Structure and stability of the precipitates in melt spun ternary Al-transition-metal alloys

Abstract

The decomposition of supersaturated solid solution of ternary, melt spun Al-transition-metal alloys has been examined using analytical transmission electron microscopy. It has been found that the presence of small amounts of iron in AlV, AlMo and AlCr alloys can give rise to a fine dispersion of P-phase precipitate in the grain centres. It has been shown that the P-phase is quasicrystalline phase and has an orientation relationship with Al matrix as: i2|〈001〉 Al, 〈 τ 2 τ1〉 Al, i3|〈111〉 Al, 〈 τ 210〉 Al; i5|〈 τ10〉 Al, τ = (1 + √5)/2. The stability of quasicrystals is significantly improved by the presence of iron in A1-transition-metal alloys. The effect of iron on stabilising the quasicrystal precipitates is believed to be due to the fact that iron replaces the oversized transition metal (TM) atoms V, Cr and Mo in the smaller TM sites, resulting in a reduction of structural stress of quasicrystalline phase. The significance of these observations on the structure and stability of quasicrystal precipitates is discussed in terms of the development of high temperature dispersion strengthening Al-based alloys with transition metals.