Search

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]

Li 7– x La 3 Zr 2– x Ta x O 12 (0 ≤ x ≤ 1) ceramics were prepared by pressureless sintering at 1230 °C in air. XRD, SEM and Impedance test were used to characterize the crystal structure, microstructure and electrical performance of Li 7– x La 3 Zr 2– x Ta x O 12 ceramics. According to XRD data, the specimens with x ≥ 0.2 sintered at 1230 °C for 1 h exhibit a cubic garnet structure without impurities. The Ta-doped specimens sintered at 1230°C for 1 h show high relative density of 91.6%–93.9%. Ta doping has a certain effect on the Li vacancy concentration, lithium arrangement, movable Li+ concentration and microstructure of the LLZO ceramic. The Li 6.6 La 3 Zr 1.6 Ta 0.4 O 12 ceramic sintered at 1230°C for 1 h has the highest total conductivity of 6.01 × 10–4 S·cm–1 at room temperature and the lowest activation energy of 0.27 eV. [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]

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]

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]