Evaluation of high temperature behaviour of a new low density nickel base superalloy for aeronautical gas turbine blade applications

The aim of the following investigation is to evaluate the creep and low cycle fatigue (LCF) properties of DD417G, a new low density, Re free, nickel base superalloy for aeronautical gas turbine blades, developed by the Institute of Metals Research (IMR-CAS) Shenyang, PRC. Constant load creep tests have been carried out from 750 up to 1000°C, at stresses between 90 and 750 MPa to produce time to rupture up to 6000 hours. The creep behaviour of DD417G has been analysed in terms of times to rupture and shapes of the creep curves in function of the applied stress/temperature. Time to rupture: the experimental results are compared with competing alloys taking into account the low density of the here presented alloy. Creep curve shape: the experimental creep curves are characterised by a long predominant tertiary/accelerating creep, where the creep strain rate increases linearly with the accumulated strain, while the primary creep is small. The LCF tests, performed at 750°C and 850°C in longitudinal strain controlled conditions, have evidenced a fairly stable cyclic response. Basquin and Coffin-Manson relationships can adequately predict the fatigue life of the alloy. Examination of fracture surfaces revealed that fracture, induced by creep damage, is internal and mainly starts from eutectic island and pore-initiated cracks. However, fatigue damage starts on the external surface and propagates inward in stage II mode.