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Monte Carlo simulations of Cu/Ni鈥揝i鈥揗n co-precipitation in duplex stainless steels

by William Frazier, Timothy G Lach, Thak Sang Byun
Publication Type
Journal
Journal Name
Acta Materialia
Publication Date
Page Numbers
1 to 12
Volume
194
Issue
5

First-Passage Kinetic Monte Carlo (FPKMC) simulations of species migration in duplex stainless steels were performed in order to establish relationships between alloy content, segregation behavior, and the formation of Ni鈥揝i鈥揗n rich particles in cast duplex stainless steels during thermal aging. The Ni鈥揝i鈥揗n-rich second phase forms after extended aging at reactor operating temperatures and degrades alloy properties. Simulations of Ni鈥揝i鈥揗n cluster formation were validated through comparison with experimental results obtained through Atom Probe Tomography (APT) on similar alloy compositions, identifying several trends. First, Cu promotes the formation of Ni鈥揝i鈥揗n clusters, but only when Ni or Mn prefer segregation to the surface of Cu particles; without the segregation of these species, the critical composition for the clusters to form was not achieved. Second, the width of precipitate-denuded zones near 纬/未 interfaces increases with decreasing Cu content. This finding was in strong agreement with APT and Scanning Transmission Electron Microscopy results, further validating our model. Finally, our model predicts that Ni鈥揝i鈥揗n cluster formation will be the most extensive when the Si:Mn ratio is approximately 1:1 and the least extensive when one of these key elements is less concentrated (Mn 鈮� 0.5 at.% or Si 鈮� 0.5 at.%). The implications of these results on how to improve alloy properties are discussed.