The influence of the spark plasma sintering (SPS) heating rate on densification, microstructure and strength of ZrB2-20 vol.% SiC composites with or without 5 vol. A, Yb2O3 addition was assessed. A low heating rate promoted densification, induced grain growth and slightly increased the strength in the Yb2O3-free ceramics, whereas the low heating rate inhibited the densification, maintained the grain size and greatly decreased the strength in the Yb2O3-doped composites. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.