Sintering and Mechanical Properties of ZrB sub(2)-TaSi sub(2) and HfB sub(2)-TaSi sub(2) Ceramic Composites

• Published in: Journal of the American Ceramic Society Vol. 91; no. 10; pp. 3285 - 3291
• Main Authors: Sciti, Diletta, Silvestroni, Laura, Celotti, Giancarlo, Melandri, Cesare, Guicciardi, Stefano
• Format: Journal Article
• Language: English
• Published: 01.10.2008
• Subjects: Borides; Ceramics; Flexural strength; Hot pressing; Modulus of rupture in bending; Sintering; Solid solutions; Strength
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1551-2916.2008.02593.x

Fully dense fine-grained ZrB sub(2)- and HfB sub(2)-based composites contaning 15 vol% TaSi sub(2) were produced by hot pressing at 1850-1900C. Gas formation and mass loss, which occurred during sintering in both systems, were in agreement with thermodynamic predictions. In both composites, the presence of a solid solution formed by the diffusion of tantalum into the boride matrix was observed. The HfB sub(2)-based composite was harder (22 GPa), stiffer (528 GPa), and tougher (4.1M Pa.m super(1-2)) than the ZrB sub(2)-based composite. Although the room-temperature flexural strength of the ZrB sub(2)-based composite (830 MPa) was higher than that of the HfB sub(2)-based composite (700 MPa), the opposite was true at 1200 and 1500C. Contrary to the significant strength decrease observed for the ZrB sub(2)-based materials at elevated temperature, the HfB sub(2) composite retained 686% of its room temperature strength up to 1500C (6600 MPa).