Localized current activated sintering of titanium nickelides

Includes bibliographical references (p. 88-93).This research thesis discusses the processing of 50 at. % Ni-Ti elemental powders through Ball Milling (a Mechanical Alloying process) route and locally sintering of titanium nickelides via Current-Activated Tip-based Sintering (CATS), a novel sintering process. CATS process facilitates much higher current densities than any conventionally available sintering process, which can bolster rapid sintering and intermetallic phase transformation rates. For the first time CATS was employed to tip-sinter equi-atomic mechanically alloyed Ni-Ti powder system at varying current intensities (50 A -- 100 A) and cumulative current exposure time (1 second -- 100 seconds). The effect of current and sintering time conditions on the evolution of the locally sintered Ni-Ti microstructure and its properties are discussed. Harder Ti2Ni phase shows significant effect on NiTi mechanical properties (i.e. micro-hardness). With increasing current exposure time at constant current intensities shows an enhancement in the sintered process zone. It was discovered that current intensity, cumulative exposure time and distance from the tip/material interface have direct implication to degree of sintering, intermetallic phase transformations, and microstructural properties of titanium nickelides. This research studies displays the full/near full densification of titanium nickelides in extraordinary short times at locations exposed to exceptional ultra-high current densities