Abstract:

Age hardenable 2014 aluminum alloys and composites containing 0.10 and 0.15 volume fractions of alumina particles (VFAP) have been solutionized at 540 and 550 °C for up to 20 hours. The solutionized samples, heat treated for 5 and 20 hours, have been subjected to room temperature rolling until cracking develops. The work hardening curves have been compared to determine the effect of solutionizing time on the rolling characteristics from both hardness and the microstructural evolution points of view. Solutionizing at two different temperatures results in differences in the extent to which the composites can be rolled until fracture. The microstructural characterization by TEM has been performed to understand the room temperature rolling behavior.

Abstract:

High-temperature ceramics, such as silicon nitride, are considered the best-suited materials for use in extreme environments because they posess high melting temperatures, high strength and toughness, and good thermal shock resistance. The goal of this research is to create bulk multifunctional high-temperature ceramic nanocomposites using single-wall carbon nanotubes in order to tailor electrical and thermal conductivity properties, while also enhancing the mechanical properties of the monolith. Colloidal processing methods were used to develop aqueous single-walled carbon nanotube (SWNT)-Si3N4 suspensions that were directly fabricated into bulk parts using a rapid prototyping method. High-density sintered nanocomposites were produced using spark plasma sintering, at temperatures greater than 1600 °C, and evidence of SWNTs in the final sintered microstructure was observed using scanning electron microscopy and Raman spectroscopy. The multifunctional nanocomposites show exceptional fracture toughness (8.48 MPa-m^1/2) properties and was directly measured using conventional fracture toughness testing methods (ASMT C41 ). Our results suggest that the use of SWNTs in optimized sintered ceramic microstructures can enhance the toughness of the ceramic by at least 30% over the monolith. In addition, the observation of hallmark toughening mechanisms and enhanced damage tolerance behavior over the monolith was directly observed. The nanocomposites also measured for reductions in electrical resistivity values over the monolith, making them high-temperature electrical conductors. These novel nanocomposites systems have enhanced electrical conductivity, and enhanced toughness over the monolith which make them unique high-temperature multifunctional nanocomposites.