Journal of Alloys and Compounds 381 (2004) 66–71 Evolution of amorphous and nanocrystalline phases in mechanically alloyed Mg 1.9 M 0.1 Ni (M = Ti, Zr , V) P. Solsona a , S. Doppiu a , T. Spassov b,∗ , S. Suriñach a , M.D. Baró a a Departament de F´ ısica, Facultat de Ciencies, Universitat Autonoma de Barcelona, LMT, Edifici Cc, 08193 Bellaterra, Spain b Department of Chemistry, University of Sofia “St.Kl.Ohridski”, 1 J. Bourchier str., 1126 Sofia, Bulgaria Received 5 February 2004; accepted 25 February 2004 Abstract The evolution of amorphous and nanocrystalline phases in mechanically alloyed Mg 1.9 M 0.1 Ni (M = Ti, Zr, V) was studied under different milling conditions by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis. It was found that the presence of air (oxygen and nitrogen) accelerates the nanocrystallization reaction, but has no influence on the amorphous phase formation during ball milling. The mechanochemical work necessary to obtain a certain degree of amorphization or nanocrystallization in the Mg 2 Ni-based alloys was determined and it was found to control the end product of milling. © 2004 Elsevier B.V. All rights reserved. Keywords: Mg–Ni alloys; Mechanical alloying; Microstructure; Amorphous and nanocrystalline phases; Thermal stability 1. Introduction It is already well known that during high energy ball milling (BM) or mechanical alloying (MA) of Mg–Ni alloys an amorphous phase forms, which nanocrystallizes during subsequent milling [1–4]. It is also established that the mi- crostructure of the Mg alloys has a strong influence on their hydrogen storage characteristics [1–8]. Our recent studies [4,9] were devoted to the preparation of nanocrystalline Mg 2 Ni-based alloys (less than 10 nm in size) by ball milling and by BM with subsequent annealing. The minimum time of milling for reaching nearly 100% of transformation in Mg 2 Ni during mechanical alloying with subsequent low temperature (e.g. 300 ◦ C, 1 h) annealing was determined at different milling intensities. An interesting result of the previous investigation [4] was the difference in the maximum amount of the amor- phous phase formed at two (different) frequencies of the mill at the same ball/powder mass ratio (B/P). Whereas at the lower rotation velocity (400 rpm) about 90% of amor- phicity was reached before the nanocrystallization to start, at 480 rpm the maximum amorphicity obtained was about 65%. ∗ Corresponding author. E-mail address: tspassov@chem.uni-sofia.bg (T. Spassov). It was shown that the samples containing a disordered phase after milling form coarser grained nanocrystalline Mg 2 Ni (10–15 nm) during subsequent annealing than the alloy pre- pared by long-time milling only (<10 nm). Being a continuation of a previous study, the aim of the present work is to follow quantitatively the formation and evolution of the amorphous phase and its further nanocrys- tallization during continuous milling of Mg 1.9 M 0.1 Ni at dif- ferent milling conditions (rpm, B/P mass ratio, gas atmo- sphere, etc.) in order to determine the parameters having the strongest influence on both transformation processes. 2. Experimental Pure elemental powders of magnesium, nickel, titanium, zirconium and vanadium were used as starting materials. The ball milling was performed with planetary mills (Fritsch P5 and P7) with different frequencies and ball to powder (B/P) mass ratio. Handling procedures were performed in a glove box under argon atmosphere. Modified vials were used in order to allow milling under different gas atmo- sphere at controlled pressure. The vials and the balls were made from stainless steel. Small amount of the powder was taken from the mill at regular periods of time for structural, morphological and thermal analysis. 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.02.047