Lightweight Alumina-B4C composites for structural and functional applications.

Al2O3-B4C composites with 0, 5, 10, 15, and 50 vol% B4C additions were consolidated by hot pressing (HP) and pressureless sintering (PLS). The influence of the B4C additive on the densification behavior, microstructure and mechanical properties of the composites was investigated. Detailed SEM-EDS and XRD studies highlighted differences in microstructures and secondary phase formations. The evolution of the Gibbs free energy at different temperatures and the equilibrium phases were calculated by means of thermodynamic simulations. These analyses showed that formation of Al-B-O gaseous phases was affected by atmospheric conditions (vacuum or Ar flux). Addition of 50 vol% of B4C promoted an increase of hardness and toughness (?24 GPa and ?5.85 MPam1/2) and a substantial decrease of weight (?18%) compared to monolithic alumina, which could be of interest for armor and other structural applications. Besides, functional applications were considered. The addition of B4C caused a marked change of colour and increase of solar absorbance. The optical properties of these composites were investigated in view of possible applications as solar receivers in concentrating solar power system.