Ultrasonic surface post-processing of hot isostatic pressed and heat treated superalloy parts manufactured by laser powder bed fusion

Abstract

• IN 718 alloy parts were fabricated by laser powder bed fusion (L-PBF). • Hot isostatic pressing (HIP) was applied to enhance material density. • Homogenization and aging were applied to provide the required structure and grain size. • Surface improvement was implemented by ultrasonic impact treatment (UIT). • Surface texture, roughness, waviness, structure, and residual stress were studied. Inconel 718 alloy parts were fabricated by the laser powder bed fusion (L-PBF) technique using a multidirectional stripe scanning strategy. Subsequently, the L-PBF-built parts were hot isostatic pressed (HIP), homogenized, and aged. Ultrasonic surface mechanical treatment was applied to modify the surface texture and microstructural layer of the L-PBF-built and heat-treated Inconel 718 alloy parts. Ultrasonic impact treatment (UIT) was implemented using a forcedly rotated multi-pin impact head. The surface texture, roughness, waviness, porosity, microstructure, phase composition, hardness, and residual stresses of the L-PBF-built and thermo-mechanical post-processed specimens were studied and compared. The results revealed that the UIT post-processing leads to work hardening, induces compressive residual stresses, and ∼20% increase in the surface microhardness in the near-surface layer of the heat-treated L-PBF-built 718 alloy parts. The surface roughness and waviness were significantly reduced after UIT, providing a flattened surface microrelief formation.