Hai-Tao Liu

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.

Synthesis of rod-like ZrB2 powders

Rod-like ZrB2 powders were synthesised at 1500°C in vacuum by boro/carbothermal reduction using ZrO2, B4C and graphite as the starting materials. During the heating process, the ZrB2 grains primarily grow along the c axis to form a rod-like morphology without any heterogeneous catalyst. The final products are pure rod-like ZrB2 particles, which are thought to be promising starting powders to prepare high performance ultrahigh temperature ceramics with unique microstructures such as textured one through tape casting process.

Zrc ceramics incorporated with different-sized SiC particles

ABSTRACT Three different SiC powders with average particle sizes of 0.45, 3.5 and 10u2005µm were used to prepare ZrC-20vol.-% SiC ceramics by hot pressing. The effects of SiC particle size on the densification, microstructure, mechanical properties and thermal properties of ZrC–SiC ceramics were studied. Ceramics prepared from SiC with finer particle sizes exert higher bending strength, hardness and lower thermal conductivity. The ZrC–SiC ceramics with a starting SiC particle size of 3.5u2005µm has relative high fracture toughness than others. Analysis indicates that SiC grain size and the grain boundaries control the thermal conductivity ZrC–SiC ceramics. Ceramics prepared from SiC with the particle size of 10u2005µm exhibits the highest thermal conductivity due to the larger grains and less grain boundaries.

Chemical process and solid solution formation in reactive hot pressed ZrB2-SiC ceramics doped with W

ABSTRACT ZrB2–SiC doped with W was prepared from a mixture of Zr, Si, B4C and W via reactive hot pressing. The fully dense ZrB2–SiC–WB–ZrC ceramic was obtained at 1900°C for 60 min under 30u2005MPa in an argon atmosphere. Reaction path and solid solution characteristics of the starting powders were studied through a series of pressureless heat treatment at temperatures between 700 and 1500°C. The solid solution phases of (Zr, W)B2, (W, Zr)B and (Zr, W)C were formed directly by reactions between the precursors. Homogeneous distribution of solute atoms in solution and the solid solubilities were also studied.