Electrical conduction in initial field assisted sintering stages

Field Activated Sintering Techniques (FAST) are increasingly used to consolidate metal and ceramic powders. They combine application of a pulsed electrical current with external pressure to activate the densification process. The nature of electrical field/current interaction with powder systems is not clear yet. In this regard, in-situ transport measurements and microstructural analyses were carried out during pulsed current application in the FAST processing of Ni powders. Our experimental results were compared with existing electrical conduction theories and observed effects were relatively well explained qualitatively within these theories. Under electrical field it was confirmed that no voltage-current phase-shift occurs at elevated operating interfacial temperatures. For the field situation a higher applied pressure is decreasing the contact instability among particles contacts and of the sintering onset temperature. Microstructural investigations of the FAST-sintered samples indicate rather distribution of the higher density regions and a considerable increase of neck formation above 340 degrees C.