A Kinetic Study of Order-Disorder Transition in Ni–Cr Based Alloys
Alloy 690 is a nickel-based alloy (60% Ni, 30% Cr, 10% Fe) used in nuclear Pressurized Water Reactors (PWR) for different components and welds (steam generator tubes etc.). They are subjected to thermal ageing up to 60 years which could lead to an order-disorder transition (Ni2Cr ordered phase formation) by a diffusion-assisted mechanism. This transformation might modify mechanical properties and is suspected to influence the stress corrosion resistance of the affected components. To study ordering kinetics, hardness, thermoelectric power (TEP) alongside transmission electron microscope (TEM) observations were conducted on Ni-33%Cr alloys with different iron contents (0–3 wt%) after various ageing thermal treatments. The ordering activation energies have been determined: they are found to be independent of the iron content. A correlation between macroscopic properties and TEM diffraction results is proposed. Finally, the distribution of iron between matrix and ordered domains was studied.
KeywordsOrdering reaction Nickel-based alloys Thermoelectric power Iron content
The authors gratefully acknowledge Yannick Fontaine and his team for sample preparation, Christian Vincent for thermal ageing and Sebastien Saillet for TEP data analysis. The TEM national facility in Lille (France) is supported by the Conseil Regional du Nord-Pas de Calais, the European Regional Development Fund (ERDF), and the Institut National des Sciences de l’Univers (INSU, CNRS). Financial support from EDF in the CSI project by Emilien Burger is also gratefully acknowledged.
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