Tetiana Prikhna

Abstract:

Lightweight shockproof ceramics based on aluminum dodecaboride (AlB12) hold great potential for a wide range of applications, such as protective armor or constructional ceramics for nuclear power plants. Interest in higher aluminum borides and aluminum dodecaboride in particular exists for a long time. However, these materials have not found widespread use because of the lack of industrial and semi-industrial technologies for their powder production. At present, aluminum dodecaboride powders are produced in small amounts in laboratories. In this regard, the processes of sintering of aluminum borides and properties of the consolidated materials on their basis have not been sufficiently studied and practically are not described in the literature. Higher aluminum borides were studied from the point of view of their use as solid fuel, abrasives, explosives and additives to the boron-carbide-based materials. The results of the complex investigation of AlB12-based ceramics sintered from submicron -AlB12 powder at varying pressures and temperatures will be discussed. The effect of C and TiC additions on the structure and mechanical properties of the resultant products is also investigated. Materials sintered from -AlB12 powder at 30 MPa, 2080-1950oC were found to contain 94-98% of -AlB12 ( = 2.53-2.58 g/cm3) and have the following mechanical properties: hardness, HV (49 N) = 24.1 GPa; fracture toughness, K1c (49 N) = 4.9 MPa·m0.5; bending strength, Rbs = 336 MPa; and compressive strength, Rcs = 378 MPa. The sintering pressure of 2 GPa resulted in the formation of dense -AlB12 at 1200-1400oC with much lower hardness, HV (49 N) = 15.1-15.9 GPa, and higher fracture toughness, K1c (49 N) = 5.6  1.3 MPa·m0.5. Addition of 17% C to the -AlB12 powder changed the phase composition of the material sintered at 30 MPa, 1950 °C to 86% AlB12C2 with  = 2.67 g/cm3 and lead to the increase of K1c (49 N) to 5.9 MPa·m0,5 and Rcs to 423 MPa. The material sintered from -AlB12 powder at 30 MPa and 1950 °C with 20 % TiC addition contained 74% AlB12C2, 22% TiB2, 4% Al2O3, had high mechanical characteristics, HV (49N) = 28.9 GPa, K1c (49 N) = 5.2 MPa·m0.5, Rbs = 633 MPa and Rcs = 640 MPa, but its density increased to =3.2 g/cm3. Addition of 12% TiC allowed formation of the material with  = 2.74 g/cm3, HV (49N) = 19.4 GPa, K1c (49 N) = 7 MPa·m0.5, and phase composition of 49% AlB12C2, 34% -AlB12, 14% TiB2. The SEM study revealed even more complicated structures, possibly due to the formation of solid solutions.