JOURNAL OF MATERIALS SCIENCE LETTERS 8 (1989) 367-369 Auger electron spectroscopy studies of the thermal stability of amorphous Cos0B20 SALAH-UD-DIN, M. SULEMAN, K. MAHMOOD Centre for Sofid State Physics, University of the Punjab, Lahore 20, Pakistan D. YUANDA Institute for Sofid State Physics, Academia Sin~ca, Hole/, China Controlled heat treatment of metallic glasses, such as a transition-metal refractory-metal boron glass, can produce small amounts of crystallinity which in turn enhances their mechanical properties, for example strength, hardness and ductility [1]. Fine-grain micro- structure consisting of 7-Fe crystallites, produced on heat-treatment of the metallic glasses Fe-B-C-Si, greatly reduced the eddy-current losses at high fre- quencies [2]. In order to fully utilize the crystallization process of metallic glasses, long-term thermal stability tests are regarded as indispensable. These tests involve study of the structural relaxation and crystallization processes of metallic glasses. A number of conven- tional methods are employed for this study. The most commonly used tools are differential scanning cal- orimetry [3], electric resistance measurements [4], dynamic temperature X-ray diffraction [5] and M6ss- bauer spectroscopy [6]. Use has also been made of scanning electron microscopy and transmission elec- tron microscopy [7]. These techniques have their own advantages but none of them can reveal structural changes in the microstructure and chemical composition during the heat treatment. Auger electron spectroscopy (AES) is the best tool for the in situ study of the chemical composition of a surface layer with high sensitivity during the heat treatment. In this communication we report the surface composition of amorphous Co80 B20 during dynamic heating using AES. Amorphous Co80B20 ribbons were supplied by the Institut ffir Werkstoffe der Electrotechnik, Ruhr- Universitfit, Bochum (FRG). A slight surface polish- ing was done with emery paper (1200 grade) followed "0 ",OMv V L f L i i lOO 200 i 1 I 300 400 E (eV) I COLMM J i t ~ i J i 500 600 700 800 Figure l Auger spectrum of amorphous Co~oB=o, by ultrasonic cleaning. The samples were mounted on the heating stage of the Auger electron microprobe (Jeol JAMP 10-S). The specimen surface was sputtered with Ar + ions before starting the heat treatment. The samples were heated to a maximum temperature of 900 K at the rate of 15 K rain -1, in a vacuum of the order of 10 -8 torr. The specimen was held at a given temperature for at least 30 rain before taking an Auger spectrum. Differential thermal analysis (DTA) and thermo- gravimetric analysis (TGA) were carried out with the Netzch Simultaneous Thermal Analyzer STA 429. Calcined alumina (purity 4N) was used as a reference material. The heating rate was kept at 10 K min -~ up to 900 K, The Auger spectrum of a specimen before heating is shown in Fig, 1. No significant impurities are notice- able in the spectrum except oxygen and carbon. Fig. 2 shows the Auger spectra obtained at different tem- peratures during dynamic heating. Peak heights of cobalt at 53 eV and boron at 180 eV were measured in tu "o (a) 2 (b) ) (d) i , i i i o 1;o 2;o 30o 4oo o E (eV) "o (e) 00 (f) (g) (h) 100 200 300 400 E" (eV) F&,ure 2 Auger spectraduring dynamicheating: (a) 525 K, (b) 575 K, (c) 625 K. (d) 675 K, (e) 725 K, (f) 775 K, (g) 825 K, (h) 900 K. 0261-8028/89 $03.00 + .12 © 1989 Chapman and Hall Ltd. 367