The effect of Fe addition on processing and mechanical properties of reaction infiltrated boron carbide-based composites

Dense metal-ceramic composites based on boron carbide were fabricated using boron carbide and Fe powders as starting materials. The addition of 3.5– 5.5 vol% of Fe leads to enhanced sintering due to the formation of a liquid phase at high temperature. Preforms, with about 20 vol% porosity were obtained by sintering at 2,050 C even from an initial boron carbide powder with very low sinterability. Successful infiltration of the preforms was carried out under vacuum (10–4 torr) at 1,480 C. The infiltrated composite consists of four phases: B12(C, Si, B)3, SiC, FeSi2 and residual Si. The decrease of residual Si is due to formation of the FeSi2 phase and leads to improved mechanical properties of the composites. The hardness value, the Young modulus and the bending strength of the composites fabricated form a powder mixture containing 3.5 vol% Fe are 2,400 HV, 410 GPa and 390 MPa, while these values for the composites prepared form iron free B4C powder are 1,900 HV, 320 GPa and 300 MPa, respectively. The specific density of the composite was about 2.75 g/cm3. The experimental results regarding the sintering behavior and chemical interaction between B4C and Fe are well accounted for by a thermodynamic analysis of the Fe–B–C system.