Abstract
Aluminium alloy powder having a nominal composition of Al 93 Fe 3 Cr 2 Ti 2 (at%) has been prepared using gas atomisation. The atomised powder present a microstructure of an aluminium matrix reinforced with a spherical quasicrystalline icosahedral phase, in the range of nanometre in size. The powder was consolidated into bars using warm extrusion. The microstructure of the extruded bars retains the quasicrystalline microstructure and the bars present outstanding mechanical properties, i.e. proof stress of 280 MPa at 300 °C. Upon heating the microstructure evolves towards the equilibrium. The thermal evolution was investigated by means of x-ray diffraction, differential scanning calorimeter, scanning electron microscopy and transmission electron microscopy. According to these observations a transformation in two steps is proposed. A first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases.
Highlights
Nano-size quasicrystalline structures have been a subject of interest over recent years due to their potential use as reinforcement in advanced engineering alloys (Kimura et al, 2000)
Nanoquasicrystalline Al93Fe3Cr2Ti2 powder was obtained by gas atomisation, the powder was sieved into well defined size fractions and consolidated into bars by warm extrusion
Quasicrystalline Al93Fe3Cr2Ti2 alloys microscopy (Fig. 4) show the copious presence of near spherical precipitates into the Al matrix. As it was shown in previous work (Todd et al, 2004), x-ray diffraction patterns of the powder showed mainly signal of the α-Al phase together with peaks indexed as an icosahedral phase, i-phase, by using the indexation scheme for icosahedral quasiperiodic crystals (Bancel et al, 1985)
Summary
Nano-size quasicrystalline structures have been a subject of interest over recent years due to their potential use as reinforcement in advanced engineering alloys (Kimura et al, 2000). The stability and the evolution of bulk Al93Fe3Cr2Ti2 extruded bars upon thermal treatments is studied as a function of initial gas atomised powder particle size range, and of the solidification rate.
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