Reactive Current-Activated Tip-Based Sintering of Ni–Al Intermetallics

Current-activated tip-based sintering (CATS) is a new process that imposes local current-activated sintering conditions to consolidate selected areas of a powder compact/bed through the controlled application of a contacting tip electrode. The process has the ability of achieving very high sintering rates and obtaining complex-sintered geometries through the controlled precision motion of the electrically conductive tip. In this study, the high current densities afforded by CATS are utilized to locally activate a macroscopic combustion synthesis type reaction in compacts of reactive mixtures of nickel and aluminum to rapidly form nickel aluminides. The effect of current intensity on the ignition time, microstructure, homogeneity, and properties of the combustion synthesized products is discussed in this article. It was found that ultra-rapid formation of aluminum-rich intermetallics precedes and contributes to the major ignition event. Moreover, time to ignition was found to decrease with an increase in current intensity, also leading to less homogenous microstructures.