Elsevier

Scripta Materialia

Volume 45, Issue 10, 19 November 2001, Pages 1191-1196
Scripta Materialia

Development of amorphous Al65Cu35−xTix alloys by mechanical alloying

https://doi.org/10.1016/S1359-6462(01)01149-6Get rights and content

Introduction

Development of high-specific strength structural material is always of great importance to the transportation and aviation industry. It is predicted that the strength of light weight aluminium alloys could be significantly enhanced from about 500–600 MPa in age hardened condition to 1200–1550 MPa level in rapidly quenched glassy/amorphous or nanocrystal dispersed glassy/amorphous matrix aluminium based alloys [1]. In the recent times, mechanical alloying has emerged as a convenient solid state synthesis alternative to melt spinning and similar rapid quenching techniques to develop the metallic glasses [2], [3], [4]. Furthermore, carefully designed milling routine and/or subsequent heat treatment may enable dispersion of nanocrystalline intermetallic phases in the mechanically alloyed amorphous/glassy matrix precursor [5], [6]. Recently, we have demonstrated for the first time that mechanical alloying of the Al65Cu35−xTix ternary system within a close composition range yields completely or partially amorphous alloy [7]. However, the phase identity and evolution during milling and/or subsequent annealing in this system have not been determined. In the present paper, we shall report the phase evolution sequence during mechanical alloying and subsequent isothermal annealing (at 773 K) of the selected alloys in the Al65Cu35−xTix ternary system. In addition, we shall also identify an appropriate composition that can yield a completely amorphous microstructure by mechanical alloying.

Section snippets

Experimental

Blends of elemental (>99.5 wt.% purity) Al, Cu, and Ti powders (∼50–100 μm particle size) having the nominal compositions (in at.%) of Al65Cu35−xTix (x=5, 10, 15, 20, 25 and 30 at.%) were ball milled in a Fritsch Pulverisette 5 planetary ball mill at 300 rpm and ball to powder weight ratio of 10:1 using WC vial and balls (10 mm diameter) in stages with up to a cumulative milling time of 40 h. The initial composition of the powder blend varied in the range x=5–30 (at.% Ti) to determine the solid

Mechanical alloying

Fig. 1 reveals the XRD patterns obtained from the Al65Cu20Ti15 samples subjected to mechanical alloying for different lengths of milling time. It is apparent that the intensities of the peaks due to the elemental constituents (Al, Cu and Ti) are considerably reduced by 6 h of milling with simultaneous evolution of additional peaks which may be indexed as the disordered Cu9Al4 phase having a bcc Bravais lattice [9]. In addition to decreasing the intensity, continued ball milling seems to induce

Conclusion

Mechanical alloying of Al65Cu35−xTix (10<Ti<25 at.%) by planetary ball milling up to 30 h leads to the formation of a single phase amorphous or nanocrystalline product. Controlled milling up to (or arresting the milling at) the appropriate stage may develop an in situ composite microstructure comprising amorphous (to a varying degree) and nanocrystalline metallic/intermetallic phases. Ti plays a crucial role in solid state amorphization of Al65Cu20Ti15. Subsequent isothermal annealing of the

Acknowledgements

Useful discussions with Prof. Dr. H.-J. Fecht and Dr. J. Eckert about the results presented in this work are gratefully acknowledged. Partial financial support from the Department of Science and Technology, New Delhi (grant no.: III.4 (23) 92-ET and SP/S2/K-17/98 dt. 29.1.99) is thankfully acknowledged.

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