Materials Science and Engineering A 375–377 (2004) 776–780 Influence of the wheel speed on the thermal behaviour of Cu 60 Zr 20 Ti 20 alloys Á. Révész a,c , A. Concustell a , L.K. Varga b , S. Suriñach a , M.D. Baró a,∗ a Department of Physics, Faculty of Sciences, Universitat Autònoma Barcelona, Edifici Cc, 08193 Bellaterra, Barcelona, Spain b Research Institute for Solid state Physics and Optics, Hungarian Academy of Sciences, H-1525 Budapest, P.O.B. 49, Hungary c Department of General Physics, Eötvös University, H-1518 Budapest, P.O. Box 32, Hungary Abstract The effect of the wheel velocity’s strong influence on the glass forming ability (GFA), the thermal stability and the crystallization kinetics of ductile Cu 60 Zr 20 Ti 20 ribbons has been studied. The samples were characterised by differential scanning calorimetry (DSC) using continuous heating and isothermal annealings, X-ray diffraction and microhardness. The DSC measurements revealed that the higher wheel speed results in a higher glass transition (T g ) and higher crystallization temperature (T on ). Independent of wheel speed, the crystallization takes place in a two-stage process. From the isothermal treatment, the crystallization kinetics was analysed using the Avrami model. The microhardness exhibits a linear relationship as a function of the crystallized volume fraction. A perfect solute mixture model of defect free nanoparticles embedded in an amorphous matrix was used to account for this strengthening mechanism. © 2003 Elsevier B.V. All rights reserved. Keywords: Cu-based glasses; Thermal stability; Nanocrystallization kinetics; Microhardness 1. Introduction The recent discovery that a number of alloys can be pre- pared into amorphous state at cooling rates of 1–100 K/s has generated great interest [1,2] because this enables manufac- turing of amorphous metallic alloys not only in the form of thin ribbons, but also in the form of bulk materials. It has been found that the addition of Ti to the Cu–Zr and Cu–Hf binary systems drastically reduces the melting temperature, which strongly correlates with the glass form- ing ability (GFA) and new Cu-based bulk amorphous alloys were formed in Cu–Zr–Ti and Cu–Hf–Ti ternary systems by copper mold casting method [3]. These alloys exhibit good mechanical properties; however, taking into account that the amorphous state is metastable with respect to the crystalline state, all the physical properties will be affected by structural relaxation and/or crystallization. To extend the application of these alloys as structural bulk metallic glasses, it is nec- essary to determine the influence of thermal treatments on the mechanic properties and to our knowledge, their thermal behaviour is rarely studied in detail. ∗ Corresponding author. Tel.: +34-93-581-1657; fax: +34-93-581-2155. E-mail address: dolors.baro@uab.es (M.D. Bar´ o). In this work, as a preliminary study, we focus on the GFA, crystallization kinetics, microstructure and microhard- ness behaviour of Cu 60 Zr 20 Ti 20 alloys. The influence of the preparation conditions on their thermal and mechanical properties will also be discussed. 2. Experimental 2.1. Sample preparation Ingots were prepared by induction-melting a mixture of pure (99.99 wt.%) Cu, Zr, and Ti. The Cu 60 Zr 20 Ti 20 ribbons (3–4 mm wide and about 20 m thick) were obtained using a single roller melt spinning technique in inert atmosphere with a Cu-wheel rotating at tangential velocities of 39 m/s (ribbon #I) and 59 m/s (ribbon #II). The ribbons were ductile and can be bent 180 ◦ without failure. 2.2. DSC measurements Differential scanning calorimetry (DSC) experiments were carried out in a Perkin-Elmer DSC-7 under a pure dynamic argon atmosphere. Continuous heating studies were performed at scan rates in the range of 2.5–80 K/min. Isothermal heat treatments were carried out by heating 0921-5093/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2003.10.151