Phase transformations in Al₇₀Ni₂₄Fe₆ decagonal system during high energy ball milling

Abstract

In the present investigation, the decagonal phase in Al₇₀Ni₂₄Fe₆ alloy was used for studying the structural and microstructural stability during ball milling in an attritor mill for 1, 2, 4, 8, and 12 h under hexane medium with a powder to ball ratio of 1:100. The milled powder was annealed in an argon atmosphere for durations ranging from 1 to 40 h at 500°C. The as-cast alloy was found to consist of micron size decagonal phase as a major one along with minor amount of Al₃Ni and Al₁₃(Fe,Ni)₄ crystalline phases. Powders milled for more than 8h contained predominantly the B2 phase. The crystallite size of the B2 phase was estimated to be around 17 nm after 12 h of milling. A lamellar like microstructure exhibiting the presence of nano-phase embedded in the grain of B2 phase has been found to evolve after 8 h of ball milling. Subsequent annealing treatment at 500°C for 10, 20 and 40 h of mechanically milled powder for 12 h has led to the transformation of B2 phase to the τ₃ type vacancy ordered phase. The implications of these phase transformations and the evolution of corresponding microstructures will be discussed.

Acknowledgements

The authors would like to thank Prof. S. Ranganathan, Prof. S. Lele and Prof. B.S. Murty for many stimulating discussions. The financial support from the Ministry of Non-Conventional Energy Sources (MNES) and DST New Delhi, India is gratefully acknowledged. The author (NKM) would like to thank Alexander von Humboldt Foundation for Research Fellowship during which a part of the work was completed. Another author (TPY) acknowledges the support of CSIR for award of Senior Research Fellowship.