THE CREEP FATIGUE OF TURBINE DISC ALLOYS

摘要

The drive for improved temperature capability from turbine disc alloys has led to an increased interest in the contribution of time-dependent mechanisms to high temperature fatigue crack growth. This study was conducted to investigate the relative contribution of these mechanisms and the effect of cycle frequency on crack growth. Testing was conducted under conditions of constant load and ΔK at 725°C in air and vacuum and at an R-ratio of 0.5. The results demonstrate that the relative contribution of these mechanisms depended on applied in stress intensity range. Furthermore, a decrease in frequency caused an increase in crack growth rate per cycle (da/dN.) This increase in da/dN was most significant for tests conducted in air and a dramatic increase in da/dN for both constant load and △K conditions was associated with a transition to an intergranular crack growth mode.