Bcc metastable phase coexisting with the icosahedral phase in rapidly quenchedFe28Ti68Si4alloys

Abstract

The FeTi-Si quasicrystalline system has been investigated by systematically varying the alloy composition. A metastable bcc phase with the lattice parameter close to 1.31 nm is reported for the ${\mathrm{Fe}}_{28}$${\mathrm{Ti}}_{68}$${\mathrm{Si}}_{4}$ alloy. Its orientational relationship with the icosahedral phase has been established based on x-ray-diffraction and electron-microscopy experiments. Electron-microscopy studies have revealed the interrelationship between the icosahedral and the cubic variants; the twofold, threefold, and fivefold icosahedral (i) phase axes are parallel to 〈001〉, 〈111〉, and nearly 〈530〉 directions of the cubic phase. A possible growth mechanism for the formation of both the icosahedral and the metastable bcc phase has been suggested. Structural transformations originating because of annealing (at 700 and 900 \ifmmode^\circ\else\textdegree\fi{}C) in an argon atmosphere have been investigated. The transformation sequence has been found to correspond to (${\mathrm{FeTi}}_{2}$)(i)long-${>}^{700}$ \ifmmode^\circ\else\textdegree\fi{}C (${\mathrm{FeTi}}_{2}$)(bcc,metastable)long-${>}^{900}$ \ifmmode^\circ\else\textdegree\fi{}C(${\mathrm{FeTi}}_{2}$)(fcc,equilibrium)+\ensuremath{\beta}-Ti.