Spark plasma sintering and high-temperature strength of B6O-TaB2 ceramics

Tantalum diboride - boron suboxide ceramic composites were densified by spark plasma sintering at 1900 C-omicron. Strength and fracture toughness of these bulk composites at room temperature were 490 MPa and 4 MPa m(1/2), respectively. Flexural strength of B6O-TaB2 ceramics increased up to 800 C-omicron and remained unchanged up to 1600 C-omicron. At 1800 C-omicron a rapid decrease in strength down to 300 MPa was observed and was accompanied by change in fracture mechanisms suggestive of decomposition of boron suboxide grains. Fracture toughness of B6O-TaB2 composites showed a minimum at 800 C-omicron, suggestive a relaxation of thermal stresses generated from the mismatch in coefficients of thermal expansion. Flexural strength at elevated temperatures for bulk TaB2 reference sample was also investigated. Results suggest that formation of composite provides additional strengthening/toughening as in all cases flexural strength and fracture toughness of the B6O-TaB2 ceramic composite was higher than that reported for B6O monoliths. (C) 2017 Elsevier Ltd. All rights reserved.