Surface densification of porous ZrB2–39 mol.% SiC ceramic composites by a laser process

40% porous composites ZrB2–39 mol.% SiC were irradiated under a mobile laser beam, with a low power of 90 W, in a protective atmosphere of flowing argon. Quasi-full densification of the surface zone was obtained, with thicknesses of more than 20 μm. Temperature reached ca. 2500 °C and a fusible phase rich in SiC appeared, which partially dissolved the ZrB2, favouring its sintering. The liquid phase filled the porosity present between the ZrB2 grains, and migrated towards the surface and the bulk of the samples. After cooling, the liquid phase demixed, according to the ZrB2–SiC phase diagram, and the phases ZrB2 and SiC interweaved in a eutectic-like solid phase, co-existing with granular zones mainly composed of ZrB2. Only few cracks were observed. Traces of free carbon were found at the surface, while oxygen never penetrated inside the samples, despite the presence of traces of this element in the surrounding atmosphere. These two last observations were explained by a thermodynamic study. The pellets so obtained could find applications in the fields of aerospace and of low-temperature protonic ceramic fuel cells.