Abstract
In situ X-ray diffraction and transmission electron microscopy has been used to investigate René 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of γ′ precipitates, their volume fraction, evolution of the lattice parameter of γ and γ′ phases and misfit parameter of γ′ in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of γ′ precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100–1250 °C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both γ and γ′ phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient.
Highlights
Nickel-based superalloys, due to their ability to keep high strength, very good hot corrosion and oxidation resistance during long-term service, are commonly used in high-homologous temperature applications
Specimens were heated at a rate 100 ◦ C/min, held for 30 s in order to homogenise the temperature in the sample volume, and the diffraction measurement was started
L γ+γ' transformation took place in a temperature range, so it was monovariant in nature.islands
Summary
Nickel-based superalloys, due to their ability to keep high strength, very good hot corrosion and oxidation resistance during long-term service, are commonly used in high-homologous temperature applications. It was 1140 ◦ C, whereas heating at 300 ◦ C s−1 caused a displacement up to 1265 ◦ C The aim of this investigation was to characterise the stereological parameters and the chemical composition of γ0 precipitates in René 108 in the initial condition, and show their behaviour during dissolution at high-homologous temperatures, by studying the evolution of lattice parameter of γ and γ0 and the resultant misfit parameter. These changes are especially important for several reasons. This work was carried out in order to complete this lack of useful information
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