Stability and decomposition mechanisms of supersaturated solid solutions in rapidly solidified aluminium–transition metal alloys

Abstract

The annealing of supersaturated solid solutions has been studied in a number of rapidly solidified AI-transition metal alloys using transmission electron microscopy. Two very different decomposition processes have been found. The first involves the generation and migration of dislocation networks which provide short circuit diffusion paths to the grain boundaries for the solute atoms, where they precipitate as the equilibrium phase. Typical examples are Al–Mo and Al–V The second mechanism involves the precipitation of metastable quasicrystals in the grains before the equilibrium phase is formed, also within the grains. This process has been observed in Al–Cr and Al–Fe alloys. The different mechanisms are discussed in terms of the ability to generate dislocations and the stability of quasicrystal precipitates in Al–transition metal alloys. Stable supersaturated solid solutions containing quasicrystals exhibit strong strengthening behaviour. The significance of these observations is discussed in terms of the development of advanced Al alloys for high performance applications.MST/3356