Haibin Zhang

Effect of alumina dopant on transparency of tetragonal zirconia

Aiming to characterize the effect of alumina dopant on transparency, powders of yttria stabilized tetragonal zirconia doped with alumina (TZ-3Y-E) are used as starting material to fabricate transparent tetragonal ZrO2 by high-pressure spark plasma sintering (HP-SPS). However, low transparency of the resultant TZ-3Y-E specimens does not suggest a beneficial effect of alumina dopant although nanometric grains and high density have been achieved. The mechanism is analyzed by comparing with the results of as-sintered yttria stabilized tetragonal zirconia without alumina dopant.

Effect of sintering temperature on optical properties and microstructure of translucent zirconia prepared by high-pressure spark plasma sintering

Abstract Aiming to characterize the effect of sintering temperature on transparency of zirconia, we have evaluated the optical properties and microstructure of translucent cubic zirconia prepared by high-pressure spark plasma sintering (SPS) at 1000–1200 ○C. Color centers (oxygen vacancies with trapped electrons) and residual pores were primary defects in the samples. In SPS samples, the total forward transmittance and in-line transmittance are mainly affected by color centers with a limited contribution from residual pores; in contrast, the changes in reflectance are only related to the porosity. The amounts of color centers and residual pores increase with sintering temperature that reduces the total forward and in-line transmittance of the as-sintered zirconia. Annealing in oxidizing atmosphere improves the total forward and in-line transmittance. During the annealing, the concentration of color centers decreases but the porosity increases.

Preparation, texturing and mechanical properties of ZrB2–WSi2 ceramics via reactive hot pressing and hot forging

Abstract ZrB2–WSi2 ceramics with platelet shaped ZrB2 grains were fabricated via reactive hot pressing by the reaction of Zr, B, W and Si. Hot forging was then used to form a textured microstructure in the ceramics. The ceramics obtained by reactive hot pressing demonstrated higher flexural strength than the corresponding ZrB2–MoSi2 ceramics in our previous study, owing to the moderate platelet ZrB2 grain size and the intrinsic properties of WSi2. During hot forging, the platelet ZrB2 grains rotated and rearranged orderly under the pressure, forming textured microstructure with anisotropic properties; however, there is a decrease in flexural strength, owing to the excessive large grain growth during the high temperature hot forging process.

Study on the crystal structure of (Gd2−xCex)Ti2O7 (0 ≤ x ≤ 0.8) pyrochlore

Synthesis, characterisation and crystal structure analysis studies of oxides in (Gd2−x Cex)Ti2O7 series have been reported, Ce3+ used as a surrogate for Pu3+ because they have similar physical and chemical properties. In the present report, a series of pyrochlore-type crystal with composition (Gd2−x Cex)Ti2O7 (0u2009≤u2009xu2009≤u20090.8) were successfully synthesised by the solution combustion followed by high temperature calcining. The phase purity and crystal structure of samples were investigated by X-ray diffraction analysis as well as Rietveld refinement. It was observed that the solubility of Ce3+ in the lattice of Gd2Ti2O7 pyrochlore is 39.62u2005mol.-%. The calculated lattice parameters and the simulated XRD patterns of (Gd2−x Cex)Ti2O7 (xu2009=u20090, 0.5, 1) were obtained based on the density functional theory. The results of theoretical calculation are quite consistent with the results of the experiment. Additionally, the grain size and the visual information about the microscopic structure of the (Gd2−x Cex)Ti2O7 crystals were obtained by transmission electron microscopy.

Microstructure and mechanical properties of in-situ hot pressed (TiB2 + SiC)/Ti3SiC2 composites with tunable TiB2 content

Without impurity phases detected, fully dense (TiB2u2009+u2009SiC)/Ti3SiC2 composites have been successfully synthesised by in-situ reaction hot pressing. The effect of TiB2 content on phase composite, sintering properties, microstructure, and mechanical properties of the composites were thoroughly investigated. With TiB2 content increasing from 0 to 50u2005vol.-%, the flexural strength increases first and then decreases, whereas fracture toughness, hardness and modulus show a linear increase. The maximum strength of 826u2005MPa was obtained at 20u2005vol.-% TiB2. On the whole, the (TiB2u2009+u2009SiC)/Ti3SiC2 composites exhibit a superior comprehensive mechanical properties superior to other reported Ti3SiC2-based composites reinforced by singular reinforcement. The significant strengthening and toughening effect induced by the in-situ incorporated TiB2 can be ascribed to the unique properties of TiB2 and the synergistic action of many mechanisms including particle reinforcement, pulling out of grains, crack deflection and grain refinement strengthening.

Spark plasma sintering of damage tolerant and machinable YAM ceramics

Single-phase Y4Al2O9 (YAM) powders were synthesized via solid-state reaction starting from nano-sized Al2O3 and Y2O3. Fully dense (99.5%) bulk YAM ceramics were consolidated by spark plasma sintering (SPS) at 1800 °C. We demonstrated the excellent damage tolerance and good machinability of YAM ceramics. Such properties are attributed to the easy slipping along the weakly bonded crystallographic planes, resulting in multiple energy dissipation mechanisms such as transgranular fracture, shear slipping and localized grain crushing.