Surface microstructure of Zr 41.25 Ti 13.75 Cu 12.5 Ni 10.0 Be 22.5 , a bulk metallic glass
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Surface microstructure of Zr41.25 Ti13.75 Cu12.5 Ni10.0 Be22.5 , a bulk metallic glass M. A. LaMadrid Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91109
S. D. O’Connor Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91109
A. Peker and W. L. Johnson Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91109
J. D. Baldeschwieler Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91109 (Received 16 June 1995; accepted 14 February 1996)
The surface of Zr41.25 Ti13.75 Cu12.5 Ni10.0 Be22.5 , a bulk metallic glass prepared by RF induction melting, has been imaged using atomic force microscopy. The untreated surfaces were very smooth; features were no higher than 3 nm over a 10 3 10 mm region, comparable to many polished surfaces. Two types of microstructure were also observed; periodic striations forming either a striped or a checkered structure were present, with wavelengths between 1 and 2 mm, and amplitude of approximately 2 nm; in other cases, “cracked mud”-like patterns were observed. These microstructures could be related to strain-induced surface roughening; preliminary calculations are presented that are consistent with this hypothesis.
I. INTRODUCTION
Recently, Peker and Johnson discovered a class of easily processible metallic glasses.1 These glasses require cooling rates of 10 Kys or less, orders of magnitude slower than traditional metallic glasses, and can be heated well above the glass transition temperature without crystallization. Metallic glasses possess many technologically useful properties, including high strength/weight ratio, high wear resistance, low frictional coefficient, and high corrosion resistance. Previous metallic glasses require cooling rates of 106 Kys or more, producing only thin films or foils, limiting their application. These other types of glasses also crystallize below the glass transition temperature (Tg ). These new metallic glasses can be manufactured with dimensions thicker than an inch and processed above Tg . These properties increase substantially the usefulness of metallic glasses. The correlation among surface topography, surface chemistry, and friction in these metallic glasses is under investigation in our laboratory. This report presents the topographic results obtained using atomic force microscopy. Three types of surface structures have been observed: (i) Disordered regions with roughness smaller than 3 nm. (ii) Periodic stripes and checkered patterns 1494
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 6, Jun 1996
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with wavelengths between 1 and 3 mm and amplitudes between 2 and 3 nm. (iii) Regions that appear as cracked mud-like patterns. II. EXPERIMENTAL DETAILS
The samples were bulk metallic glass (BMG) ingots of Zr41.25 Ti13.75 Cu12.5 Ni10.0 Be22.5 , ranging in si
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