High Temperature Mechanical Properties in Laser Welds of Co-base superalloy and its Improvement by Laser Surface Melting

The high power CO2 laser utilizes widely for practical applications such as cutting and welding of metals because of its large scale of output power. However laser welding of superalloys which required a high quality and a high efficient welding, is rarely applied in practical use in the field of heavy industry. An ordinary laser welding of metals with filler wire produces the columnar structure which meets at the center of weld bead, so this leads to decrease of creep properties. At this point of view, we have developed to improve creep rupture behavior of joints by laser melting the surface of weld bead again. In this experiment, Co-base superalloy of less than 3 mm thickness was used as a base metal. The spot size of laser beam to irradiate on the first laser weld bead surface was approximately 3 mm. The depth of this surface melting layer was changed by traveling speed within this experiment. As a result, it was found that both its elongation and creep rupture life time after laser melted were improved to twice compared with as welded. The laser surface melting on laser welds of Co-base superalloy shows that the creep properties can be greatly improved by re-distribution of the boundary of the columnar structure.