Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. Surface Quality
3.2. Microstructural Development of the Heat-Affected Zone (HAZ)
3.3. Fatigue Results and Crack Initiation
4. Conclusions
- The surface relief introduced by the non-optimized laser-cutting influences the fatigue behavior of Ti-6Al-4V-ELI significantly. For the process parameters featured in this study, fatigue strength of the as-cut condition results in a drastic decrease of the fatigue strength compared to the additionally surface-treated condition. However, the difference in fatigue strength observed in this study will be controllable by optimizing the laser-cutting parameters.
- The main reason for the superior fatigue strength of the post-processed conditions is a minimized surface roughness, which in turn is responsible for higher resistance against fatigue crack initiation on macro- and micro-notches originally caused by the laser-cutting.
- The process of barrel-grinding after the laser-cutting was effective but revealed retained surface roughness in the center area of the cutting edges, which acts as preferred crack initiation sites compared to the particularly rounded sample corners.
- Mechanically polished samples always failed at or near the sample corners, which is caused by a stress concentration on these sites.
- The HAZ consisting of martensitic α’ and β along distinctive surface and subsurface zones was analyzed and does not play a significant role in early fatigue failure, which instead was dominated by the surface roughness. Nevertheless, the applied mechanical post-processing led to an almost complete removal of the HAZ.
- To avoid early fatigue failure in the application, an optimization of the laser-cutting parameters is crucial in order to obtain better surface quality. This allows the required post-processing to improve the surface roughness further and, therefore, the fatigue strength. However, both processes, laser-cutting and mechanical post-processing, have to be optimized in the dependence of the specific alloy composition and fatigue behavior of Ti-6Al-4V-ELI.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Cutting Parameters | Laser Power | Cutting Speed | Spot Size | Laser Beam Quality | Cutting Gas | Nozzle | Focal Distance |
---|---|---|---|---|---|---|---|
Used parameter set | 3 kW (λ = 1035 nm) | 25 m/min | 150 µm (Focal spot on the surface) | M2 = 14 | Argon (6 bar) | Single head-Conical (2.0 mm) | 6 inch |
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Reck, A.; Zeuner, A.T.; Zimmermann, M. Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing. Metals 2019, 9, 843. https://doi.org/10.3390/met9080843
Reck A, Zeuner AT, Zimmermann M. Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing. Metals. 2019; 9(8):843. https://doi.org/10.3390/met9080843
Chicago/Turabian StyleReck, André, André Till Zeuner, and Martina Zimmermann. 2019. "Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing" Metals 9, no. 8: 843. https://doi.org/10.3390/met9080843
APA StyleReck, A., Zeuner, A. T., & Zimmermann, M. (2019). Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing. Metals, 9(8), 843. https://doi.org/10.3390/met9080843