Solidification features and tensile performance altered by increased welding speed during laser welding GH909 superalloy

In this paper, solidification features and tensile performance under proportionally increased power and speed were systematically studied during laser welding of GH909 alloy. The increase of power density promoted the practical heat adsorption and thus an increasing meting area. Therefore, weld bead geometry was transformed from "Y" to "Hourglass" and again to "Y" under low power and speed (W-1: 1.5 kW and 1.5 m/min) or high types (W-5: 3.5 kW and 3.5 m/min). High power and speed not only promoted dendritic growth in continuous form with progressively developed inter-and intra-grain liquation but also inhibited the equiaxed zone, altered the solidification crack morphology and reduced the eutectic reaction degree. In addition, such condition reduced the epitaxial growth, increased the diversity of growth direction and promoted the growth concentration with aggravated grain size inhomogeneity near to fusion line while an original texture of 100//TD was also changed to a deflected and diverse fashion with apparent grain coarsening in weld center. The above occurrences were attributed to the reduced duration time of gamma forming and gamma/Laves eutectic reactions, as well as temperature gradient variations near FL and weld center. W-1 presented a higher strength and elongation rate due to the inhabitation of the coarse grains, high slipping tendency and strip-like cracks.