Influence of Voids on Fatigue Life of 3D Printed Titanium Alloy Specimens

Significance of the Topic

Fatigue performance of additively manufactured Ti6Al4V components is critical for aerospace, biomedical implants and other load-bearing applications.
The presence of internal voids inherent to Powder Bed Fusion processes can drastically reduce part reliability and service life.
Understanding the relationship between defect characteristics and fatigue life informs quality control and process optimization in additive manufacturing.

Objectives and Study Overview

This study aimed to correlate internal voids with fatigue behavior of 3D-printed titanium specimens.
Three analytical techniques were combined:

• Microfocus X-ray computed tomography (CT) to visualize and quantify internal pores.
• Ultrasonic fatigue testing to rapidly assess cycles to failure under high-frequency loading.
• Electron probe microanalysis (EPMA) for fracture surface examination and crack initiation localization.

Six specimens produced by electron beam Powder Bed Fusion and machined to standardized geometry were evaluated.

Methodology and Instrumentation

A central 8 mm long volume of each specimen was scanned by inspeXio SMX-225CT FPD HR Plus using VGSTUDIO MAX software for void segmentation and sizing.
Fatigue tests employed the USF-2000A ultrasonic testing machine at 20 kHz with air cooling and temperature monitoring below 30 °C according to JWES WES 1112:2022.
Fracture surfaces and cross sections were analyzed with EPMA™-8050G to pinpoint crack origins relative to pore locations.

Main Results and Discussion

CT analysis revealed reproducible void distributions with volumes up to 1×10⁻³ mm³, exhibiting spherical and crack-like morphologies both internally and at the surface.
Fatigue life divided into two regimes:

• High-cycle fatigue (10⁵–10⁶ cycles) for specimens with surface-connected pores at 350 MPa or 300 MPa.
• Very-high-cycle fatigue (10⁸–10⁹ cycles) when voids were fully internal.

No direct correlation between applied stress amplitude and lifetime was observed; instead, pore location controlled the failure regime.
EPMA confirmed that surface voids initiated cracks under lower cycle counts, whereas internal voids drove failures at very high cycle numbers.

Benefits and Practical Applications

The integrated CT-ultrasonic-EPMA workflow enables non-destructive defect characterization, rapid fatigue screening and precise crack origin mapping.
This approach supports additive manufacturing process validation, enhances component reliability and accelerates research on void mitigation strategies.

Future Trends and Potential Applications

Further work may investigate the impact of void size distribution, morphology and clustering on fatigue behavior.
Integration of in-situ process monitoring, machine learning-based defect prediction and extension to other alloy systems will broaden the methodology’s applicability.
Advances in CT resolution and high-throughput ultrasonic testing promise deeper insights into very-high-cycle fatigue mechanisms.

Conclusion

The study demonstrates that void location predominantly governs fatigue life in 3D-printed Ti6Al4V specimens.
A combined analytical platform of CT scanning, ultrasonic fatigue testing and EPMA fracture analysis offers a powerful toolset for improving additive manufacturing quality and reliability.

Reference

• P. Li et al. Critical assessment of the fatigue performance of additively manufactured Ti6Al4V and perspective for future research. International Journal of Fatigue, 85, 130–143 (2016).
• J. Günther et al. Fatigue life of additively manufactured Ti–6Al–4V in the very high cycle fatigue regime. International Journal of Fatigue, 94(2), 236–245 (2017).