Additive manufacturing has gained prominence in aerospace engineering, particularly for fabricating complex and high-performance components using Laser Powder Bed Fusion (L-PBF). However, the inherent surface roughness in as-built L-PBF parts poses significant challenges for ultrasonic testing (UT), leading to signal scattering, noise elevation, and reduced flaw visibility.

This study investigates the impact of surface roughness on ultrasonic testing (UT) performance in L-PBF manufactured in 718 components. The research systematically evaluates how different surface conditions—as-built, grit blasted, etched, and machined affect ultrasonic signal response, apparent attenuation, and defect detection reliability. Two specimen configurations were employed: the first set with different surface conditions for evaluating surface roughness effects, and the second set with embedded artificial defects for assessing defect detectability using two probe configurations. Ultrasonic inspections were conducted using both a conventional focused probe and a phased array annular probe under immersion pulse-echo configurations.

Results demonstrate that surface roughness is the primary factor influencing UT performance. Machining reduced apparent attenuation from 0.112 dB/mm (as-built) to 0.0718 dB/mm, improving energy transmission and echo clarity. Surface finishing enhanced defect detectability: the conventional probe reached 0.8 mm thresholds on machined surfaces, while the phased array probe detected flaws down to 0.4 mm post-machining and 0.6 mm in as-built. Water path variation tests further highlighted the importance of proper focal zone alignment for maintaining image clarity and flaw visibility.This research establishes that surface roughness is the most critical factor limiting ultrasonic inspection performance in L-PBF components. Machining provides the most significant improvement, while phased array annular probes offer superior detection capabilities. The findings contribute to optimized ultrasonic testing strategies for additively manufactured aerospace components, ensuring reliable flaw detection across varying surface conditions in safety-critical applications.