We investigated the reinforcing effect of supersaturated Al-C phases on the mechanical properties of Al/C60 composites produced via powder metallurgy followed by thermal treatment. We controlled the fractions of C60-fullerenes, nano-scale carbides, and Al-C supersaturated phases in the Al/C60 composites by adjusting the heat-treatment temperature and duration. Furthermore, we examined the contribution of each phase on the elastic and plastic behavior of the composites using scanning acoustic microscopy (SAM) and hardness measurements. After heat treatment, a supersaturated Al-C phase and an Al carbide were formed in the Al/C composites by decomposition of individually dispersed C60. This led to enhancement of the hardness and elastic modulus of the Al/C composites heat-treated at 450 and 500 °C, while these properties were reduced in the 650 °C heat-treated composite. Notably, the 500 °C heat-treated composites showed significantly high hardness and elastic modulus (approximately 250 Hv and 77.8 GPa, respectively) owing to the substantially large contribution of the supersaturated Al-C phases, which was theoretically calculated to be 851 GPa/vol% and 227 GPa/vol%, respectively. This is possibly because the well-dispersed C in the atomic scale changed the elastic bonding characteristics of the metallic bonds between the Al atoms.
In this study, 3D-printable flexible piezoresistive composites containing various amounts of cilia-like hybrid fillers were developed. In the hybrid fillers, micro-scale Cu particles with a 0D structure may allow them to easily disperse into the flexible TPU matrix. Furthermore, nanoscale multi-walled carbon nanotubes (MWCNTs) with a high aspect ratio, present on the surface of the Cu particles, form an electrical network when the polymer matrix is strained, thus providing good piezoresistive performance as well as good flowability of the composite materials. With an optimal hybrid filler content (17.5 vol.%), the 3D-printed piezoresistive composite exhibits a gauge factor of 6.04, strain range of over 20%, and durability of over 100 cycles. These results highlight the potential applications of piezoresistive pressure sensors for health monitoring, touch sensors, and electronic skin.
In this study, nanoporous high-entropy alloys (HEAs) were fabricated by chemically de-alloying aluminium atoms in mechanically alloyed HEAs. In addition, the effect of alloy composition, compositional uniformity, and porosity of the HEA precursors on the pore structures of the final HEA foams was investigated. Aluminium was successfully de-alloyed only for Ni-free HEAs because of the low mixing enthalpy of Ni and Al. For HEAs containing pre-existing microscale pores, aluminium atoms were readily de-alloyed because the pores opened pathways for NaOH, thereby resulting in hierarchical micro-nanoporous structures in the final foams. For denser HEAs with better compositional uniformity, homogeneous nanoporous structures were revealed in the final foams.
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