Modelling of the enhanced densification in ultra-fast high temperature sintering: impact of porosity shape
WANG S. 1, MAKSYMENKO A. 2, DENG Y. 1,3, KALETSCH A. 1,3, OLEVSKY E. 2, BROECKMANN C. 1,3
1 Institute of Applied Powder Metallurgy and Ceramics at RWTH Aachen e.?V. (IAPK), RWTH Aachen University, Aachen, Germany; 2 Department of Mechanical Engineering, San Diego State University, San Diego, United States; 3 Institute for Materials Applications in Mechanical Engineering (IWM), RWTH Aachen University, Aachen, Germany
Ultrafast High-temperature Sintering (UHS) is a novel sintering technique which allows densification of ceramics in a few tens of seconds. The powder compact is placed within a carbon strip heated by Joule effect at a heating rate up to 104 K/min. One major consolidation enhancing factor for UHS is the ultra-high heating rate, which can suppress surface diffusion processes that do not contribute to densification. A limited surface diffusion could increase the driving force of sintering by delaying the pore spheroidization process and remaining the highly reactive particle contact microstructures with star-like porosity shape. In this study, the impact of porosity shape on the sintering related parameters, such as stress intensification factor and viscosity modulus, was analyzed. The Skorohod-Olevsky Viscous Sintering (SOVS) constitutive model was modified with the consideration of pore structure by introducing an additional parameter of dihedral angle in the expression of the sintering stress and viscosity modulus. The ability of the model to predict the densification for both conventional sintering and UHS using finite element methods (FEM) was confirmed by the experimental results of strontium titanate (SrTiO3). This evidenced that the high heating rate speeds up the densification during UHS by maintaining a porous skeleton microstructure with a pronounced delay in surface diffusion.