Some correlations for diffusion in amorphous alloys
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Kuldeep and Animesh K. Jain Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay^fOO 085, India (Received 7 September 1988; accepted 25 January 1989) Diffusion of several impurity atoms (Cu, Al, Au, and Sb) has been studied in Zr61Ni39 and Fe82B18 amorphous alloys. A definite correlation between the diffusion coefficient (D) and the atomic size of the diffusant is seen for the metal-metal (M-M) alloy, while it is not clear for the metal-metalloid (M-Me) alloy. Based on the present data, as well as other published data in binary amorphous alloys, empirical correlations have been found between (i) the activation energy ( 0 and the energy required to form a hole of the size of the diffusing atom in the host alloy, and (ii) the pre-exponential factor (Do) and Q. While the former correlation is seen only for binary M-M type of amorphous alloys, the latter correlation is more general and holds for all types of amorphous alloys. Based on the correlation between Do and Q, it is proposed that there are two distinct mechanisms of diffusion in amorphous alloys.
I. INTRODUCTION Since the publication of the first paper1 on diffusion in amorphous alloys, quite a few measurements have been reported and reviewed in the literature.2"5 However, there are very few investigations where a systematic study of various diffusants in an amorphous alloy has been done.6"8 Such studies are useful for understanding the mechanism of diffusion in these alloys and for finding out suitable empirical correlations, as has been done for crystalline systems.9"14 In this paper, we report some empirical correlations for diffusion in amorphous alloys obtained from a systematic study15 of diffusion of various impurity atoms (Cu, Al, Au, and Sb) in binary metal-metal (Zr61Ni39) and metalmetalloid (Fe82B18) amorphous alloys. Based on the results of these investigations, some correlations have been obtained between (i) D and the radius (r) of the diffusing atom, (ii) the activation energy ( 0 for diffusion and the energy AZ/^B required to form a hole of the size of the diffusing atom i in the host alloy A^B^., and (iii) the preexponential factor (Do) and the activation energy ( 0 . II. EXPERIMENTAL The amorphous alloys, having compositions of Zr61Ni39 and Fe82B18, were produced by the melt-spinning technique. These alloys exhibited crystallization temperatures (Tx) of 741 K and 726 K, respectively, in a differential scanning calorimeter at a heating rate of 20 K/min. The diffusion rates (D) of Cu and Al were measured by Auger Electron Spectroscopy (AES), and those of Au and Sb were measured by Rutherford Backscattering Spectrometry (RBS).15"17 The Auger analysis was performed in an electron spectrometer (PHI model 551) using a 3.0 KeV primary electron beam in conjunction with 1.0 KeV Ar + beam for etching the surface. The RBS analysis was carried out with a 2.0 MeV beam of J. Mater. Res., Vol. 4, No. 3, May/Jun 1989
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He+ ions obtained from the 5.5 MV Van de Graaff accelerator at BARC, Bombay
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