Microstructure investigation of rapidly solidified Al-V-Fe alloys
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hek and Joseph K.L. Lai Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Hong Kong, People’s Republic of China
Z. Bian, X.D. Hui, and G.L. Chen State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, 100083 Beijing, People’s Republic of China (Received 6 June 2001; accepted 24 January 2002)
The microstructures and their thermal behaviors of quenched Al94V4Fe2, Al90V8Fe2, Al86V8Fe6, and Al85V9Fe2Ni4 alloys were investigated by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The as-quenched microstructures of the four alloys consist of quasicrystal particles and a fcc-␣–Al matrix. The as-quenched Al86V8Fe6 and Al85V9Fe2Ni4 alloys also contain a small volume fraction of amorphous phase. All phases observed have fine morphologies with grain sizes of less than 100 nm. With the increase in V from 4 to 8 at.% at 2 at.% Fe, the average grain size decreases from 100 to 70 nm and the melting temperature of ␣–Al solid solution increases from 640 to 653 °C. The alloy with 8 at.% V has a finer and more stable microstructure than that of the alloy with 4 at.% V. The Fe addition has minor effect on grain size but improves the glass-forming ability. The Ni addition significantly improves the glass-forming ability and refines the microstructure. The metastable amorphous and quasicrystalline phases transform into a stable crystalline phase during continuous heating and cooling. The stable phases in these Al–V–Fe alloys include ␣–Al(V, Fe), Al10V, and Al80V12.5Fe7.5.
I. INTRODUCTION
Having low density and good mechanical properties, aluminum alloys are among the most important materials for aerospace and automobile applications. Ordinary Albase alloys are strengthened by using conventional mechanisms such as solid solution, precipitation, grain size refinement, dispersion, work hardening, and fiber reinforcement. The tensile fracture strength of conventional Al-base alloys can reach up to about 650 MPa. To design new Al-base alloys with a higher tensile strength, new strengthening mechanisms must be considered, and advanced fabrication methods such as rapidly solidification techniques must be used. In the past few years, phases with nonperiodic structures such as amorphous and quasicrystalline phases with icosahedral structure attracted many research attention in
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J. Mater. Res., Vol. 17, No. 4, Apr 2002 Downloaded: 27 Apr 2015
this field. Some nano-quasicrystalline Al-base alloys, exhibiting a good combination of high tensile strength, high ductility, high fatigue strength, and high elevatedtemperature strength, were discovered in recent years.1,2 The recent literature reported that the tensile strength of melt-spun Al-base alloys can reach up to 1260 MPa by the formation of a homogeneous amorphous structure3 and even up to 1560 MPa by the homogeneous precipitation of nanoscale fcc-␣–Al particl
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