Manipulation of solute partitioning mechanisms for nanocrystalline stability. (15th April 2021)

• Record Type: Journal Article
• Authors: Zhou, Xuyang; Gupta, Ankit; Tucker, Garritt J.; Thompson, Gregory B.
• Is Part Of: Acta materialia. Volume 208(2021)
• Publication Date: 2021-04-15
• Subjects: Nanocrystalline stability -- Segregation -- Precipitation -- Grain boundary -- Zener pinning; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2021.116662
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: We describe an approach that enables the activation of two distinct nanocrystalline stability mechanisms in the same Ni(P) alloy by controlling the annealing temperature and chemical composition. Using a two-step heating process, it is shown that a low temperature first stage anneal (350 °C/1 h) drives the solute in a Ni-1at%P alloy to decorate the grain boundaries (GBs) in achieving thermodynamic stabilization at higher temperatures (550 °C). Atom probe tomography reveals a very low contamination level of species (< 0.2 at.%) that concretely demonstrates this stability mechanism. If the annealing avoids this initial, low temperature step and directly reaches the higher temperatures (550 °C), the solute precipitates a stable Ni3 P phase pinning the GBs. Until this secondary phase forms, the grains coarsen significantly. On changing the alloy chemistry to Ni-4at.%P, in either the two-step (350 °C/1 h then 550 °C) or single-step (directly to 550 °C) anneal, the solute precipitates the Ni3 P phase and engages the Zener pinning mechanism. Comparing the two stabilization mechanisms, thermodynamic versus Zener pinning, the thermodynamic mechanism yields a more refined, stable grain size with annealing temperature even though the pinning strength from a uniform distribution of solute is found to be lower than that of the Zener mechanism. These results are discussed using complementary atomistic simulations. Graphic abstract: Image, graphical abstract