Achieving effective load transfer at the interface between carbon nanotubes (CNTs) and aluminum (Al) is a crucial issue for fabricating high-performance CNTs reinforced Al matrix (CNT/Al) composites. In this work, CNT/Al composites with different Ti additions and the compared materials were prepared by powder metallurgy . Micro-sized Ti particles in which CNTs are well-dispersed firstly circumvent the difficulty of CNT dispersion, and subsequently act as nucleation site for sandwiched TiAl 3 layers that lock the dispersed CNTs in place and improve the CNT-Al interface bonding. Additionally, Ti addition not only allows modification of the dispersed CNTs but also enhances the strength of the composites by enhancing the load-bearing capacity of the CNTs through in situ formation of nano-sized titanium carbide (TiC). This work provides a new approach to improve the load transfer efficiency of CNTs by strengthening the interface bonding for fabricating high strength CNT/Al composites.
Porous TiAl 3 intermetallics were synthesized from Ti-75 at.% Al elemental powder mixtures using an energy-saving and rapid reactive method of thermal explosion (TE). The results demonstrated that the actual temperature of the compact climbed rapidly from 673 °C to 1036 °C within 24 s, indicating that an obvious TE reaction occurred during sintering process. The video graphs suggested that the TE in Ti–Al system behaved instant occurrence and overall heating whether from axial or radial direction. The silver wires and NaCl particles that pressed on the surface of the sample disappeared due to the heavy heat released during TE reaction. Only pure TiAl 3 phases were synthesized in TE products and the open porosity of 55.4% was easy to obtain. After high-temperature treatment at 1000 °C, large amounts of sintering-neck formed and then improved the compressive strength of porous TiAl 3 materials. Moreover, the mass gain curve of porous TiAl 3 intermetallics oxidized at 650 °C for 120 h exhibited the parabolic oxidation rate law. XPS analysis confirmed that the strong O 1s peak was 531.4 eV which was the typical binding energy of Al 2 O 3 . Therefore, the excellent oxidation resistance of porous TiAl 3 foams would be considered as good candidate materials for prolonging the service life at high temperatures.
In this study, Si-alloyed porous TiAl₃ intermetallic compounds were synthesized through an efficient and rapid self-exothermic reaction. The gas permeability and pore structure of the samples were quantitatively analyzed using 3D-X-ray microtomography (3D-XRM). Combined with a self-made "visual window" and real-time temperature curves, the entire green compact exhibited a distinct and uniform exothermic behavior at every moment. The addition of Si element transformed the intense solid-liquid reaction into a relatively gentle two-step sintering process. The results indicated that an appropriate amount of Si can significantly enhance the uniformity of pore structure and increase the mechanical properties by nearly five times. Meanwhile, the oxidation kinetics curves revealed that the oxidation process was divided into an initial rapid oxidation stage and a subsequent slow oxidation stage, and the mass gain ratio of the samples gradually decreased with the increase of Si content. Furthermore, a dense Al₂O₃ oxide layer can form on the surface of skeleton at high temperatures, effectively hindered the inward diffusion of oxygen and provided a feasible design concept for achieving porous TiAl₃-based composites with high porosity and excellent performance.
Porous NbAl 3 /TiAl 3 with adjustable porosity was prepared by the thermal explosion (TE) mode of combustion synthesis (CS). This was achieved by using NaCl as temporary space holder, which was completely removed from specimens before TE reaction. The combustion image of this process provided the visual evidence for the observation of TE. The temperature profile, course of reaction as well as the effect of NaCl content on the phase composition, pore morphology and open porosity of porous NbAl 3 /TiAl 3 were investigated. The results showed that the addition of TiH 2 prevent the samples from cracking and deforming, and in situ synthesis of NbAl 3 /TiAl 3 intermetallic composites. The interconnected channel was formed when using NaCl as space holder, which made the porous NbAl 3 /TiAl 3 an open cellular structure. The open porosity can be improved from 48% to 79% by adding 70 vol.% NaCl particles. The small pores (<20 μm) in porous NbAl 3 /TiAl 3 originated from the intergranular pores in green compact and the decomposition of TiH 2 , whereas the large pores (200–300 μm) were attributed to the replication of NaCl particles. This leachable space holder route provides a flexible way to adjust the pore morphology and porosity to multifarious applications.
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