PSI - Issue 82

Hang Su et al. / Procedia Structural Integrity 82 (2026) 131–137 H. Su et al. / Structural Integrity Procedia 00 (2026) 000–000

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amplitude due to the absence of critical void-type defects and the relatively homogeneous equiaxed grain morphology (Pan and Hong, 2019; Pan et al., 2024b). Overall, the comparison between AM and CP titanium alloys under R = –1 loading highlights the distinct fatigue responses arising from their different structural origins. The AM alloy exhibits a defect-controlled transition from surface to internal failure accompanied by a marked drop in fatigue resistance, whereas the CP alloy shows a microstructure-sensitive but monotonic decrease in stress amplitude with increasing life. The difference in S–N curve morphology demonstrates that the fatigue resistance of AM titanium alloys in the VHCF regime is primarily governed by the population and morphology of void-type defects, while for CP alloys it remains controlled by grain scale heterogeneity and slip behavior within the α+β matrix. This interpretation is further supported by recent probabilistic control-volume modelling which quantitatively links defect size distribution to fatigue life scatter in AM titanium alloys (Tao et al., 2024). 3. Fractographic characteristics

Fig. 2. Representative SEM morphologies for AM titanium alloys showing entire fracture surfaces (a,b) and crack initiation regions (c,d) of selected specimens: (a,c) R = –1, σ a = 500 MPa, N f = 1.09 × 10 5 cycles; (b,d) R = –1, σ a = 250 MPa, N f = 8.81 × 10 7 cycles.