Issue 77

A. Trombetta et alii, Fracture and Structural Integrity, 77 (2026) 71-88; DOI: 10.3221/IGF-ESIS.77.06

SEM images of fatigue fracture surfaces in Fig. 17 show classical initiation (I), propagation (P) and final fracture (R) regions: low-magnification images of the propagation zone reveal smooth crack surface, while high magnification ones show striations, especially for BA, and secondary cracks. For all conditions high magnification images of final overload fracture (R), not reported in this paper, show a ductile behaviour with equiaxed dimples.

Figure 18: SEM examination of fatigue fracture surface for the different conditions (A, STA, BA and BSTOA) with detail of the propagation zone at high magnification. I = Initiation zone; P = Propagation zone; R = Final fracture zone. Fatigue trends align with literature [5,24]: fine lath microstructures like STA and BSTOA yield higher endurance due to crack initiation delay, while BA, due to the presence of lamellar colonies, despite slower crack growth rate as illustrated in Fig. 18, shows a reduced fatigue limit due to early crack initiation. To summarize the entire experimental campaign, the radar map in Fig. 19 gathers the main mechanical properties of the Ti 6Al-4V alloy under the different applied heat treatment conditions.

Figure 19: Radar map for heat treatment selection of Ti-6Al-4V.

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