Life prediction for the titanium alloy IMI 834 under high temperature creep-fatigue loadings

In the present investigation the life behavior of the titanium alloy IMI 834 under loading conditions which are close to real service was considered. Different types of creep-fatigue loadings were applied at 600 deg C, i.e. balanced and unbalanced cycles with different ramping times into tension and into compression and stress hold Strain Range Partitioning (SRP) cycles. The testing was performed in laboratory air. The results of the creep-fatigue tests showed that life was reduced by the different types of creep-fatigue cycles. In the stress hold tests the mean stresses had a pronounced influence on life. The observed life of the stress hold SRP cycles could be predicted within a factor of plus /minus2 of actual life by frequency-modified approaches. If mean stresses were considered in terms of maximum tensile stress or by a modified Morrow approach, life predictions remained within a factor of plus/minus1.5 of the actual test results. A SRP approach which was frequency modified in the present study led to life predictions which fell within a band of a factor of plus/minus1.35 of the actual test results.