Effect of laser intensity profile on the microstructure and texture of Inconel 718 superalloy fabricated by direct energy deposition

Abstract

Epitaxial growth of dendrites often results in a strong texture, which is a common phenomenon in a laser additive manufacturing process. In this study, pulsed lasers with flat-top and Gaussian intensity profiles were used to modulate the molten pool morphology and the solidification texture with a unidirectional scanning strategy. The melt pool is planar for the flat-top mode and it turns arc-shaped for the Gaussian mode. Long columnar grains are uniformly distributed and a strong fiber texture with a weak cube texture is obtained for the flat-top mode sample due to a uniform heat flux through many deposition layers. In contrast, large grains and fine grains are alternately arranged for Gaussian mode sample. The large grains exhibit a strong rotated cubic texture with a V-pattern in the overlapping area of the melt pool due to side-branching from the curved melt pool boundary; while the fine grains exhibit a weak fiber texture in the center of melt pool with a less restriction of the other two crystallographic axes perpendicular to the build direction. After heat treatment, the intensity of the textures of both samples is reduced. More recrystallized grains with twin boundaries are found under Gaussian mode due to the accumulated residual strain. This work manifests a promising method for texture customization by manipulating the heat flux strategy for laser additive manufacturing.