Abstract
Ni based superalloys are adopted as base materials for critical hot gas path components of gas turbines. Knowledge of the evolution of the microstructure is very important for gas turbine producers in order for them to fully predict component behaviour in service. Quantitative EBSD measurements have been performed to evaluate the local strain condition of the material after test on creep and LCF testpieces of two Ni based superalloys. The Cross-Court software has been used to quantitatively analyse EBSD patterns by means of the cross-correlation method developed by Wilkinson et al. The results of the quantitative analyses enable microstructural characterisation to be completed and the mechanisms that describe material property evolution to be better understood. In addition some measurements have been extended to real components after service and the results have been correlated to FE simulations.
Highlights
Ni based superalloys are used as structural materials for critical components in aero and industrial gas turbines because of their high resistance to deformation
The HR-Electron backscatter diffraction (EBSD) measurements determined by means of the cross-correlation method are here shown and discussed, while the other aspects of the microstructural evolution are only briefly reported for comparison with the damage evaluation through Cross-Court software
It was not possible to apply these thresholds to all the observations from all the maps, in particular for ex-service materials, but the mean angular error (MAE) and peak height (PH) maps have been used to provide the basis of comments on the results
Summary
Ni based superalloys are used as structural materials for critical components in aero and industrial gas turbines because of their high resistance to deformation. The gas turbine producers should know the materials behaviour in this kind of operating regime, in terms of microstructural damage evolution This knowledge is fundamental to understanding the mechanisms that determine the formation of physical damage and can be exploited to recognise the different damaging phenomena in ex-service material. Ni based superalloys are characterised by a composite microstructure, composed of an austenitic γ matrix, strengthened by solid solution elemental substitution, and a high volume fraction γ phase precipitate distribution (50–70%, depending on the composition of the alloy). The peculiarity of these precipitates is that they are intermetallic phase Ni3Al, with an ordinate structure, and coherent with the γ matrix. The cross-correlation analysis has been extended to ex-service materials and the results have been compared with FE simulation predictions
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