Abstract The sealing of sintered ceramics with metal often results in the formation of huge voids that reduce the strength of the final structure. This study therefore investigates the mechanism of void formation during Nb-sealing of an Al2O3 capillary using Nd:YAG laser irradiation. It is found that during the initial stages of cooling the outer surface of the Al2O3 capillary solidifies rapidly, but the Nb wire used as the heat source remains at a higher temperature for longer. This causes any gases emitted from the sealing section at the time of melting to be constrained within the capillary, which eventually leads to the formation of huge voids.
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