Issue 78

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

of the specimens and their increased fatigue cracking resistance for longer periods in comparison with those for the heat treatment 1.

Figure 13: The dependences of the relative duration of crack propagation period N p / N f (a) and K I,max value (b) on the fatigue durability N f , as well as the fatigue striation spacing δ on K I,max value (c) for the specimens cut out from the samples with the heat treatments 1 and 2.

C ONCLUSIONS

I

n this study, the effect of the aging temperatures on the mechanical and fatigue properties of the Ti-5Al-5V-5Mo-1Cr 1Fe titanium alloy treated by the RSR was investigated. Increasing aging temperature from 450 up to 520 °C gave rise to coarsening of the microstructure and enhancing of the volume fraction of the  -phase from 58 to 71 %. As a result, the ultimate tensile strength reduced from 1695 down to 1570 MPa with the increase in tensile strain from 3 up to 6 %. Aging at the higher temperature improved the fatigue performance of the specimens tested at the frequency of 5 Hz, which was most pronounced for the maximum stresses at a cycle below 900 MPa. The fatigue limit typical for titanium alloys in the HCF region was observed at cyclic stress level of 800 MPa. The regularities of fatigue crack initiation and propagation in the HCF mode for the titanium alloy after two considered heat treatments were found. For the applied aging temperatures, the differences in the fatigue failure mechanisms were revealed, including the changes in the locations of origins, the shapes of the fronts of surface cracks, the ratios of their semi axes, and the lengths along the minor axis of the semi-ellipses. According to the results of the fractographic examinations, the values of fatigue striation spacing at the transition to the final fracture stage were higher for the aging temperature of 520 °C compared to those for 450 °C, which evidence of the obtaining of the material in a state with a higher resistance to fatigue crack growth. Because of longer crack nucleation period for the aging temperature of 520 °C compared to those for 450 °C, the alloy in the former case reflects a greater resistance to damage accumulation before crack nucleation.

257