Joining of Y₂O₃-Doped Aluminum Nitride with High Density Graphite by Spark Plasma Sintering

Abstract

High density graphite disks and aluminum nitride ceramics powders have been utilized to obtain joints by Spark Plasma Sintering technique. The joining was carried out in vacuum, at temperatures of 1700°C, 1800°C and 1900°C, under the pressure of 50 MPa with a constant dwelling time of 5 minutes The AlN ceramics to be joined were also synthesized by ceramic technology standard route by using AlN powders and 2.5 % wt.Y2O3 powders as sintering additive, which were added in order to increase densification rate and by thus, thermal conductivity. The joining of AlN/C was performed both without and with the aid of a ceramic powder composite AlN+Y2O3+C film, as interlayer. Besides the crystalline phases (AlN and C), the Al5Y3O12 compounds with a cubic crystallographic structure were identified by X-ray diffraction. The optical microscopy images revealed that all samples, both without and with film as interlayer, had strong joined areas, without any defects and discontinuities at interfaces. The Vickers microhardness and Young Modulus values measured by nanoindentation have shown that using of the film as intermediary layer was leading to the highest values of mechanical properties (HV = 8 – 23 GPa and E= 227-512 GPa) at the AlN/C joints interfaces.