Spark plasma sintering of a commercially available granulated zirconia powder: Comparison with hot-pressing Guillaume Bernard-Granger a, * , Ahmed Addad b , Gilbert Fantozzi c , Guillaume Bonnefont c , Christian Guizard a , Dorothe ´e Vernat a a Laboratoire de Synthe `se et Fonctionnalisation des Ce ´ramiques, UMR 3080 CNRS/Saint-Gobain, Saint-Gobain CREE, 84306 Cavaillon Cedex, France b Laboratoire de Structure et Proprie ´te ´s de l’Etat Solide, UMR 8008 CNRS, Universite ´ des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq Cedex, France c Laboratoire MATEIS, UMR 5510 CNRS, Institut National des Sciences Applique ´es de Lyon, 69621 Villeurbanne Cedex, France Received 10 November 2009; received in revised form 5 January 2010; accepted 7 February 2010 Available online 11 March 2010 Abstract A commercially available granulated TZ3Y powder has been sintered by hot-pressing (HP). The “grain size/relative density” relation- ship, referred to here as the “sintering path”, has been established for a constant value of the heating rate (25 °C min 1 ) and a constant value of the macroscopic applied pressure (100 MPa). It has then been compared to that obtained previously on the same powder but sintered by spark plasma sintering (SPS, heating rate of 50 °C min 1 , same applied macroscopic pressure). By coupling the analysis of a sintering law (derived from creep rate equations) and comparative observations of sintered samples using transmission electron micros- copy, a hypothesis about the densification mechanism(s) involved in SPS and HP has been proposed. Slight differences in the densifica- tion mechanisms lead to scars in the microstructure that explain the higher total ionic conductivity measured, in the temperature range 300–550 °C, when SPS is used for sintering. Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Ceramics; Sintering; Transmission electron microscopy (TEM); Electrical resistivity/conductivity 1. Introduction Spark plasma sintering (SPS) of a commercially avail- able TZ3Y granulated zirconia powder has been studied and reported in two previous companion papers [1,2]. The microstructure of the sintered samples has been investigated using transmission electron microscopy (TEM) coupled with energy-dispersive spectroscopy (EDS) nano-analyses and, in all cases, was found to be compatible with the densification mechanisms invoked [1,2]: grain boundary sliding was accommodated by an in-series (interface-reaction/lattice diffusion of the Zr 4+ and/or Y 3+ cations) mechanism controlled by the inter- face-reaction step for the lower temperatures or the lower effective compaction stresses when the temperature is higher. It implicitly signifies that grain boundaries are not perfect sources/sinks of vacancies; a dislocation-climb-con- trolled mechanism assisted by grain boundary sliding was active when the samples were sintered at the higher temper- atures or at high effective compaction stresses for lower temperatures. The fact that Moire ´ patterns were observed confirms that grain boundary sliding controls densification. Such special interference figures at grain boundaries are related to the overlapping of two elemental grains having a similar crystallographic orientation. But to overlap, the grains have first to slide on each other and rotate to achieve a suitable orientation. Emission of bulk dislocations is then a consequence of stress relaxation accumulated at grain boundaries during grain boundary sliding. The electrical conductivity of some samples sintered by SPS has been measured, using impedance spectroscopy in 1359-6454/$36.00 Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2010.02.013 * Corresponding author. E-mail address: guillaume.bernard-granger@saint-gobain.com (G. Bernard-Granger). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 58 (2010) 3390–3399