Low-cycle fatigue performance and life prediction of a P/M nickel-based superalloy with artificial surface defect at elevated temperature

Abstract

P/M nickel-based superalloys are widely used in turbine disks, defects such as inclusions and surface scratches inevitably arisen from manufacturing process will exert negative influences on the low-cycle fatigue performance of superalloys and make traditional life prediction method no longer reliable. The residual fatigue life in presence of defect is an important performance index for disc alloy in damage tolerance design criteria. In this work, LCF tests of FGH96 specimens with artificial surface defect were conducted at 600℃, 650℃, 700℃ and room temperature, the size of the defect is determined in accordance with the minimum flaw size which can be detected by NDT technique. The results show that the LCF life of the specimens with artificial surface defect decreases significantly with the increase of temperature and size of defect. Microscopic characterization technique SEM and EDS were executed to investigate the failure mechanism of the specimens, different mechanisms of crack initiation from artificial surface defect at room and elevated temperature were discussed. And then life prediction based on fracture mechanics was carried out by ABAQUS-FRANC3D co-simulation. This method allows that SIF can be conveniently calculated by finite element method and it is applicable to analysis of arbitrary engineering structure. Good life prediction results which fall within double dispersion band of experimental lives were obtained at elevated temperature, but the predicted life is excessively conservative at room temperature because the crack initiation process accounts for a large proportion of fatigue life. It seems that life prediction method based on fracture mechanics is more applicable to specimens with surface defect at elevated temperature due to the shorter crack initiation process. This work has reference significance to the damage tolerance analysis of turbine disks.