Issue 78

A. P. Soldatenkov et alii, Fracture and Structural Integrity, 78 (2026) 248-259; DOI: 10.3221/IGF-ESIS.78.15

phenomenon could be associated with the increase in the volume fraction of the  -phase, which possessed a higher value than that of the β -phase [23,24]. It should be noted that, despite the decrease in the ultimate tensile strength for heat treatment 2, its level remained greater than those for a large number of metastable titanium alloys after various thermomechanical treatments [25,26].

b

c

  MPa

a

1

1000 1250 1500 1750

2

250 500 750

1-RSR+450 о С , 5 h 2-RSR+520 о С , 5 h

0123456789 0

 

100 µm

100 µm

Figure 4: The stress-strain curves (a) in addition to the SEM micrographs of fracture surfaces (b, c) of the specimens cut out from the samples of heat treatment 1 (b) and 2 (c).

Treatment

Yield stress σ 0.2 , MPa

Ultimate strength σ UTS , MPa Tensile strain δ , %

1600 ± 10

1695 ± 10

3.0 ± 0.5

RSR + aging 450  C, 5 h

RSR + aging 520  C, 5 h 6.0 ± 0.5 Table 3. The mechanical properties of Ti-5Al-5V-5Mo-1Cr-1Fe alloy after radial-shear rolling with subsequent aging at different temperatures. For heat treatment 1, the fracture surfaces possessed the ductile pattern (Fig. 4b), where regions of 30–50 µm in size with barely visible dimple reliefs were found along with pronounced dimpled zones. However, the only ductile areas with the distinct dimple relief were observed for heat treatment 2 (Fig. 4c), corresponding to higher ductility. Overall, these patterns were fully consistent with the mechanical properties of the specimens determined in the tensile tests. Fig. 5 shows fatigue S-N curves of the tested specimens, according to which heat treatment 2 prolonged their fatigue durability, especially at low stress levels. At the cycle stress of 800 MPa, the tested specimen did not fail after more than 10 6 cycles, while the one after heat treatment 1 fractured at less than 3  10 4 cycles (Fig. 5). 1510 ± 10 1570 ± 10

Figure 5: The fatigue S-N curves of specimens cut out from the samples of heat treatment 1 and 2.

252