G-phase strengthened iron alloys by design. (15th January 2020)

• Record Type: Journal Article
• Authors: King, D.J.M.; Yang, Mujin; Whiting, T.M.; Liu, Xingjun; Wenman, M.R.
• Is Part Of: Acta materialia. Volume 183(2020)
• Page Start: 350
• Page End: 361
• Publication Date: 2020-01-15
• Subjects: G-phase -- Solute clustering -- Density functional theory -- Duplex steels -- Ferritic; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2019.11.007
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Density functional theory (DFT) calculations were used to model G-phase precipitates of formula X6 M16 Si7 where X is Cr, Hf, Mn, Mo, Nb, Ta, Ti, V, W and Zr and M is either Fe or Ni. It was found that the occupancy of the d-orbital is correlated to the formation enthalpies of each structure. Past thermal expansion coefficient data was used to predict the lattice misfit between each G-phase and body centred cubic (BCC) Fe. All except Hf and Zr containing G-phases were predicted to have zero misfit between 581−843 K. Of the Ni containing G-phases, Mn6 Ni16 Si7 was predicted to have the most similar elastic properties to BCC Fe. DFT calculations of the substitution energies of Al, Cr Cu, Fe, Ge, Hf, Mo, Nb, P, Ta, Ti, V, Zr, and vacancies onto the Mn6 Ni16 Si7 G-phase from BCC Fe were performed. It was predicted that Cu, P and vacancies favour G-phase substitution. Suppression of the G-phase is predicted when Si content is reduced by half, at which point the BCC phase is favoured. It is hypothesised that including Zr to form a (Mn, Zr)6 Ni16 Si7 precipitate will allow for higher ageing temperature and expediate nucleation in an Fe alloy. Thermocalc was used to predict that a mixture of Febal Cr9 Ni4 Si2 (Mn0.6 Zr0.4 )1.2 (at.%) will produce a G-phase strengthened Fe alloy with potential for a good balance of strength, ductility and oxidation/corrosion resistance at room temperature. This alloy composition was experimentally determined to precipitate the G-phase in ≤24 h with cube-on-cube orientation to the BCC Fe matrix. Graphical abstract: Image, graphical abstract