Speaker
Description
Nitrogen is a well-known gamma-stabiliser in austenitic steels, also responsible for significant improvement of mechanical resistance of these materials. Most of its interest is found when this interstitial element is dissolved in the matrix. Its impact in austenitic high-entropy alloys (HEAs) is already largely reported in the literature. However, nitrogen can also take the form of nitrides by reacting with a constituting element of the matrix, though, few papers studied the impact of precipitation on the alloy’s behaviour. This study focuses on a cobalt-free, non equimolar CrFeMnNi HEA doped with nitrogen. A series of alloys was cast under a nitriding atmosphere to promote nitrogen absorption into the liquid alloy up to 0.45 wt. % (1.7 at. %).
Microstructure and phase stability were investigated through SEM/EDX and TEM observations and analyses. The impact of nitrogen in solid solution on mechanical properties has been assessed with hardness and tensile tests. Precipitation was then studied after several heat treatments. Formed nitrides, in agreement with thermodynamics predictions (Thermocalc Software), were successfully indexed as Cr2N (TEM and XRD analyses). Impact of nitrides on mechanical properties and recrystallization phenomena was also analysed.
Tayloring the properties of N-doped HEA through an appropriate heat treatment is possible. When in solid solution, nitrogen is confirmed to be efficient to increase mechanical resistance without affecting ductility. Not surprisingly, when intergranular nitrides are present, a significant decrease of toughness is observed. However, fine precipitates help refining the microstructure during a recrystallization process.
| Speaker Country | France |
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