Relationship between microstructure and experimental conditions 23-27 june 2013, Limoges, France Relationship between microstructure and experimental conditions in the flash sintering of YSZ ceramics Marlu César STEIL, Daniel MARINHA Laboratoire d’Electrochimie et de Physico-chimie des Matériaux et des Interfaces – UMR 5279 Université de Grenoble BP.75. 38402 Saint Martin d’Hères Cedex - FRANCE Purpose/Objectives We concentrated our attention on the microstructures obtained by varying the flash-sintering parameters: Flash sintering Two-electrode-experiments using AC electrical fields 1,2 furnace temperature (initial temperature T0); initial power spike the steady state current density, the flash time   V(volt) i(A) Porous Sample dense t(seconds!!) flash-sintering First set of results : initial temperature of 900°C was selected and typical flash conditions were applied, varying the current density and flash time over the 7-50 s range. Second part of this work is focused on the initial period, limited to 1s, that we will call the hyper-flash. Flash-sintering on the conventional 8 mol% Y2O3 doped ZrO2 Experimental -----Sample processing and characterization----- Samples: pellets (8 mm in diameter, 3 mm thick) uniaxial pressing and IP (250 MPa). Green relative densities: 50,O ± 0,5% TD (Theoretical Density). Powder : 8 mol.% yttria stabilised zirconia (Tosoh TZ-8Y) Post-sintering characterizations : Densities: determined geometrically and by the Archimede method; Microstructures : FEG-SEM on fracture surfaces Electrical characterization by Impedance Spectroscopy -----Flash-sintering equipment and procedures----- Sample is heated in the experimental furnace (temperature ramp: 10°/mn) to the the initial sample temperature (900°C) and then electric signals are applied (AC signals, 1000Hz, to avoid electrolysis) To avoid any electrical breakdown, we used a current limitation (Pacific Smart Source 115ASX AC power generator) flashes were performed under constant current densities and not under constant electric fields The current increases very rapidly and is limited to the selected value (from 5 to 20 A.cm-2) The flash was triggered by applying an appropriate electric field Input Parameters: Furnace Temperature T0; Current max i; Initial voltage V0; Flash time Dt Results Grain size ~ ; Density time 1 Conventional flash sintering furnace temperature : 900°C;Initial elect. field E= 170Vcm-1 10A/cm2 – 7s 10A/cm2 – 30s 10A/cm2 – 45s - t 14A/cm2 Dt = 30s Initial power : 2100 W.cm-3 i (A/cm2) t (s) Relative density (%TD) Grain size (µm) Geom. Arch. 10 7 81 -- 0.5 30 89 87 0.3 45 96 98 0.5 - 1 14 92 94 93 1 - 2 97 1-2 20 3 2-3 2 -3 Current 14A/cm2 – 7s 14A/cm2 – 30s Conventional sintering 1350°C/1h Grain size Density 20A/cm2 – 7s 20A/cm2 – 14s Impedance measurements Conductivity of flashed samples is equivalent to conventional YSZ 2Hyper flash sintering (t1s) furnace temperature : 900°C E=150Vcm-1 - 10A/cm2 Initial power : 1500W.cm-3 E=300Vcm-1 - 10A/cm2 Initial power : 3000W.cm-3 Electrical Field 80%TD Grain size and density ~ 78%TD Conclusions AC flash sintering: versatile investigation tool for the sintering studies. Appropriate selection of experimental parameters lead to a wide variety of microstructures and different states of densification The microstructures do not reveal any specific feature associated with the flash-sintering process. The quality of the sintered samples was confirmed by impedance spectroscopy Major part of densification (up to 80%) occurs within a short time interval of about 1s with a minor grain growth Acknowledgements This work was partially funded by the French National Research Agency The authors thank Dr. F Roussel Dherbey and Dr. F. Charlot (CMTC, INP Grenoble) for SEM observations. A. Cordier , M. Kleitz, M. C. Steil, Journal of the European Ceramic Society, 32 (2012) 473–1479 M. C. Steil, D. Marinha, Y. Aman, J. R.C. Gomes, M. Kleitz, Journal of the European Ceramic Society 33 (2013) 2093–2101