WEB Overheating microstructural study of nickel-based superalloys from turbine blades of aircraft enginesWednesday (27.05.2020) 16:17 - 16:17 Poster Room Part of:
Nickel-based superalloys, especially single-crystal (SC) ones, are employed in critical materials for turbine blades used in the aviation, aerospace and gas engines. High temperature strength capabilities similar to those SC alloys have been achieved in a second-generation columnar grain alloys. Advanced turbine blades, where high-temperature strength and creep life are required, are subjected to degradation during service by combined effects of temperature, mechanical stresses and environmental conditions.
The purpose of this paper is to compare the effects produced by overheating on two blades manufactured in two different materials, PWA 1440 and PWA 1426. The first one corresponds to a SC alloy and the second one to a columnar grain superalloy. The typical microstructure of this type of superalloys consists of ɣ' rectangular precipitates (Ni3Al) into the Ni ɣ matrix, which has a face-centered cubic structure (FCC). It could also present ɣ/ɣ' eutectic-islands and, occasionally, areas with a coarser ɣ' phase within the matrix. In addition, carbides could be occasionally observed due to the carbon combination with other elements such as Cr, Ta and Hf, around the interdendritic arms in the PWA 1426 superalloy microstructure. Overheating would lead to modifications in the superalloy microstructure, producing changes in the ɣ' precipitates concentration, size and distribution, ɣ/ɣ' eutectic coalescence and dissolution, and carbides decomposition and dissolution.
In order to determine if overheating has occurred in the analysed blades, metallographic samples were prepared for microstructural characterization and observed in an optical microscope. Carbides were analysed by EDX spectrometer coupled to a FE-SEM microscope. Furthermore, replicas were prepared for the characterization of the superalloys phases and precipitates using the selected area electron diffraction technique (SAED), coupled to a TEM microscope. Finally, chemical analysis was carried out by an XRF spectrometer.
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