Modeling of flash sintering of ionic ceramics

Abstract

A fundamental understanding of the influence of defects in ionic ceramics at the atomic, microstructural, and macroscopic levels, before, during, and after the flash sintering event is key to the development of ceramic processing operations that lead to fast, low cost, and environmentally safe fabrication of materials. The observed phenomenology of the flash process encompasses multiple time and length scales and has resulted in a wide variety of what sometimes appears to be contradictory explanations. This article summarizes the latest developments on the modeling and simulation of flash sintering, specifically those related to the understanding of the equilibrium and kinetic properties and the corresponding microstructural evolution of ionic ceramics. Challenges and opportunities in the development of theoretical analyses that include unidentified multiphysical effects are discussed, as they pertain to the processing of technologically relevant ceramic materials for advanced structures and devices.

Pressure‐assisted flash sintering of ZnO ceramics

“…According to the changing trend of the macroscopic temperature (except for the experiment performed at 2 MPa) and resistance, that is, experiments with higher pressure have lower sample temperature and resistance as shown in Figures 2B, 3 and 4B, a potential mechanism can, therefore, be considered which is that the pressure changes the behavior of interparticle contacts 19,26,41 . Due to the mechanical action of the pressure, more interparticle contacts formed at higher pressure during the initial stage, and the higher pressure improves the interparticle contacts during the intermediate and final stages, thereby reducing local resistance 19,26,41,67 . This results in a lower local temperature between the particles under higher pressure, resulting in a lower level of grain boundary diffusion, especially for ZnO with electronic conduction with significantly enhanced conductivity at particle surfaces 50 .…”

Flash Sintering in Metallic Ceramics: Finite Element Analysis of Thermal Runaway in Tungsten Carbide Green Bodies

“…In the present work, the flash sintering of pure WC nanopowders was modelled at the macroscopic scale [10] by coupling the equations governing the heat generated by the electric current with those of the heat transfer in solids. Three types of heat losses were considered: (i) conductive heat flux through materials adjacent to the WC sample (zirconia die and molybdenum/copper electrodes), (ii) convective heat flux between the hot surfaces and surrounding air with a heat transfer coefficient h ¼ 5 W/(m 2 K) and (iii) radiative heat flux with the emissivities reported in Table 1.…”

“…This discrepancy will be analysed in detail in the following section, introducing the concept that a powder compact does not behave like a homogeneous material when it is crossed by an electric current. Heat is not generated homogeneously, as simulated by FEM, but it is localised in the region of higher resistance, like particleeparticle contacts [10,24].…”