A review of thermo-mechanical fatigue behaviour in polycrystalline nickel superalloys for turbine disc applications

Within the gas turbine engine, the high transient thermal stresses resulting from throttle movement from idle to high settings give rise to the phenomenon of thermo-mechanical fatigue (TMF). These effects have been widely explored for turbine blade materials, typically single crystal nickel alloys. More recently however, a combination of thinner disc rims and further increases in turbine entry temperature has led to a situation where TMF in disc materials cannot be ignored. Turbine discs will usually be manufactured from polycrystalline nickel alloys, and as such it is now considered critical that TMF effects in this system of alloys is fully characterised. The current paper seeks to summarise the published work on TMF in polycrystalline nickel alloys for turbine disc applications, whilst introducing recent work at Swansea University. Previous research has concentrated particularly on the differences between in-phase (IP) and out-of-phase (OP) loading. The current work from Swansea indicates that this approach is overly simplistic and that for a complete evaluation of the alloy, intermediate phase angles should also be considered.