Comparative study of dot-ring and Gaussian beams on epitaxial grain growth and crack suppression of DD6 superalloy fabricated by laser powder bed fusion

Abstract

The energy distribution profile of the laser beam plays a crucial role in determining melt pool stability and the mechanisms of defect formation during laser powder bed fusion (LPBF) process. In this study, DD6 nickel-based superalloy specimens were fabricated using Gaussian and dot-ring beam(sometimes referred to as a flat-top laser) to investigate the influence of laser energy distribution on microstructural evolution and mechanical properties.The results reveal that the dot-ring beam with a uniform energy profile significantly increases the melt pool's width-to-depth ratio and promotes melt pool stability. Samples produced using the dot-ring beam exhibited a pronounced [001] crystallographic texture, with an average grain misorientation angle of 13.6°. Due to the reduced presence of defects and high-angle grain boundaries (HAGBs), these samples achieved the highest ultimate tensile strength (UTS) of 1205 MPa and an elongation at break of 15.2 %. Compared to samples fabricated using the Gaussian beam, this represents an improvement of 20.1 % in UTS and 46.15 % in elongation. The tensile fracture surfaces displayed a mixed brittle–ductile fracture mode.Moreover, the adoption of the dot-ring beam significantly expanded the process window. High-density parts could be achieved as long as the volumetric energy density (VED) met the minimum threshold. This study provides theoretical guidance and practical reference for the LPBF processing of high-performance nickel-based superalloys.