RESUMEN
The effectiveness of the room-temperature strengthening strategy for aluminum (Al) is compromised at increased temperatures due to grain and precipitate phase coarsening. Overcoming the heightened activity of grain boundaries and dislocations poses a significant challenge in enhancing the high-temperature strength through traditional precipitation strengthening. This study presents novel strengthening strategies that integrate intergranular reinforcements, intragranular reinforcements, refined grain, and stacking faults within an (Al2O3+Al3Ti)/Al composite prepared using sol-gel and powder metallurgy technology. Excellent high-temperature tensile properties are achieved; also, a remarkable fatigue performance at increased temperatures that surpasses those of other existing Al alloys and composites is revealed. These superior characteristics can be attributed to its exceptionally stable microstructure and the synergistic strengthening mechanisms mentioned above. This work offers new insights into designing and fabricating thermally stable Al matrix composites for high-temperature applications.
RESUMEN
Lacking macroscopic plasticity severely limits structure applications of bulk metallic glasses (BMGs). In general, particle-reinforced BMGs have an enhanced ductility but show reduced strength, whereas body-centered-cubic CuZr phase (B2 phase)-reinforced bulk MGs display improved ductility and strength. The underlying reason for the improvement in B2 phase-reinforced BMGs is still ambiguous. Herein, the atomic arrangement in Cu48Zr48Al4 BMGs with and without the B2 phase under tensile deformation is studied using molecular dynamics simulation. Different from pure MG where shear transformation zones (STZs) are activated along the same direction to form the domain shear band, STZs in the B2 phase-reinforced MG are activated along different directions disturbing the formation of a domain shear band. More plastic deformation and increased stress are allowed because of the phase transformations of B2 phases. The revealed deformation mechanism of B2 phase-reinforced MGs enables us to design heterogeneous structures with excellent strength and toughness.
RESUMEN
Recently, wearable multifunctional fibers have attracted widespread attention due to their applications in wearable smart textiles. However, stable application, large-scale production and more functions are still the greatest challenges for functional fiber devices. In this study, wearable multi-functional coaxial fibers with oriented carbon nanotubes (CNTs) were achieved for the first time coaxial wet-spinning with rotating coagulation bath. Specifically, the cellulose solution can be regenerated in the coagulation bath and the CNTs dispersion will be oriented under the rotating force. The synergy between hydrogen bonding and van der Waals interaction enhance the mechanical strength of coaxial fibers. Especially, CNTs can prevent the rotation of the cellulose chain and the bending of the glycosidic twist angle at the atomic scale as indicated by molecular dynamics (MD) simulations. When the fibers are strained, the cellulose sheath will drive the movement of CNTs, causing changes involving the effective contact area and number of conductive paths. Therefore, the high electrical resistance response change enables the as-obtained coaxial fibers to exhibit a great potential in wearable strain sensors. Furthermore, coaxial fibers can be made into electric heaters based on the Joule heating principle. The heating temperature reaches more than 160 °C within 6 s at 10 V, which is of a great value for large area flexible heaters. Besides, the coaxial fibers can further be used as temperature-sensitive devices to accurately perceive the external temperature. Therefore, the scalable synthesis of multifunctional coaxial fibers is significantly expected to provide a platform for the large-scale production of multifunctional wearable intelligent textiles.
RESUMEN
In this study, effects of sintering temperature and TiH2 on the sintering process of Cu are investigated. During sintering, the oxide in Cu decomposes and generates oxygen, which can become trapped in the material forming closed pores. Therefore, this results in low sintered density. Sintering behavior of Cu can be significantly improved by adding 0.5 wt.% TiH2 which decomposes during sintering, producing hydrogen and effectively reducing the oxide in Cu. Although gas products of the reduction reaction may still be trapped inside the close pores formed near the TiH2 particles and handicap the sintering of Cu, an isothermal treatment at 650 °C can avoid forming close pores. This allows reaction products to dissipate freely from the sample, subsequently increasing its sintered density.