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Ball milling of Al-based alloys to obtain amorphous-nanocrystalline structure

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Considering a high strength to weight ratio of Al-based alloys as well as outstanding properties of metallic materials in a glassy state, amorphous aluminum alloys have attracted considerable attention due to their potential in structural applications for transportation and aviation industry[1÷8]. Metastable phases in amorphous or quasicrystalline state can induce two to three times higher strength as compared with those processed through precipitation/age-hardening in crystalline Al‑alloys [1, 2]. The first formation of amorphous single phase in Al‑based alloys containing more than 50 at. % Al was found in 1981 for Al-Fe-B and Al-Co-B ternary alloys [1], but they were very brittle and hence have not attracted much attention. Since then, glass forming ability has been determined in a number of Al-based alloys consisting of Al + transition metal + rare-earth elements, processed mainly by rapid solidification or gas atomization methods [8]. It has been also found that ductility in aluminum alloys can be improved when a few nanometer size crystals are embedded in the amorphous matrix [7]. Choi et al. [9] reported tensile fracture strength as large as 1980 MPa for an amorphous alloy containing about 18% Al nanocrystals - this strength was nearly 1.6 times higher than for the fully amorphous alloy. Later, Kawamura et al. [3] attained a bulk compressive strength of 1420 MPa by hot compaction of gas-atomized amorphous Al85Ni5Y8Co2 powder with nanocrystalline dispersed amorphous matrix. Among many techniques of synthesizing novel materials including nanocrystalline or amorphous products there are melt spinning, gas atomization and similar rapid quenching methods [2] but mechanical alloying (MA) by high-energy ball milling is a convenient solid state synthesis alternative for them. It gives the opportunity of obtaining various phases in the material without need to melt pure elements of the alloy. Furthermore, in the one pro[...]

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