Microstructure and Mechanical Properties of High Power CO2 Laser Welded Inconel 625 Nickel Based Alloy

Detailed microstructural analysis, and mechanical properties were investigated for high power CO2 laser welded Inconel 625 nickel based alloy. Weld microstructures showed that a considerable amount of columnar dendrites formed with Nb segregation in the fusion zone and brittle Laves phases were precipitated in the interdendritic regions. The growth direction of the columnar dendrites in the upper and bottom weld was different because of the nonuniform temperature distribution. The tensile properties and stress rupture properties, hardness, impact toughness of the weld joints were evaluated. The results showed that the tensile strength and hardness of fusion zone were near to the base metal but the impact toughness of weld metal was significantly decreased, which resulted from the fact that most of Nb originally dissolved in the base metal were consumed by Laves phases that precipitated in the interdendritic regions of the fusion zone, thereby making less Nb available for the solution strength and increasing the brittleness of weld metal. The tensile fractographs were exhibiting ductile features, but the impact fractographs showed that the brittle intermetallic phases formed in the interdendritic regions.