Reactive current activated tip-based sintering of nickle aluminides

Includes bibliographical references (p. 76-80)Current Activated Tip-based Sintering (CATS) is a new process for the powder-based manufacturing of macro, micro and possibly nano-scale features and shapes. CATS enables the selective sintering of powders by localizing current activation conditions through an electrically conducting small tip (either in the stationary or moving mode). This thesis presents for the first time experimental results on the CATS of reactive mixtures of Ni/Al powder to form nickel aluminide intermetallics. Investigations on the effect of electric current and the reaction characteristics are discussed. The effect of green density on localization effects was investigated. The use of CATS to trigger a macroscopic self-propagating high-temperature synthesis (SHS) process was investigated. Electric current intensity was found to have a pronounced effect on ignition time and whether or not a reaction would take place. The resulting microstructures and properties were also dependent on current intensity. The effect of current exposure time on the pre-ignition microstructure evolution was also investigated. Results show that aluminum-rich intermetallics locally form prior to the SHS reaction which in turn contribute to the ignition process in addition to Joule heating effects. Overall, the results prove that reactive CATS can be used to locally trigger a current-activated macroscopic combustion synthesis process in Ni-Al compacts of reactive powder mixtures