Microstructural analyses of B4C-CeO2 and B4C-La2O3 ceramics

Effects of additions of CeO2 and La2O3 on microstructure and mechanical properties of B4C fabricated under and without hot press have been investigated. Vickers hardness and fracture strength are increased by hot press due to the reduction of porosity because the sintering rate is enhanced. Hardness is increased by the reduction of porosity because crack probably occurs when the hardness is measured due to pore as an initiation point of crack. Hardness increases with increasing additions of CeO2 and La2O3 because porosity decreases due to the formation of CeB6 and LaB6 on the grain boundary of B4C, respectively. The borides are formed through reaction between solid phases, which might induce coherent boundary between boride and B4C. Such coherency also contributes to strengthening the grain boundary of B4C. The addition of CeO2 enhances the sintering rate more than that of La2O3, resulting in higher hardness of B4C-CeO2 than that of B4C-La2O3.