Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2010, Article ID 835018, 11 pages doi:10.1155/2010/835018 Research Article Sintering Behavior, Microstructure, and Mechanical Properties: A Comparison among Pressureless Sintered Ultra-Refractory Carbides Laura Silvestroni and Diletta Sciti CNR-ISTEC, Institute of Science and Technology for Ceramics, Via Granarolo 64, I-48018 Faenza, Italy Correspondence should be addressed to Laura Silvestroni,
[email protected] Received 12 July 2010; Accepted 10 October 2010 Academic Editor: Paul Munroe Copyright © 2010 L. Silvestroni and D. Sciti. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Nearly fully dense carbides of zirconium, hafnium, and tantalum were obtained by pressureless sintering at 1950 ◦C with the addition of 5–20 vol% of MoSi2. Increasing the amount of sintering aid, the final density increased too, thanks to the formation of small amounts of liquid phase constituted by M-Mo-Si-O-C, where M is either Zr, Hf, or Ta. The matrices of the composites obtained with the standard procedure showed faceted squared grains; when an ultrasonication step was introduced in the powder treatment, the grains were more rounded and no exaggerated grains growth occurred. Other secondary phases observed in the microstructure were SiC and mixed silicides of the transition metals. Among the three carbides prepared by pressurless sintering, TaC-based composites had the highest mechanical properties at room temperature (strength 590 MPa, Young’s modulus 480 GPa, toughness 3.8 MPa·m1/2).