Suzuya Yamada

High strength B4C–TiB2 composites fabricated by reaction hot-pressing

Abstract B 4 C based composites with 20 mol% TiB 2 were fabricated by reaction hot-pressing of four different submicron size B 4 C powders with the addition of nanometer size TiO 2 and C powders at 2000xa0°C, and their mechanical properties were examined. A B 4 C–TiB 2 composite with both high strength of 866 MPa and modest fracture toughness of 3.2 MPa m 1/2 could be obtained using B 4 C powder with a mean particle size of 0.50 μm and total metal impurity 0.3–0.5 wt.% (Al + Fe). It seems that this extremely high strength is attributed to the fine-grained B 4 C microstructure, uniform dispersion of TiB 2 particles and improvement of fracture toughness.

B4C−CrB2 composites with improved mechanical properties

Abstract B4C based ceramic composites with 0−25 mol% CrB2 were fabricated by hot-pressing at 1900xa0°C, and their mechanical properties were examined. The B4C−CrB2 composites with both high strength of 630 MPa and modest fracture toughness of 3.5 MPa m1/2 could be obtained by the addition of 20 mol% CrB2. It seems that improvement in fracture toughness is due to the formation of microcracks and deflection of propagating cracks caused by the thermal expansion mismatch between CrB2 and B4C.

Mechanical and electrical properties of B4C–CrB2 ceramics fabricated by liquid phase sintering

Abstract B 4 C based ceramic composites with additions of CrB 2 up to 25 mol% were fabricated by hot pressing at 2050xa0°C with a low applied load of 5 MPa. The CrB 2 addition enhanced the densification of B 4 C due to the formation of CrB 2 –B 4 C eutectic liquid. Both a high strength of 684 MPa and a modest fracture toughness of 3.2 MPa m 1/2 were obtained for the B 4 C– 22.5 mol% CrB 2 specimen. Furthermore, the electrical conductivity was increased remarkably for the specimens with more than 15 mol% CrB 2 , which was attributed to the formation of three-dimensional network of the electrically conductive CrB 2 phase.