Flash sintering with current rate: A different approach

The original flash sintering experiment was carried out by applying an electric field, and switching to current control at the onset of the flash, signaled by a rise in conductivity. Here, we consider experiments where the experiment is controlled from the very start, by injecting current, which is increased at a constant rate. The current rates are varied from 50 mA/min to 5000 mA/min. The experiment is continued until, in all cases, the current density reaches 100 mA/mm 2 . The total duration of the experiment ranged from approximately 7 seconds to 700 seconds. The following comparisons to the earlier voltage‐to‐current experiments are noted: (a) in both instances, the onset of the flash is signaled by an unusual rise in conductivity; however, since the power supply remains in the current control mode, the increase in conductivity is manifested by a drop in the voltage generated across the specimen; (b) the blackbody radiation model is modified to include the energy absorbed in specific heat, in order to determine the time‐dependent change in temperature as the current is increased—this correction is particularly significant at the very high current rates; (c) sintering occurs continuously, reaching full density, in all instances, when the current density reaches ~100 mA/mm 2 ; and (d) these early experiments suggest that the current‐rate experiments yield fine‐grained microstructure across the entire gauge section of the dog‐bone specimen, presumably because the highly transient conditions of voltage‐to‐current flash experiments are sidestepped. The experiments were carried out on 3 mol% yttria‐stabilized zirconia.