PSI - Issue 42

Michael P. Milz et al. / Procedia Structural Integrity 42 (2022) 830–837 Michael P. Milz/ Structural Integrity Procedia 00 (2019) 000 – 000

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diagram, the influence of corrosion on the fatigue strength in the high cycle fatigue regime for uncoated sand blasting (I) specimens is illustrated. This influence increases with decreasing stress amplitude σ a , which is ultimately reflected in the run-outs, as the sand-blasting (I) specimens run-out at 240 MPa, while the ZnAl-coated (II-IV) specimens run-out at 280 MPa. In addition, all ZnAl-coated (II-IV) specimens show increased corrosion fatigue resistance, although a clear differentiation of the influence of MHP is not possible.

Fig. 6. Constant amplitude tests at 300 MPa: (a) Sand-blasting (I); (b) machine hammer peened MHP 2 (IV).

Fig. 7. S-N (Woehler) diagram for tested conditions: Sand-blasting (I), ZnAl-coating (II), MHP 1 (III), and MHP 2 (IV).

4. Conclusion and outlook The coupled process of twin wire arc spraying (TWAS) and machine hammer peeing (MHP) resulted in continuous and firmly adhering ZnAl coatings. MHP improves properties known to increase fatigue performance, such as reducing porosity and roughness while increasing hardness. Potentiodynamic polarization measurements show a beneficial shift in open circuit potential for the MHP (III, IV) specimens, which was further improved by adjusting the MHP parameter values for MHP 2 (IV). All ZnAl coatings protected the substrate and increased corrosion fatigue resistance in high cycle fatigue regime. Sand-blasting (I) specimens showed run-outs at a stress amplitude of 240 MPa, while coating systems (II-IV) obtained run-outs at 280 MPa. The measured open circuit potential during corrosion fatigue testing is suitable to identify the stress-dependent corrosion fatigue damage behavior. Accordingly, a correlation between mechanical and electrochemical measurements was demonstrated.