Mapping Residual Stress Distributions at the Micron Scale in Amorphous Materials
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BULK metallic glasses (BMGs) are attractive materials for high-performance applications in a wide variety of fields.[3,4] This is because their microstructures give rise to, among other things, strengths approaching theoretical limits, high hardness,[5] good fatigue strengths,[6] a uniquely high capacity for elastic energy storage per unit volume, low damping, and remarkable fracture toughness, which distinguish them from other engineering materials.[7] However, thermal residual stresses are an unavoidable issue[8] due to the fast cooling rates needed to retain a glassy structure on cooling. Furthermore, these residual stresses have been shown to have significant effects on their mechanical behavior.[9–11] Consequently, an accurate means of assessing residual [1,2]
BARTLOMIEJ WINIARSKI, Postdoctoral Research Associate, and PHILIP J. WITHERS, Professor, are with the School of Materials, The University of Manchester, Grosvenor St, Manchester, M1 7HS, United Kingdom. Contact e-mail: [email protected] RICHARD M. LANGFORD, formerly Senior Experimental Officer, with the School of Materials, The University of Manchester, is Facility Manager, Electron Microscopy Suite, The Canvendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, United Kingdom. JIAWAN TIAN, Postdoctoral Scholar, and PETER K. LIAW, Professor and Ivan Racheff Chair of Excellence, are with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. YOSHIHIKO YOKOYAMA, Associate Professor, is with the Materials Science and Engineering Department, Himeji Institute of Technology, Shosha 2167, Himeji, Japan. This article is based on a presentation given in the symposium ‘‘Bulk Metallic Glasses VI,’’ which occurred during the TMS Annual Meeting, February 15–19, 2009, in San Francisco, CA, under the auspices of TMS, the TMS Structural Materials Division, TMS/ASM: Mechanical Behavior of Materials Committee. Article published online December 12, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
stresses is essential not only for understanding how they affect the mechanical behavior of BMGs, but also to guide the tailoring of residual stress levels through subsequent processing treatments such as shot peening.[9] Unfortunately, stresses in amorphous materials cannot easily be determined at the micron scale by conventional laboratory methods, either by destructive methods (too coarse), or conventional X-ray diffraction analyses (amorphous). As a result, stress measurements in metallic glasses in general and those relating to peening, in particular, are sparse.[12] Residual stresses are those stresses that are retained within a material when no external forces are acting. Depending on their sign, magnitude, spatial distribution, and the scale over which they equilibrate, residual stresses can alter the component performance and promote/ inhibit failure processes.[13] As stated earlier, quench stresses are an inevitable outcome of metallic glass production, while thermal tempering is regularly used to intr
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