Promoting core/surface homogeneity during flash sintering of 3YSZ ceramic by current path management: experimental and modelling studies

During flash sintering (FS) of ceramics, the heat loss by surface radiation is the main cause of temperature gradient between core and surface, which induces inhomogeneity in microstructure. To solve this problem, the judicious designing of sample geometry and electrodes configuration is proposed. Experimental and simulation results show that the application of dogbone shape, forked electrodes, and lower cross-section aspect ratio effectively shifts the current path in 3YSZ samples from core to near-surface during FS, compared to bar-shape samples with a single electrode at each end. Consequently, the temperature distribution becomes more uniform throughout the 3YSZ sample, resulting in increase in relative density from 92.7 % to 99.7 % and improved core/surface homogeneity in microstructure. These optimizations enable 3YSZ ceramics to obtain significant increase in flexural strength from 1203 ± 17 MPa to 1501 ± 15 MPa. A multiphysics model is implemented and compared with experimental results, which reveals the underlying mechanisms of improved sample homogeneity.