The effect of MgNi2 intermetallic compound on nanostructurization and amorphization of Mg-Ni alloys processed by controlled mechanical milling

Two Mg-Ni alloys with 27.9+/-11.1 and 57.5+/-0.8 at% Ni, fabricated by ingot metallurgy (IM) and containing similar to9 and similar to79 vol% of the MgNi2 phase. respectively. were ball (mechanically) milled in a magnetic Uni-Ball-Mill 5 under controlled shearing mode for 10, 30, 70 and 100 h. The evolution of the microstructure of milled powders is presented. It is observed that the Mg2Ni phase undergoes a partial amorphization in the Mg-Ni alloys containing similar to79 vol% of the MgNi2 phase while no amorphization of Mg2Ni is observed in the alloy containing only similar to9 vol% of MgNi2 The results are rationalized in terms of the enthalpy effects based on the application of Miedema's semi-empirical model to the phase changes in ball-milled intermetallics and the critical nanograin size required to be formed in the Mg2Ni phase before triggering its amorphization, which is enhanced by the presence of hard MgNi, phase during ball milling. The milled powders of 27.9+/-11.1 at% Ni alloy, after long-term milling for 100 h, did not absorb hydrogen. (C) 2003 Elsevier Science B.V. All rights reserved.