Clarifying the effect of sintering conditions on the microstructure and mechanical properties of β-tricalcium phosphate

The effect of the sintering conditions (temperature and time) on the microstructure (density and grain size) and mechanical properties (hardness, elastic modulus, and strength) of beta-tricalcium phosphate (beta-TCP) bioceramics fabricated from Ca-deficient commercial powders is analyzed. Contrary to current general opinion, it is demonstrated that the optimal sintering temperature to maximize the mechanical performance of this beta-TCP material is not necessarily below the beta <-> alpha transformation temperature (1125 degrees C). In particular, optimal performance was achieved in samples sintered at 1200 degrees C for 3 h, since it was not until higher temperatures or longer sintering times that microcracking develops and mechanical properties are degraded. It is argued that the residual stresses developed during this reversible transformation do not lead to microcrack propagation until sufficiently large starting flaws develop in the microstructure as a consequence of grain growth. Implications of these findings for the processing routes to improve sintering of this important bioceramic are discussed. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.