Flash Sintering of Tungsten at Room Temperature (without a Furnace) in <1 Min by Injection of Electrical Currents at Different Rates

Sintering of tungsten nominally requires several hours at ultrahigh temperatures. We show this refractory metal can be sintered quickly by direct injection of current into dog bone shaped specimens. The current rate was varied from 10 A s-1 (fast) to 0.1 A s-1 (slow), leading to sintering in 2-200 s, respectively. Sintering occurred at the same current density, regardless of the current rate. In all instances, the samples sintered when they reached 1000 degrees C. The phenomenological behavior of flash sintering of metals is described by three stages: an incubation time followed by electroluminescence, and finally by abrupt sintering to full density. It is conjectured that rapid sintering is instigated by the formation of Frenkel pairs (vacancies and interstitials), as well as electrons and holes. The point defects accelerate mass transport, whereas electrons and holes recombine to form photons. Calorimetric measurements show an endothermic reaction attributed to the creation of defects. Estimates suggest an unusually large concentration of Frenkel pairs. PS: Flash sintering is different than electro-discharge-sintering where a capacitor is discharged in a few milliseconds to sinter a metal. Here, instead of dumping large amount of energy at once, a power supply is programed to control the rate of current injection.