A fractographical approach to the sintering process in porous ZrB₂-B₄C binary composites

Due to their high temperature stability and hardness, ZrB₂-B₄C composites have drawn attention of researchers in recent years. Although several studies have been conducted on the properties of ZrB₂-B₄C composites at high sintering temperatures (>2200 °C), there is little information about their sintering process and densification at temperatures below 1850 °C, which is industrially more attractive and could result in desirable porosity. In this paper, sintering process and porosity of ZrB₂-B₄C binary composites containing 0 to 100 vol% B₄C (hot pressed at 1800 °C for 30 min under a uniaxial load of 12 MPa) have been studied. The effect of volume fraction of components on sintering process and microstructure has been investigated by Scanning Electron Microscopy of fracture surfaces of samples. The amount and the type of porosity and relative density of samples have also been determined. Results show that the density of samples decreases inversely with the amount of B₄C. Also, the type of porosity changes from closed to open in high B₄C volume fractions. SEM micrographs show that the sintering process is controlled by moss-like ZrO₂ transient phases formed during the heating process.