Joining of C/SiC Materials by Spark Plasma Sintering

Abstract

High density graphite and silicon carbide powder (alpha phase) were used to obtain joints by Spark Plasma Sintering (SPS) technique. The joining of C/SiC was performed both by direct bonding (DB) and with the aid of a ceramic powder mixture (SiC+5%wt.B4C) as intermediary joining material. The joints were performed in vacuum at 1900°C under 30 MPa with a dwell time of 3 minutes. The interface structures of the obtained joints were characterized from the structural and mechanical point of view. XRD analysis of both joints have shown only the presence of crystalline phases of SiC and C while the crystalline phase of B4C was not detected due to its low content (5 wt.%) with a higher degree of amorphization of 9.1% for the junction with interlayer than that of the corresponding junction obtained by DB (5.5%). Interface compositional analyses and SEM images have shown that the process of diffusion bonding was the mechanism both for joining by DB and with a SiC+5wt%B4C interlayer. The Vickers microhardness and Young Modulus values measured by nanoindentation evidenciated a strong increase of HV values (11 – 14 GPa) at interface for the junction with SiC+B4C intermediate layer and, as expected, the highest stiffness (180-197 GPa).