A comprehensive study on flash sintering of anatase and rutile polymorphs-containing titania nanopowder: Phase and microstructure development

Flash sintering has proven to be a novel and cost-efficient technique that enables the successful processing of dissimilar materials. The present work investigated how sintering under electric field input progresses in commercial anatase (A) plus rutile (B) polymorphs containing titania. Both the phase evolution and sintering dynamics were highly dependent on the strength of the field, the application of which led to (A + R) → R → flash at low fields while promoting (A + R) → flash at high fields. A temperature postponement of flash was verified at low fields, as the event was preceded by the A → R transformation, which was responsible for a detectable peak in the thermal spectra of the current. The processing temperature, applied electric field (E), and onset flash sintering temperature ( ${\mathit{T}}_{\mathbf{f}\mathbf{u}\mathbf{r}\mathbf{n}}^{\mathbf{f}\mathbf{l}\mathbf{a}\mathbf{s}\mathbf{h}}$) combine well into a phase diagram graph that summarizes the phase development that applies to this material. In addition, high-density bodies in the rutile phase were ultimately produced after flashing under a suitable current density, regardless of the field strength considered. Both the flash sintering temperature and average grain size (AGS) decreased with increasing field. In line with this, we demonstrate the existence of a direct link between the grain size and the sample sintering temperature, which is consistent with the classical grain growth model.