PSI - Issue 71

T. Vivekananda Swamy et al. / Procedia Structural Integrity 71 (2025) 111–117

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The microstructure of the as-received sample was captured under an optical microscope. The fractographs of the fractured specimens were obtained using a JEOL 6380A Scanning Electron Microscope (SEM). Further analysis was performed on the same SEM images of the samples subjected to various loading conditions and temperatures.

3. Results 3.1. HCF tests

S-N curves for the results obtained from the HCF tests conducted on as-received Ti-6Al-4V specimens for RT and 150 ℃ are shown in Fig. 3. These curves were plotted with normalized number of cycles to failure. The fatigue strength is found to be reduced with an increase in temperature.

Fig. 3 S-N Curves for RT and 150 ℃ Reduction in fatigue strength of 50 MPa from RT to 150 ℃ for Ti-6Al-4V alloy tested is observed. The reduction in fatigue strength at 150 ℃ is owing to lower crack initiation resistance and can also be due to lower yield strength at increased temperatures. It is observed that at a low number of cycles (<10 5 ), the effect of temperature on fatigue life is significant as compared to the high number of cycles (>10 5 ). At maximum stress of 1000MPa, a drastic reduction in fatigue life of 99.89% is seen from RT to 150 °C tests. A minimum reduction in fatigue life of 66.45% is observed from RT to 150 °Cat a maximum stress of 900 MPa. 3.2. Fractographic studies Fig. 4 and Fig.5 display SEM fractographic images of failed specimens tested at RT and 150 ℃ , respectively. Fractographic studies were carried out at RT on two stress levels. The fractographs of this specimen subjected to a maximum stress of 950 MPa are shown in fig 4 (a), (b), and (c). The same for other specimen subjected to a stress of 1000 MPa are shown in Fig. 4 (d), (e), and (f). Additionally, fractographic investigations were conducted for two more stress levels at 150 °C.