Crack Growth Behaviour of An Advanced Nickel Disc Alloy Under Thermo-Mechanical Fatigue Conditions

The increasing operating temperature of aerospace gas turbines is beginning to result in the fracture critical discs experiencing new combinations of thermal and mechanical stresses during operation of new engine designs. This change is leading the disc material to encounter thermo-mechanical fatigue conditions more and has required the development of improved life prediction methods to account for this change in operating conditions.

To assist in the validation of the life prediction methods and to enable a better physical understanding of the crack growth behaviour under thermo-mechanical fatigue conditions to be obtained a facility has been recently commissioned to specifically enable crack growth measurements under representative conditions. This paper very briefly reviews the development of this test facility.

The initial tests have been performed on the advanced nickel disc alloy, RR1000 in two microstructural conditions. Thus the temperature has been cycled between 400^oC and 700^oC, whilst a simplified load cycle has also been applied. The fatigue crack growth rate measurements have demonstrated a significant benefit from the use of a large grain size microstructure, compared with the conventional fine grain structure. The fracture path and underlying microstructural features have been examined and correlated with the change in crack growth rates.