Crystallization kinetics of Al95-x-yMmxNi5(Co,Fe)y series (x = 4, 5; y = 2, 3)

Javier S. Blazquez ,  Hristo Dimitrov ,  Jerzy Latuch ,  Tadeusz Kulik 

Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland

Abstract

Effect of small changes of the composition on the crystallization process of a quaternary AlMmNi(Co,Fe) alloy series (Mm = mischmetal) obtained in amorphous state by melt-spinning technique, is studied using differential scanning calorimetry (DSC) and X-ray diffractrometry (XRD). Devitrification process takes place in several steps for all the studied alloys. Nanocrystalline microstructure appears during the first transformation stage detected by DSC. This microstructure has been characterized by XRD as nanocrystals of α-Al phase embedded in an amorphous matrix. Average grain size, D is about 15-20 nm (estimated using Scherrer formula) and crystalline volume fraction, XC = 50-80 %. The highest XC was found for the lowest Mm containing alloy. Annealing above the second and third transformation stages produces fully crystallized samples. At this stage only equilibrium phases were detected: α-Al, orthorombic Al11Mm3 and orthorombic Al3Ni. Kinetics of nanocrystallization was studied in terms of non-isothermal approaches (Kissinger, Augis-Bennet, Gao-Wang and Ozawa methods). Activation energy of nanocrystallization, Ea ranges from 1,5 to 2,7 eV. The highest values were found for the alloys with the lowest Al content. Combining Gao-Wang and Ozawa methods, an idea of the value of Avrami expoinent, n, at the early (Gao-Wang) and final (constant value in Ozawa) stages of nanocrystallization is obtained: n decreases from 1-1.5 to 0.5.

 

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium G, by Hristo Dimitrov
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-27 17:27
Revised:   2009-06-08 12:55