Enhancing superplasticity of engineering ceramics by introducing BN nanotubes

Abstract

Introducing carbon nanotubes (CNTs) into polymer or ceramic matrices has been a promising approach to obtain ultra-strong, extra-toughened materials as well as multifunctional composites. Most of the previous work on CNT composites has focused on strengthening and toughening of matrix materials at ambient conditions. However, so far there is a lack of information on the mechanical behavior of these composites at elevated temperature. Recently, single-walled CNTs were found to undergo a superplastic deformation with an appealing 280% elongation at a high temperature (Huang et al 2006 Nature 439 281). This discovery implies the high probability for the potential usage of CNTs as reinforcing agents in engineering high-temperature ceramics with improved ductility. Here, for the first time, we demonstrate that a small addition of boron nitride nanotubes (BNNTs) can dramatically enhance the high-temperature superplastic deformation (SPD) of engineering ceramics. More specifically, 0.5 wt% addition of BNNTs leads to an inspiring brittle-to-ductile transition in Al 2 O 3 ceramics even at a moderate temperature (1300 • C). For Si 3 N 4 ceramics, 0.5 wt% addition of BNNTs could also decrease the true stress by 75% under the same deformation conditions. In contrast, addition of micro-sized or nano-sized BN powders has no or a negative effect on the superplasticity of these ceramics. The underlying SPD-enhancement mechanism is discussed in terms of the inhibition of static and dynamic grain growth of the matrix and the energy-absorption mechanism of BNNTs. The unraveled capability of BNNTs to enhance the SPD behavior will make BNNTs promising components in cost-effective complex ceramics with good comprehensive mechanical properties.

Hydroxyapatite-Nanotube Composites and Coatings for Orthopedic Applications

“…Due to shorter time of sintering, SPS retains the nanostructure and improves the mechanical property of the sintered body [19,[50][51][52][53][54]. In addition, minimal dwell at high temperature causes lesser dissociation of HA into TCP [56][57][58][59][60][61].SPS of HA-CNT has employed temperatures in the range of 900 -1250 °C [42,46] , pressure of 7.5-120 MPa [42,46] in vacuum [41] or argon [31]. The systematic studies on the determination of ideal SPS temperature for HA-CNT system found 1100°C…”

“…Poor wear resistance of HA is one of the shortcomings for its application as orthopedic implant [28,38,59,61,84]. …”

“…Only one study is available on ceramic (Al 2 O 3 and Si 3 N 4 ) based BNNT composites [163]. BNNT introduces high temperature superplasticity in the ceramics by controlled dynamic grain growth and energy absorption mechanism.…”

Network distribution of reinforcements in composites produced by sintering: microstructure formation and influence on consolidation behavior and properties

“…The authors argued that the content and distribution of CNTs in ceramics impact the grain boundary sliding during deformation. Huang et al 52) showed that the presence of boron nitride BN nanotubes in alumina enhanced the superplastic behavior of the composite through the mechanism of inhibition of both static (in the assintered composite) and dynamic grain growth (after compressive deformation) in the ceramic matrix.…”

Superplastic Behavior of Alumina Composites Mediated by Carbon Nanotubes

“…Recently, Huang et al reported that addition of small amount of BN nanotubes (BNNTs) (0.5 wt%) into alumina and silicon nitride ceramics made them more ductile at moderate temperatures than corresponding pristine ceramics [7]. The static grain growth in the as-sintered BNNT/alumina and the following dynamic grain growth after compressive deformation are dramatically inhibited.…”