1986 Volume 4 Issue 2 Pages 470-476
A CO2 laser has been applied to fusion-welding and surface-melting of sintered zirconia ceramics fully stabilized with CaO, MgO or Y2O3, and chemical compositions and preheating temperature required for preventing cracks have been studied. The results obtained are summarized as follows:
(1) Although macroscopic crack in the base material is prevented at preheating temperatures higher than 1200°C, intergranular microcrack has been developed in the fusion zone in the zirconia ceramics other than CaO-stabilized zirconia containing 1.7%SiO2, 1%MgO and 0.7%Al2O3 as impurities. A low melting point compound of SiO2-MgO-CaO-Al2O3 formed at grain boundary plays an important role to release the shrinkage stress in the fusion zone, producing sound bead.
(2) The weld joint strength is decreased by porosities grown at HAZ at lower welding speeds, and at the bead center at higher welding speeds. As the welding speed becomes faster, both porosities are sup-pressed to grow, increasing weld joint efficiency up to 85-90%. Laser-melted surface layer has shown almost no porosities, providing bending strength and a Weibull modulus which are equal to or somewhat larger than those of the base material.
