Development of B4C-HfB2 composites by reaction hot pressing

This paper reports on the development of HfB2 reinforced B4C composite prepared through reaction hot pressing of B4C and HfO2. These composites were characterized for phase composition, microstructure, mechanical and physical properties. Full dense composites were obtained by hot pressing at 1900 degrees C and a pressure of 40 MPa. HfB2 phase was identified as a reaction product in the composites by XRD analysis. Hardness of all the composites was measured to be in the range of 28-35 GPa. High elastic modulus (525 GPa) and shear modulus (196 GPa) were measured for composite corresponding to 10 wt.% HfO2. Fractography of the composites indicates transgranular mode of fracture. Fracture toughness of the composites was in the range of 4-7 MPa.m(1/2) which is higher than that of monolithic B4C (2.43 MPa.m(1/2)). Microstructural observation of crack propagation patterns indicates the major toughening mechanism as crack deflection, crack arrest and crack bridging. (C) 2012 Elsevier Ltd. All rights reserved.