Journal of Solid State Chemistry 154, 145 } 147 (2000) doi:10.1006/jssc.2000.8825, available online at http://www.idealibrary.com on Crystallization Mechanism of Co 77 B 23 Amorphous Alloy M. Ajmal, M. S. Khan, and A. Shamim Centre for Solid State Physics, Punjab University, Lahore, Pakistan Received September 9, 1999; in revised form April 10, 2000; accepted April 30, 2000 Crystallization behavior of Co 77 B 23 alloy at increasing temper- ature has been studied using resistivity measurements and auger- electron spectroscopy. The amorphous nature of the specimen ribbon was ascertained by X-ray di4raction analysis. The resis- tivity measurements showed a gradual increase of resistivity with temperature, which at about 600 K showed an abrupt fall in its value due to the onset of crystallization. As the heating con- tinued, more peaks at di4erent temperatures were detected in the resistivity+temperature distribution curve. These were identi5ed as belonging to other phase changes in the crystallized alloy. Auger-electron analysis has been made to investigate chemical composition changes during heating. The results show a decrease in boron content on surface layers, which points to an inward di4usion of boron atoms. An excess of cobalt atoms is left on the surface, making the amorphous layers on the surface unstable, which leads to crystallization.  2000 Academic Press INTRODUCTION Amorphous metallic alloys or noncrystallized solid meta- ls are formed by rapid cooling of the melt. The glassy alloys based on third-transition metal borides possess an interest- ing combination of electrical, optical, magnetic, and mecha- nical properties due to their unique structure, in particular a lack of magneto-crystalline anisotropy and an absence of dislocation (1). This combination of remarkable properties are directly derived from their glassy state, e.g., soft fer- romagnetism, relatively high electrical resistivity, very high fracture stress, better ductibility, and excellent corrosion behavior (1, 2). It is worth nothing that such a combination of properties is not found in any known crystalline material. Fabrication and casting techniques of amorphous alloys are on the verge of yielding commercially applicable prod- ucts such as wires and ribbons, which can be used as strengthening agents in aerospace composites and as trans- former cores with great advantages. Fabrication of glassy alloys depends entirely on the glass- forming ability criterion, comprising certain rules (1} 4). There are a number of fabrication methods (1}7), but the samples studied in this work were prepared by rapid quenching (10 K/s) from the melt. This is recognized as the most versatile method for fabricating good quality glassy alloys. Glassy metallic alloys lose their superior properties on crystallization. From an application point of view, the knowledge about crystallization temperature of an amorph- ous alloy is essential. A successful method is dynamic tem- perature X-ray di!raction (DTXD), which is a technique in which X-ray di!raction pattern is recorded on a photo- graphic "lm that continuously runs in synchronization with the increasing temperature of the sample. Another useful technique is dynamic temperature resistivity measurement (DTRM) in which the resistivity measurement of the sample is made at an increasing temperature at a constant rate (8 }12). This technique has been used to study the crystalli- zation temperature of Co  B  in this work. Another point of interest is to study the mechanism that leads to crystalli- zation. For this study Auger electron spectroscopy has been used. EXPERIMENTAL TECHNIQUE The amorphous alloy Co  B  was prepared at Ruhr University, Bochum, Germany by rapid quenching of the melt, using the free jet melt spinning technique (1} 3). Metal- lic ribbons about 3 mm wide and 30 m thick were prepared in this way. The amorphous or glassy nature of the ribbon specimen so obtained was ascertained by X-ray di!raction analysis. Such an alloy being in metastable state tends to settle to a stable crystallization state on heating at a certain minimum temperature called crystallization temperature. The dynamic resistivity measurement technique (8, 9) was used to determine the crystallization temperature of the ribbon sample. A 15-cm-long ribbon piece was "xed onto a small and thin unglazed ceramic slab with four thin tungston wire springs along a straight line. The whole as- sembly was put in a Gallenkamp tube furnace and heated at a constant rate of 50 K/h in an inert atmosphere of argon. The four tungston wire springs also served as electrical contacts with the sample, whose resistivity was determined by the potential probe method using the apparatus shown in Fig. 1. 145 0022-4596/00 $35.00 Copyright  2000 by Academic Press All rights of reproduction in any form reserved.