Richard Todd

© 2019 The Authors A novel building block material for the generation of non-brittle ceramic composites consisting of micron-sized alumina platelets homogeneously coated with multi-wall carbon nanotubes (MWCNTs) bound to their surface is described. The MWCNT phase is grown in situ from immobilised metal catalyst particles using chemical vapour deposition techniques. In-depth Raman and scanning electron microscope studies revealed that this approach solves the typical issue of MWCNT-agglomeration in ceramic matrices and paves the way to excellent control over MWCNT purity and concentration within the resulting composite material. Moreover, we show that the preparation of the catalyst is the most important factor for the generation of uniformly distributed MWCNTs of high-quality on these platelets. With these MWCNT-coated alumina building blocks, we have manufactured nacre-like biomimetic composites using spark plasma sintering. The resulting composites are electrically conductive and three-point bending tests show a transition from brittle/catastrophic failure to graceful failure, holding great promise towards multifunctional, tough and strong lightweight ceramic composite manufacturing.

© 2016 Elsevier Ltd The effects were investigated of the starting particle size (i.e., nanometer or submicrometer powders), content of Y3Al5O12 additives (YAG; in the range 5–20 wt.%), and difference of size scales between the two particle types on the liquid-phase assisted flash sintering of SiC from powder mixtures prepared by aqueous colloidal processing. It was found that flash sintering benefits from the refinement of the particles size, the increase in additive content, and the smaller size scale of the particulate additive. It was also found that under the present flash sintering conditions (i.e., 900 °C furnace temperature, 13 A current, and 50 s in flash state) the resulting ceramics are, despite the formation of liquid phase, porous to a greater or lesser extent, and exhibit decreasing porosity gradients from their surface to the centre. These observations are rationalized to extract guidelines for powder batch design contributing to the pressureless ultrafast sintering of non-oxide advanced ceramics.

© 2016 Elsevier Ltd. Fully-dense B4C-based ceramics were fabricated using Ti-Al intermetallics as sintering aid by Spark Plasma Sintering at a low temperature of 1700 °C whilst applying 32 MPa uniaxial pressure. The influence of the intermetallic additions on the phase composition, morphology and mechanical properties of the ceramics were investigated. The intermetallics flowed and react with B4C to form a three-phase composite containing B4C, TiB2 and Al4C3 during the transient liquid phase sintering process. The TiB2 and Al4C3 particles were located on the boundaries between B4C grains and effectively inhibited the growth of B4C, which improved the mechanical properties. Good bonding between B4C and the phases formed was confirmed by TEM analysis. The specimens with 5 wt.% Ti-Al provide an attractive combination of homogeneous morphology and excellent mechanical properties, including a Vickers hardness of 33.5 ± 0.4 GPa, a flexural strength of 506 ± 16 MPa and a fracture toughness of 5.5 ± 0.1 MPa m0.5.