Mechanism of mechanical alloying in NiAl and CuZn systems

TLDR: In this paper, the NiAl and Ni 3 Al phases were synthesized by mechanical alloying of elemental blends in a planetary mill, and two different modes of alloying were identified.

Abstract: Nanocrystalline Al 3 Ni, NiAl and Ni 3 Al phases in the Ni Al system and the α, β, γ and e phases in the Cu Zn system were synthesized by mechanical alloying of elemental blends in a planetary mill. In the as-milled state, Al 3 Ni and AlNi were always ordered, while Ni 3 Al was disordered. MA results in a large extension of the NiAl and Ni 3 Al phase fields particularly towards Al-rich compositions. The crystallite size was finest ( ∼ 6 nm) when NiAl and Ni 3 Al phases coexist after prolonged milling. In contrast, in all Cu Zn blends containing 15–85 at.% Zn, the Zn-rich phases were first to form and final crystallite sizes were coarser (15–80 nm). Two different modes of alloying have been identified. In the case of NiAl and Al 3 Ni, where the ball milled product is ordered and the heat of formation is large ( ΔH f > 120 kJ mol −1 ), a rapid discontinuous mode of alloying accompanied with an additive increase in crystallite size is detected. In all other cases irrespective of the magnitude of ΔH f , gradual diffusive mode of intermixing during milling seems to be the underlying mechanism of alloying.