High-temperature mechanical properties of laser welds in Co-base superalloy and its improvement by laser surface melting

Summary

The high-power CO₂ laser is extensively used for practical applications such as cutting and welding of metals. Laser welding of superalloys requiring high-quality and high-efficiency welding, however, is seldom employed in heavy industry. Conventional laser welding of metals with filler wire produces the columnar structure which meets at the weld bead centre and leads to deterioration of creep properties. To improve the creep rupture behaviour of joints within this context, this paper describes the development of a laser surface melting technique involving the weld bead surface being remelted by laser. In the experiments described, Haynes 188 Co-base superalloy with a thickness of less than 3 mm is used as the base metal. The spot size of the laser beam used to irradiate the first layer of the weld bead surface is around 3 mm. The depth of the surface melting layer is varied by the travelling speed. The results suggest that both the elongation at fracture and creep rupture life after laser surface melting show a two-fold improvement compared with the as-welded state. Laser surface melting of Co-base superalloy shows that the creep properties can be greatly improved by a rearrangement of the columnar structure boundary.