High-Cycle Fatigue Performance of Laser Powder Bed Fusion Ti-6Al-4V Under As-Built and Hot Isostatic Pressing Conditions

This study investigates high-cycle fatigue life of laser powder bed fusion Ti-6Al-4V under as-built versus post-process hot isostatic pressing conditions within the context of additive manufacturing and metallic fatigue mechanics, an area of growing scientific importance given its implications for qualification standards for additively manufactured structural aerospace components. Using staircase fatigue testing at R = -1 to determine S-N curves and fatigue limits at 10 million cycles, we examine subsurface porosity and lack-of-fusion defects acting as fatigue crack initiation sites in as-built specimens in 90 fatigue specimens (45 as-built, 45 HIP-treated) across three build orientations (horizontal, vertical, 45-degree) drawn from controlled laboratory fatigue test frame environment at ambient temperature. Results indicate that HIP treatment increases the 10-million-cycle fatigue limit by 38.2% in horizontally built specimens (634 MPa vs. 459 MPa) and eliminates orientation-dependent fatigue scatter (p < 0.001), with 38.2% fatigue limit improvement with HIP as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to additive manufacturing and metallic fatigue mechanics and carry actionable implications for the design of programs and policies targeting qualification standards for additively manufactured structural aerospace components.