Thermo-mechanical fatigue and fracture of INCO718

A new thermo-mechanical fatigue facility has been commissioned in the Materials Research Centre, University of Wales, Swansea. The equipment utilises an induction heating/forced air cooling thermal cycle and is capable of tension and torsion mechanical loading. The paper highlights experience in using this system for strain control TMF testing on INCO718. The coil design, gripping system and calibration procedures introduced are discussed in relation to the form and accuracy of the data generated. To illustrate, detailed hysteresis loops are presented for thermal cycles from 300 °C to 680 °C and a range of strains for in and out of phase loading conditions. The effectiveness of pyrometers and thermocouples in monitoring and controlling the applied temperature is discussed. The significance of emissivity values in these measurements is assessed. The life data generated are compared with isothermal fatigue measurements on the same alloy.