Microstructural evolution during controlled ball milling of (Mg2Ni+MgNi2) intermetallic alloy

Nearly dual-phase Mg-Ni alloy fabricated by ingot metallurgy (IM) and comprising ∼30 vol% Mg2Ni and ∼61 vol% MgNi2 intermetallic compounds (remaining ∼9 vol% of unreacted Mg) was mechanically (ball) milled under controlled shearing for 10, 30, 70 and 100 h. The majority of the medium- and small-sized powder particles exhibited a relatively homogeneous microstructure of milled Mg2Ni and MgNi2. A fraction of large-sized particles developed the 'core and mantel' microstructure after milling for 70 and 100 h. The 'core' contains poorly milled MgNi2 particles and the 'mantel' is a thoroughly milled mixture of Mg2Ni, MgNi2 and, possibly, residual Mg. X-ray diffraction provides evidence of nanostructurization and eventual amorphization of a fraction of a heavily ball milled Mg2Ni phase. The remnant Mg2Ni developed a nanocrystalline/submicrocrystalline structure. The co-existing MgNi2 phase developed a submicrocrystalline structure within the powder particles. The results are rationalized in terms of enthalpy effects by the application of Miedema's semi-empirical model to the phase changes in ball milled intermetallics