NEW METASTABLE TERNARY Fe_7.5MoC_1.5 PHASE: NANOSIZED STATE AND Mn-Like polymorphism

Abstract

The Fe–Mo–C spinning ribbons produced by rapid melt cooling at a rate of ~ 106 K/sec have been studied by transmission electron microscopy. The metastable ternary phase of stoichiometry close to Fe_7.5MoC_1.5 has been found for the first time. Under conditions far from equilibrium, this phase behaves like a metallochemical and structural analog of elementary Mn under thermodynamic equilibrium conditions, namely: it can appear in crystalline structures, isostructural to γ-, β-, and α-polymorphous modifications of Mn (γ, π, and χ phases, respectively). In addition, the temperature sequence of diffusionless γ → π → χ transformations in the cooling process is similar to the temperature sequence of αpolymorphic γ → β → transformations of Mn. In this case, the γ → π transformation has the features of a martensitic analog, and the temperature of the π → χ-transformation of nanosized metastable phases is close to the temperature of the polymorphic β-Mn ⇄ α-Mn transformation. It is shown that the crystal lattices of the π and γ phases obey orientation relationships, for example: (110)π[2 ‾2 1]π║(101)γ[0 ‾1 0]γ.