JOURNAL OF MATERIALS SCIENCE 24 (1989) 3076-3080 Structure and stability of rapidly quenched AIsoCr14-x Fex alloys D. W. LAWTHER Department of Physics, Da/housie University, Halifax, Nova Scotia, Canada B3H 3J5 R. A. DUNLAP* Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5 and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA D. J. LLOYD Kingston Research and Development Centre A/can International Limited, Kingston, Ontario, Canada K7L 4Z4 M. E. McHENRY Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA The structural and thermal properties of melt spun AI8oCr14_xFe x alloys have been investigated using X-ray diffraction, transmission electron microscopy, electron diffraction and differential thermal analysis. Electron diffraction patterns indicate that all alloys contain quasicrystalline nodules with icosahedral symmetry in a matrix of fcc aluminium. Microscopically the alloys fall into two categories; those with x ~< 6 and those with x > 6. The first class alloys shows large (> 1 #m) icosahedral crystallites with well defined dendritic crystallite growth and sharp quasicrystalline X-ray diffraction peaks. The latter alloys show quasicrystalline crystallites which are predominantly much smaller as well as considerably broadened X-ray diffraction peaks. Thermal analysis measurements indicate that the activation energy for crystallization in these alloys is about 1.5 eV. I. Introduction A quasicrystalline phase exhibiting icosahedral sym- metry has been observed in a number of rapidly solidi- fied alloys. The most commonly studied of these are various aluminium-transition metal alloys [1-3]. While the existence of the icosahedral phase in rapidly solidi- fied alloys of aluminium with early 3d transition metal elements (e.g. vanadium, chromium and manganese) is well established [1, 2, 4-6], there is still some con- troversy concerning the structure of some alloys of aluminium with the late 3d transition metal elements (e.g. iron, cobalt, nickel) [1-4, 7, 8]. A1-Fe alloys near the stoichiometry A16Fe are a case in point. While some authors have reported these alloys to be of the icosahedral structure [3, 8] other measurements seem to indicate that these alloys are of the related decagonal phase [e.g. 10]. In any case it seems to be well established that the X-ray diffraction peaks result- ing from the metastable phase in rapidly quenched A1-Fe (and other aluminium-late 3d transition metal alloys) are considerably broader than those from metastable A1-Mn (and other aluminium-early 3d transition metal alloys) [2, 3]. In the present work we have undertaken an investigation of the structure and stability of the rapidly quenched alloys Al~6CrI4 ,.Fe,. (0 ~< x ~< 14); a series covering the range of com- positions from A186Cq4, a well established icosahedral alloy with sharp X-ray diffraction peaks to A186FeI4 a questionable icosahedral alloy with broad diffraction peaks. 2. Experimental methods Alloys were prepared by first arc melting high purity elements under an atmosphere of argon. Rapidly solidified ribbons were prepared by ejecting melts from a 0.7 mm orifice using a 100 kPa over pressure of argon onto the surface of a single copper roller. The surface velocity of the roller was approximately 65 m sec ~ and all ribbons were quenched into air. X-ray diffraction patterns of all as-quenched rib- bons were obtained on either a Siemens powder diffractometer or a Rigaku RU300 rotating anode diffractometer using CuK~ radiation. Differential thermal analysis (DTA) measurements were performed on a Fisher 260F thermal analyser (see reference [11] for further details). All alloys pre- pared in this work were tested using a heating rate of 20 K rain ~. A186Cr14and Al~0FeL4were further treated at various heating rates to determine the activation energy for crystallization. These data were analysed *Present address: Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5. 3076 0022-2461/89 $03.00 + .12 © 1989 Chapman and Hall Ltd.