PSI - Issue 68

Mirko Teschke et al. / Procedia Structural Integrity 68 (2025) 936–941 M. Teschke and F. Walther / Structural Integrity Procedia 00 (2025) 000–000 By equating Eq. (1) and (2) and transforming them, Eq. (3) can be generated, which describes the stress range ∆ as a function of defect size ! , defect position , and number of cycles to failure / . Since the Paris coefficient C and the exponent m were previously determined, Eq. (3) can be used to generate local defect-based (artificial) S-N curves that quantify the influence of defects on fatigue strength. ∆ ( ! , , / )= A ! ∙ ∙ ( 2 − 2)F 0- ∙ √ ∙ ! ∙ / ) 0- (3) Fig. 5b shows a local defect-based S-N curve calculated using this method for surface defects. The comparison with the data points from the experiment shows a very high level of correlation. The know-how shown here is appropriate for taking the influence of defects into account in the design of AM components, for estimating the fatigue performance during process monitoring, or in post-production examinations (e.g. computer tomography). 4. Conclusions and outlook In this study, the titanium aluminide alloy TNM-B1, manufactured by electron beam powder bed fusion and laser based directed energy deposition, was characterized both in as-built condition and after hot isostatic pressing. Three material conditions were investigated using metallographic techniques, fatigue tests at room temperature and 800 °C, and SEM fractography. The test temperature had no significant effect on fatigue strength, while the HIP treatment resulted in a significant increase in fatigue strength. A high correlation between fatigue life and defect size was found. In the as-built condition, lack-of-fusion defects and gas pores were identified as the main causes of failure. After HIP, although the defect size was significantly reduced, pores and microstructural defects mainly lead to failure. The Murakami and Shiozawa approaches were used to model the relationship between fatigue life and defect size. This correlation held overall material conditions and test temperatures. In addition, it was possible to generate local defect based S-N curves for theoretical defect sizes, allowing an assessment of the effect of different defects on fatigue behavior. Acknowledgements The authors thank the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) for its financial support within the research projects “Microstructure and defect controlled additive manufacturing of gamma titanium aluminides for function-based control of local materials properties” (project number: 404665753) and “Development and validation of a methodology for in-situ detection and model-based evaluation of manufacturing defects in electron beam powder bed fusion” (project number: 528264362). The authors further thank the DFG and the Ministry of Culture and Science of North Rhine-Westphalia (Ministerium für Kultur und Wissenschaft des Landes Nordrhein Westfalen, NRW) for their financial support within the Major Research Instrumentation Program for the Electron Probe Microanalyzer (project no. 445269564, INST 212/461-1 FUGG). References [1] Y. Murakami, Effects of small defects and nonmetallic inclusions on the fatigue strength of metals, JSME international journal. Ser. 1, Solid mechanics, strength of materials 32 (1989) 167–180. https://doi.org/10.1299/jsmea1988.32.2_167. [2] K. Shiozawa, L. Lu, Effect of non-metallic inclusion size and residual stresses on gigacycle fatigue properties in high strength steel, AMR 44 46 (2008) 33–42. https://doi.org/10.4028/www.scientific.net/AMR.44-46.33. [3] H. Clemens, S. Mayer, Intermetallic titanium aluminides in aerospace applications – processing, microstructure and properties, Materials at High Temperatures 33 (2016) 560–570. https://doi.org/10.1080/09603409.2016.1163792. [4] H.A. Soliman, M. Elbestawi, Titanium aluminides processing by additive manufacturing – a review, Int J Adv Manuf Technol 119 (2022) 5583–5614. https://doi.org/10.1007/s00170-022-08728-w. [5] M. Teschke, J. Moritz, J. Tenkamp, A. Marquardt, C. Leyens, F. Walther, Defect-based characterization of the fatigue behavior of additively manufactured titanium aluminides, International Journal of Fatigue 163 (2022) 107047. https://doi.org/10.1016/j.ijfatigue.2022.107047. 941 6