Description
This thesis investigates the effect of varying Process Control Agent (PCA) on the Electrically Activated Reactive Synthesis (EARS) of Nickel Aluminide (Ni3Al) – Carbon Nanotube (CNT) composites. The effect of PCA was investigated in conjunction with reaction characteristics, developed microstructure, and material properties. Material characterization was conducted using qualitative and quantitative X-Ray Diffraction (XRD), particle size analysis, field emission scanning electron microscopy (FESEM), energy dispersive X-Ray spectroscopy (EDX), and Microhardness testing. As expected, an increase in PCA (from 1 wt% to 5 wt% PCA) lead to an overall decline in Ni-CNT composite particle size following mechanical milling. Additionally, a clear trend of decreasing dislocation density with an increase of PCA was noted. Following EARS processing, the highest conversion to Ni3Al and lowest porosity were achieved when the percolation threshold of aluminum powder within the Ni-CNT/Al powder compact was met (critical in allowing the spreading of the aluminum phase during the reaction). A clear preference for rounded powder morphologies (as opposed to flake-like morphologies) is also shown to improve the hardness, porosity, and Ni3Al conversion of the compacts. Lastly, a novel Electrically Activated Reactive Forging (EARF) process was introduced to promote a less porous microstructure and a greater microhardness. While porosity was decreased, loss of heat to the steel tooling under high pressure resulted in a decline in the combustion temperature leading to less Ni3Al conversion than the compacts synthesized without forging.
