G-phase strengthened iron alloys by design

Abstract

Density functional theory (DFT) calculations were used to model G-phase precipitates of formula X6M16Si7 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, Mn6Ni16Si7 was predicted to have the most similar elastic properties to BCC Fe. DFT calculations of the substitution energies of Al,

Hydrogen Embrittlement Characterization of 1.4614 and 1.4543 Martensitic Precipitation Hardened Stainless Steels

“…The G-phase is clearly highlighted after matrix subtract mode, and a cubecube relation is shown between G-precipitate with the martensitic matrix (same colors on orientation maps) as seen in Figure 6. Such relations between G-phase and ferrite have already been found previously in the literature on larger G-phase silicide of about 20 to 50 nm [23,24].…”

Precipitation behavior in G-phase strengthened ferritic stainless steels

“…The convergence criterion for electronic convergence was 10 −6 eV and for geometry optimization was 10 −4 eV. The formation enthalpies of the disordered structures were computed using the same methodology as previous performed on these systems [21,30]. For the (NixFe1-x)16M6Si7 G-phase/BCC and (NixFex-1)2MSi L21 structures, the formation enthalpies were interpolated between end members except in the case for M = Mn in the G-phase where enthalpies were taken from previously published calculations [31].…”

“…One of the benefits of the G-phase strengthening is the potential for conserving the ductility of the alloy due to its coherency with the ferritic matrix. Recently, it has been theorized that it may be possible to fine-tune this coherency through altering the chemical composition of the G-phase [21]. This concept presents a significant number of G-phase compositions that could potentially be exploited in advanced Fe-base alloys.…”

“…Seventeen different G-phase chemistries have been theoretically investigated in our previous studies, and preliminary investigations of four different G-phase precipitating alloys (Ni16Zr6Si7, Ni16Ti6Si7, Ni16Nb6Si7 and Ni16Ta6Si7) have been investigated experimentally [21][22][23][24].…”

The effect of salt loading on chloride-induced stress corrosion cracking of 304L austenitic stainless steel under atmospheric conditions

“…To identify the cause of difference in stabilities between Ni vs Fe containing G-phase compositions, the electronic structures are examined by plotting the l-decomposed projected density of states (PDOS) of four compositions W6(Ni/Fe)16Si7 and Zr6(Ni/Fe)16Si7, which represent the least and most stable non-magnetic structures, respectively, see Fig 1 . The total density of states (TDOS) of all compositions are plotted in Fig. A2 and complete datasets pertaining to all l-decomposed X6(Ni/Fe)16Si7 structures can be found in ref [43]. In all cases, there is strong hybridisation in the Si-p, Fe/Ni-d and Xs, -p and -d orbitals.…”