Abstract The turbine blades play a crucial role in the efficiency of the steam turbines system, which can also lead to safety and economic implications in a catastrophic failure. The propagation of fatigue cracks is a relevant issue, especially if there are safety issues involving human life or the environment or significant economic losses. This work investigated the failure of a turbine blade of a 25 MW cogeneration power plant. One found several deformation marks and debris in the primary crack origin at the blade's base. They were responsible for the fretting fatigue type wear. The blade material matches the composition of X20CrMo13 steel; however, the hardness shows a higher average value (250±4.7) than typical standard values of 220–240 HB.

The aim of this study was to evaluate and compare the effect of low temperature and saline environment on the fatigue crack growth behavior of the AA7050-T7451 Al alloy and the recently developed AA2050-T Al-Cu-Li alloy. Fatigue at room and low temperature and corrosion-fatigue tests were carried out using an applied stress ratio (R) of 0.1, 15 Hz frequency (air at RT and –54 °C) and 1 Hz frequency (seawater fog) using a sinusoidal wave form. In the near-threshold region, in air and at RT it was found a ΔKth = 2.9 MPa.m1/2 for AA2050-T84, in saline environment this value increased to ΔKth = 4.9 MPa.m1/2, due to closure effect through wedge effect by the corrosion products. At the beginning of the Paris-Erdogan region, the crack closure effect was not present for the AA7050-T7451, but persisted for the AA2050 Al-li alloy. It was observed that both alloys were equally affected by temperature reduction. When the saline environment is considered it was observed that the AA7050-T7451 presents lower m value (2.6) than the one for AA2050-T84 (3.4), meaning a lower FCG rate variation with ΔK, however it presented the highest C value, as a consequence the worst FCG behavior.