Microstructure evolution in CuZrAl alloys during ball-milling K. Tomolya 1* , D. Janovszky 1 , M. Benke 2 , A. Sycheva 1 , M. Sveda 1 , T. Ferenczi 2 , P. Pekker 1 , I. Cora 1 , A. Roósz 1 1 MTA-ME Materials Science Research Group, Miskolc-Egyetemvaros H-3515, Hungary 2 University of Miskolc, H-3515 Miskolc-Egyetemvaros, Hungary *corresponding author: femkinga@uni-miskolc.hu Abstract: The microstructure evolution during mechanical milling was studied in the CuZrAl system. The compositions lay on the two liquidus surfaces indicating different solidification processes in the three alloys. Cu(55-x)Zr(35+x)Al10 (x = 0; 5; 10 at%) master alloys were produced by arc melting. After identification of the phases, the master alloys were milled for 25 hours and amorphous/crystalline powders were synthesized. The master alloys contained Al21Cu28Zr51, AlCu2Zr, CuZr and traces of Cu10Zr7 phases in different volume fractions. The optimal milling time was determined to be 15 hours based on the results of X-ray diffractometry (XRD) and differential scanning calorimetry (DSC) examinations. The 5 h milled powder contained CuZr and Al21Cu28Zr51 phases, which diminished due to further milling resulting in amorphous matrix composite with nanosized Al21Cu28Zr51 phase. The thermal stability of the samples was investigated by DSC. The peak temperatures of the first crystallization process of the as-milled powders shifted as function of milling time and polynomial curves were fitted to the measured points. Keywords: CuZrAl alloys, amorphous/nanocrystalline composite, ball-milling, powders 1. Introduction Cu-Zr based bulk metallic glasses (BMGs) attracted high attention because of their relatively low costs [1-3]. Aluminum has been regarded as useful element to improve the plasticity of the CuZr-based BMGs [4]. The addition of minor Al quantities (up to 10 at%) to the Cu–Zr glassy alloys may improve their thermal stability, mechanical properties and glass forming ability (GFA) [5, 6]. Glassy alloys can be produced by casting and by solid state techniques such as mechanical alloying (MA) [7-10, 12] or mechanical milling (MM) [8, 11-13]. Both solid state techniques have now been shown to be capable of synthesizing a variety of equilibrium and non- equilibrium alloy phases starting from blended elemental or prealloyed powders. Additionally, powders can be mechanically activated to cause chemical reactions at near to room temperature, which is normally required to produce pure metals, nanocomposites, and a variety of commercially useful materials. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. The advantage of MM over MA is that only reduction in particle size and transformation in the structure need to be induced mechanically since the powders are already alloyed, so the time required for processing is short. During milling, the effect of transmitted mechanical energy causes the formation of amorphous structure in the initial, crystalline powders. In a planetary ball-mill, both the vials and the support disk rotate around their own axes. Due to the centrifugal force produced by these rotations, the grinding balls impact to each other and to the wall of the vial while some amount of powder is trapped in between them [9]. Coalescence and fragmentation of the particles keep balance, because of the high mechanical stress effects caused by the balls. Repeated mechanical mixing, cold welding and fracturing take place and cause the formation of a fine powder with a changed