Enhancing mechanical properties and isotropy in ultrasonic assisted powder bed fusion of metals using a laser beam (PBF-LB/M) via Dual Exposure

• A novel dual-exposure strategy enabling effective ultrasonic assistance in PBF-LB/M without disturbing the powder bed. • Reduction of up to 55 % in tensile-strength anisotropy and 46 % reduction in yield-strength anisotropy via UA processing. • EBSD-confirmed grain refinement and increased nucleation site density, with characterization of secondary dendrite-arm formation in ultrasonic assisted PBF-LB/M. • Identification of a 280 % increase in surface roughness due to ultrasonic assisted PBF-LB/M. Parts produced via powder bed fusion of metal using a laser beam process often exhibit mechanical anisotropy due to the directional solidification, complicating part design. This study explores the use of ultrasonic-assistance to reduce anisotropy by promoting microstructural homogenization through increased nucleation. Specimens were fabricated using a dual exposure strategy, to avoid the challenges that arise with the in-situ ultrasonic excitation of a powder bed. Furthermore, a comprehensive microstructural as well as mechanical analysis was carried out. Microstructural analysis revealed increased grain orientation variation in ultrasonically treated specimens. Mechanical testing showed improved tensile and yield strength and reduced anisotropy, with tensile and yield strength anisotropy decreasing by 55.4 % and 46.1 %, respectively. Despite increased surface roughness, ultrasonic treatment reduced anisotropy in ductility-related properties, highlighting its potential to improve the performance of additively manufactured parts by reducing anisotropy and simultaneously enhancing mechanical properties.