Fracture peculiarities and high-temperature strength of bulk polycrystalline boron

We report the mechanical behavior of a bulk boron ceramic prepared by spark plasma sintering of commercially available beta-boron powder. In order to fabricate polycrystalline boron ceramic, we used a protective tantalum foil reacted with carbon from the graphite die or graphite foil forming a thin layer of TaB2 and TaC covering the boron specimen. This is the first study to show the high-temperature flexural strength, toughness, and Young's moduli of boron up to 1400 degrees C. At 1600 degrees C and above, boron will react with testing environment forming an outer shell. The flexural strength and fracture toughness at room temperature reached an average of 340 MPa and 4.1 MPa m (1/2) , respectively. Despite showing clear signs of plastic deformation on the strain-stress curves, the yield strength of the monolithic boron ceramic exceed 1 GPa at 1200 degrees C. It was determined that fracture at elevated temperatures follows a quasi-transgranular mechanism, where the sub-grains of the boron fracture as plate-like structures. An interpretation for the observed fracture behavior was proposed.

Automated summary

We investigated the mechanical behavior of a bulk boron ceramic prepared by spark plasma sintering of commercially available beta-boron powder. With the addition of a protective tantalum foil, we successfully fabricated polycrystalline boron ceramic and demonstrated its high-temperature flexural strength, toughness, and Young's moduli. The ceramic exhibited promising flexural strength and fracture toughness at room temperature, and yielded an impressive yield strength at elevated temperatures.