toughness reach 1100 MPa and 11 MPa·m1/2, respectively. The metastable t -ZrO 2 grains indeed play a pivotal role in energy dissipation at the crack tip through crack deflection and branching. In addition, the mechanical behavior is reasonably explained through constructing a multilevel toughening mechanism map associated with grain size distribution of ZrO 2. Particularly, surface nanocrystallized Al 2 O 3 -ZrO 2 eutectic layer with a thickness of 1000 μm free of pores and cracks is achieved by a rapid laser melting process. The outmost laser-modified nanoeutectic layer exhibits a fine cellular structure with an interphase spacing of only 105 nm and a hardness of as high as 26.1 GPa, which provides a promising potential in enhancing significantly the hardness and wear resistance for applications as sliding ceramic components. [ABSTRACT FROM AUTHOR]

Abstract This present work explores initially the feasibility of producing in-situ surface nanoeutectic Al 2 O 3 -ZrO 2 (Y 2 O 3) (SNAZ) ceramics via the oxyacetylene flame remelting (OAFR) process. Singular cellular nanoeutectics consist of nanoscale lamellae, which prevail in the samples formed under different irradiation times. Ultrafine nanoeutectics are achieved by prolonging the irradiation time, and their formation mechanisms associated with eutectic refinement are proposed to obtain a better understanding on the melt thermal history and microstructural inheritance. The enhanced nucleation undercooling is the essential mechanism associated with the microstructural refinement. SNAZ formed by the OAFR-based rapid solidification seem to offer an inexpensive route to realize in-situ microstructure tailoring or surface shaping. [ABSTRACT FROM AUTHOR]

An efficient and flexible chemical co-precipitation method has been used to synthesize nanoscale Al 2 O 3 -GdAlO 3 powders with eutectic composition. The as-synthesized powders exhibit a highly dispersive and homogeneous distribution with an average particle size of 50 nm. The phase transition in the resulting powders strongly depends upon the calcination temperature. GdAlO 3 undergoes complete crystallization after calcination at 1050 °C, however, the diffraction peaks of α-Al 2 O 3 are found at a relatively high calcination temperature of at least 1300 °C. The fully-densified Al 2 O 3 -GdAlO 3 ceramic with eutectic composition obtained by hot pressing the nanoscale powders at 1500 °C exhibits a room temperature flexural strength of 556 MPa, a Vickers hardness of 17.3 GPa and a fracture toughness of 7.5 MPa m 1/2 . The high temperature flexural strength of the as-sintered Al 2 O 3 -GdAlO 3 ceramic is measured to be 515 MPa after bending tests at 1000 °C. [ABSTRACT FROM AUTHOR]

In the present work, microstructural refinement and mechanical response of Al 2 O 3 –ZrO 2 eutectics fabricated by a pulse discharge plasma assisted melting (PDPAM) method were investigated. The solidified microstructure evolves from polygonal eutectic colonies into irregular cellular colonies with increasing the superheating temperature of the melt from 1820 °C to 1900 °C. The average eutectic spacing inside the colonies decreases from 1.80 ± 0.10 μm to 0.25 ± 0.06 μm, and the coarse inter-colonial structure is refined, which is attributed to the increase in undercooling temperature. High-temperature microstructural stability of Al 2 O 3 –ZrO 2 eutectics is improved significantly as contrasted with the as-sintered ceramics. Besides, the load dependence of Vickers hardness for Al 2 O 3 –ZrO 2 eutectics is investigated. [ABSTRACT FROM AUTHOR]

Seven unreported compounds were isolated from dried flower buds of Ochrocarpus longifolius in this study, including an alkaloid ochrocaracid A (1), five coumarins ochrocarpins I (2), J (3), K (4), L (5), and M (6), and one styryl-2-pyranone compound iresinoacid (7) and nine known compounds (8 – 16). All these compounds were found in O. longifolius for the first time. Their structural elucidation was achieved through NMR, HR-ESI-MS, and ECD data. Additionally, a glucose uptake-promoting activity assay revealed that compounds 10 (128.21 μM) and 16 (123.15 μM) increased the glucose uptake capacity of L6 cells by 1.49-fold and 1.48-fold, respectively. These bioactive compounds could be potential candidates for further pharmaceutical applications. Seven undescribed compounds, an alkaloid ochrocaracid A (1), five coumarins ochrocarpins I (2), J (3), K (4), L (5) and M (6), and one styryl-2-pyranone compound iresinoacid (7), were isolated from dried flower buds of Ochrocarpus longifolius. [Display omitted] • Seven undescribed compounds (1 – 7) were isolated from dried flower buds of Ochrocarpus longifolius. • All of these compounds (1 – 16) were found for the first time in O. longifolius. • Compounds 10 and 16 showed glucose uptake-promoting activity. [ABSTRACT FROM AUTHOR]

Abstract The nucleation and epitaxial growth behavior of a novel Al 2 O 3 -ZrO 2 nanoeutectic rapidly solidified from the oxyacetylene flame remelting have been investigated. The nanoeutectic ceramic consists mainly of highly textured cellular structure with an average interphase spacing of 136 nm. Especially, a singular transition mechanism associated with " one-step cellular refining " to " two-step cellular refining " is proposed in a variable region from a coarse irregular to an ultrafine lamellar structure, and the regional undercooling is estimated to be 0.57–2.86 K. The Al 2 O 3 phase nucleates as the leading phase in the rapidly solidified structure according to a quantitative calculation of nucleation rate. The cellular eutectic exhibits with a tilted feature, where its cellular growth deviates from the heat flow direction to a preferred growth orientation. [ABSTRACT FROM AUTHOR]

In the present work, Al 2 O 3 -GdAlO 3 oxide nanopowders with eutectic composition of 77:23 (in molar ratio) were prepared via a chemical co-precipitation method. α-SiC particles were then incorporated with different volume fractions of 10, 15 and 20 vol% into the oxide powders. Al 2 O 3 -GdAlO 3 –SiC ceramics were hot-pressed at different sintering temperatures to obtain fully densified bulk ceramics. The as-sintered composites consist mainly of α-Al 2 O 3 , GdAlO 3 and α-SiC phases, and exhibit a dense and uniform microstructure. The GdAlO 3 grains are entangled with α-Al 2 O 3 grains as indicated by SEM observations. SiC nanoparticles are found within the interior of both α-Al 2 O 3 and GdAlO 3 grains or at the interfaces between entangled α-Al 2 O 3 and GdAlO 3 . With increasing the SiC content from 10 to 20 vol%, the high-temperature flexural strength of Al 2 O 3 -GdAlO 3 -SiC ceramics increases from 567 to 616 MPa, and the Vickers hardness increases from 17.5 to 19.5 GPa, while the fracture toughness of Al 2 O 3 -GdAlO 3 -SiC ceramics increases from 8.20 to 9.28 MPa m 1/2 , which is significantly improved with respect to that (7.5 MPa m 1/2 ) of unmodified Al 2 O 3 -GdAlO 3 ceramic. The toughening mechanisms of Al 2 O 3 -GdAlO 3 -SiC ceramics are attributed to crack deflection, pinning and bridging, and bifurcation due to the presence of SiC nanophases observed from the indentation. [ABSTRACT FROM AUTHOR]