Plasma arc welding of ZrB2–20 vol% ZrC ceramics

Zirconium diboride ceramics containing 20 vol% zirconium carbide were preheated to 1450 °C and plasma arc welded to produce continuous joints. Arc welding was completed using a current of 198 A, plasma flow rate of 0.75 l/min, and welding speed of ∼8 cm/min. Two fusion zones, having penetration depths of 4.4 and 2.3 mm, resulted in different microstructures. One fusion zone contained ZrB2 crystals, up to ∼1 mm in length, and a ZrB2–ZrC eutectic. The second fusion zone revealed ZrB2 and ZrC, along with C that was attributed to diffusion from the graphite support used during welding. ZrB2 and ZrC grains in the latter fusion zone were asymmetric, having an average maximum Feret diameter of 52.4 ± 53.2 μm and 10.8 ± 8.1 μm, respectively. Hardness, used to identify a heat affected zone for both weldments, increased from 12 GPa at the fusion zone boundary, to the hardness of the parent material, 15.2 ± 0.1 GPa.