Characterization of dispersed intermetallic Phases in Rapidly Quenched Al-Ti-Ce Alloys

Abstract

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly so- lidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure (α _o = 1.44 ± 0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence sug- gests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C.