Indentation creep of a Ti-based metallic glass
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Y.L. Chiua) Department of Chemical and Materials Engineering, University of Auckland, Auckland 1142, New Zealand; and Department of Metallurgy and Materials, University of Birmingham, Edgbaston B15 2TT, United Kingdom
J. Shenb) School of Materials Science and Engineering and Micro/Nano Technology Research Center, Harbin Institute of Technology, Harbin 150001, China
J.J.J. Chen Department of Chemical and Materials Engineering, University of Auckland, Auckland 1142, New Zealand
J.F. Sun School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China (Received 30 July 2008; accepted 31 October 2008)
In this work, the time-dependent plastic deformation behavior of Ti40Zr25Ni3Cu12Be20 bulk and ribbon metallic glass alloys was investigated using a nanoindentation technique at room temperature with the applied load ranging from 5 to 100 mN. The stress exponent n, defined as e_ ¼ Asn , has been derived as a measure of the creep resistance. It was found that the measured stress exponent increases rapidly with increasing indentation size, exhibiting a positive size effect. The size effect on the stress exponent n obtained from the bulk sample is more pronounced than that obtained from the ribbon sample. The deformation mechanism involved will be discussed. I. INTRODUCTION
Due to the high-strength, high elastic limit and excellent corrosion resistance, bulk metallic glasses (BMGs) have attracted increasing interest in the research community.1–3 However, BMGs often have limited plasticity when deformed at temperatures below their glass transition temperatures.4,5 Depth-sensing nanoindentation is an ideal technique to probe the mechanical properties of glassy alloys from a small volume.6–8 During indentation, the applied load can be controlled at a constant value, whereas the penetration of the indenter tip into the sample surface is continuously recorded. This is often called the constant-load indentation creep test, and it has been widely used to study the time-dependent plasticity (creep) of crystalline materials.9–12 The stress exponent, n, of steady-state creep can be derived from the constantload indentation tests.9,10,13,14 However, nanoindentation creep studies of glassy alloys are rare.15–17
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2009.0119 J. Mater. Res., Vol. 24, No. 3, Mar 2009
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In this work, the time-dependent deformation behavior of Ti-based metallic glass has been studied using the nanoindentation technique. Our experiments have shown a size effect on the stress exponent n, and this effect is more significant on the ribbon sample, and the stress exponent measured from the bulk metallic glass sample is larger than that measured from the ribbon sample. II. EXPERIMENTAL PROCEDURE
Alloy ingots with nominal composition of Ti40Zr25 Ni3Cu12Be20 (at.%) were prepared by arc melting a mixture of pure elements in a Ti-gettered argon atmosphere. Bulk
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