Description
This thesis investigates nickel-based intermetallics and nickel-based carbon nanotube (CNT)-reinforced intermetallic composites created from elemental powders. Specifically, the following powder mixtures were investigated: Ni-Al, Ni-B-Al, Ni-CNT-Al, Ni-B-CNT-Al, and Ni-Ti-CNT. Mechanically activated Ni-Al, Ni-B-Al, Ni-CNT-Al, and Ni-B-CNT-Al powder mixtures were reacted using electrically-activated reactive synthesis (EARS). The effects of boron and CNT additives were investigated with respect to the reaction characteristics, developed microstructure, and properties. Boron and CNT reinforcements were shown to slightly decrease the combustion temperature. Multiphase microstructures were observed in all reacted products which included Ni3Al, NiAl, Ni2Al3, Ni5Al3, and NiAl3. The microhardness was shown to increase with both boron and CNT additions, with measurements exceeding 297 HV. A novel electrically-activated forging process is introduced for the first time. Termed electro-combustion forging, this process was used to electrically react and forge Ni-Ti-CNT to forging strains of 0.50, 0.65, and 0.75. Reacted products contained macroscopic pores that were seen to decrease in size and area with increased forging strain. The majority of the reacted products consisted of highly dense regions with porosities as low as 0.3 %. Depending on the forging strain, the resulting microstructures consisted of NiTi, Ni45Ti55, Ni55Ti45, and NiTi2 intermetallic phases. Microstructural refinement was observed with an increase in forging strain, which helped contribute to microhardness measurements exceeding 650 HV.
