Isothermal and thermomechanical fatigue of titanium alloys

LCF and TMF tests were conducted on Ti6242 and on the intermetallic TiAl alloy TNB-V2 between 350–650 °C and 550–850 °C, respectively. A continuous life reduction of Ti6242 was observed with increasing temperature. On contrary, temperature does not have a systematic influence on life for TNB-V2. Life description based on Basquin-Coffin-Manson illustrates the small contribution of plastic strain to fatigue life of TNB-V2. The transition cycle number, which represents the transition from plastic strain to stress controlled fatigue life, was found to be 4 for TNB-V2 at 550 °C, while it is 409 for Ti6242. Tests in vacuum demonstrated a strong influence of the environment. TMF tests showed that TNB-V2 is very susceptible to out-of-phase loading.