Abstract
M.Tech. (Metallurgy Engineering)
The demand for superalloys that are corrosion-resistant, cost-friendly, and faster to fabricate is critical in advanced technologies, such as in the marine environment. In this study, pure NiAl powder was reinforced with 0.5 and 1.0 wt.% of carbon nanotubes (CNT). Spark plasma sintering of NiAl reinforced with carbon nanotubes (CNT) was conducted using a conventional and a hybrid spark plasma sintering furnace. X-ray diffractometer (XRD) and a field emission scanning electron microscope (FESEM) equipped with an energy dispersive spectrometer (EDS) were used to examine the phase constitution and microstructure of the sintered and corroded alloys. Pure NiAl, 0.5 and 1.0 wt.% CNT alloys were assessed for corrosion resistance in 3.5%-Na2SO4 and 3.5%-NaCl through electrochemical techniques; open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization. The Tafel extrapolation technique was conducted to determine the corrosion potentials (Ecorr) and corrosion current densities (Icorr). Faraday's law was employed to determine the corrosion rate of the three alloys in two electrolyte solutions (NaCl and Na2SO4). The electrochemical characterization of the NiAl alloys with various CNT reinforcements revealed that the best corrosion resistance was obtained at the NiAl reinforcement of 0.5 wt.% CNT while the 1.0 wt.% CNT reinforcement of NiAl gave the lowest corrosion rates, thus poor corrosion resistance. The characterization of corroded alloys via SEM and XRD revealed Al2O3 as one of the main oxides acting as a passive layer on the alloy specimen surface.