Development of ultra high strength steels based on spinodal decomposition

Spinodal decomposition in Fe-25 at%Co-9 at%Mo

“…To expand the considered "spinodal" region to lower Mo contents, Kozakai et al [12] and Doi et al [13] investigated FeeMo alloys with different Co contents. They calculated a shift of the spinodal to lower Mo contents due to alloying with Co. Fig.…”

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“…Lower JMA exponents n < 0.3 as found by the fit for peaks I and III (see Table 2) have no accordant explanation in literature. Spinodal decomposition has been mentioned to occur in Fe–Co–Mo ternary alloys similar to the one investigated in this work 1–3, 12, 15. If spinodal decomposition is the dominant effect causing heat of reaction I 12, using the JMA model for the analysis may yield ambivalent results, because it is only valid for linear growth 25.…”

“…This corresponds to the composition of the equilibrium µ‐phase. Chain‐like, rectangular features, as found in the samples aged to lower temperatures, have been related to spinodally formed microstructures 1–3 as well as to phase formations involving large coherency strains 4, 5. However, the exhibited morphology is not sufficient to determine the mode of decomposition, but the increasing concentration fluctuations indicate a spinodal behavior of the decomposition mode in the samples aged to 475, 500, and 540 °C 26.…”

“…Precipitation reactions during aging in the systems Fe–Mo and Fe–Co–Mo have been object of various investigations, which mainly concentrated on the development of intermetallic hardening phases. These phases were reported to form via spinodal decomposition 1–3 or classic nucleation and growth processes involving large coherency strains 4, 5. The alloy Fe–25 at%Co–9 at%Mo and similar compositions turned out to be promising for reaching very high hardness values (>65 HRC) upon aging, resulting in an enhanced technological interest in this material class 6–8.…”

Application of Photons and Neutrons for the Characterization and Development of Advanced Steels

“…During the course of the investigation of the Fe–Co–Mo alloy mentioned above15, 42, 48, 49 it became clear, that knowledge on the nature of the precipitation sequence is of utmost importance for the understanding of the development of the prevailing phases. In studies on the precipitation behavior of Fe–Mo and Fe–Co–Mo alloys it had been discussed if spinodal decomposition was the underlying mechanism of the occurring phase separation during the applied heat treatments 46, 71, 72. Another group investigating the precipitation behavior of Fe–Mo alloys distinguished two stages of the decomposition process and assigned the first stage to a nucleation and growth‐type formation of Guinier–Preston zones along the crystallographic <100> directions due to large coherency strains 45, 73.…”