Abstract
Practical usefulness of a marker-technique to the examination of crack growth behaviour of Ni-alloys at 500 to 750 °C. Creep resistant and creep crack growth tolerant Nickel alloys are required for turbine rotor shafts and discs in advanced industrial gas turbines and future steam turbines at very critical conditions. There are very limited results on crack behaviour in Nickel base alloys in the open literature, some of the postulated effects of loading conditions are contradictory and no information is given concerning the use of marker-technique for crack growth evaluation. For the expected service temperature 500 to 750°C the creep-fatigue crack growth in two typical Ni-alloys were investigated, the alloys Inconel 617 and PM N18. The influences of proof-temperatures and of the environments (open air versus vacuum) and the applicability of the marker-technique are discussed for these representative of Nickel alloys, i. e. for solid state hardened Inconel 617 and y'-hardened PM N18. For both proof temperatures there is no stringent effect on the crack growth rate in the Paris region, however, a distinctly influence of the environment on crack initiation has been detected. Furthermore, the conditions for a useful application of the marker technique in this temperature range are proposed in this contribution.
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