Hot pressing, strength, and fracture of calcium hexaboride

Fracture behavior and strength of hot-pressed CaB6 were studied. The modulus of elasticity determined by attaching strain gages to the tensile surface of the bend bars to measure strain, was 55 +- 3 x 106 psi. The results are compared with values for other low density ceramic materials (B4C, SiB6, Be4B, AlB12) in a table. The fracture mode was observed for both modulus of rupture and impact test specimens. Predominantly transgranular fracture, associated with distinct step cleavages is evident. Fracture origins were examined in an effort to understand the strength limiting features in hot-pressed CaB6 specimens. Surface defects, large grain agglomerations, and isolated pore pockets were observed and varied from bar to bar; these were similar to those found in B4C. (U.S.)