Identifying Deformation and Strain Hardening Behaviors of Nanoscale Metallic Multilayers Through Nano-wear Testing
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WEAR is defined as the deformation and material loss due to sliding contact.[1] It is often cited as an issue in a variety of applications, including manufacturing,[2,3] aerospace,[4] and orthopaedic[5] systems among others. Tribology, or the study of wear, friction, and lubrication,[6] is a complex problem and does not depend solely on initial hardness.[1] The wear behavior of a system also varies as a function of applied load,[7,8] sliding velocity,[8,9] and elastic properties.[9,10] For this reason, wear response must be determined in addition to studies of static mechanical behavior. Additionally, the tribological test should be designed to mimic the conditions that D. ROSS ECONOMY and B.M. SCHULTZ, Research Students, are with the Department of Materials Science and Engineering, Clemson University, Clemson, SC 29634. Contact e-mail: [email protected]. edu N.A. MARA, Staff Scientist, is with the Center for Integrated Nanotechnologies and the Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, NM 87545. R.L. SCHOEPPNER, Research Student, is with the School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164. R.R. UNOCIC, Research Staff Scientist, is with the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831. M.S. KENNEDY, Associate Professor, is with the Department of Materials Science and Engineering, Clemson University, and also with the Center for Optical Materials Science and Engineering Technologies at Clemson University, Clemson, SC 29634. Contact e-mail: [email protected] Manuscript submitted June 1, 2015. Article published online January 13, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
could be seen for a system’s real-world application.[9] In order to enhance wear resistance of a tribosystem, coatings can be applied.[11] Monolithic coatings have been used,[11] but recently multicomponent layered systems have been explored for their desirable wear characteristics.[10,12] Nanoscale metallic multilayers (NMMs) are one specific layered system that has shown promise for use in applications that require wear-resistance. NMM systems are composed of bonded stacks of alternating metallic layers with sub-100 nm individual layer thicknesses. This small layer thickness leads to a very high density of layer interfaces,[13] which in turn imparts high hardness while retaining appreciable ductility.[14] These properties make them particularly useful as freestanding high-strength foils,[15] wear-resistant coatings,[16] and potentially microelectromechanical systems (MEMS) electrical contacts.[17] However, for such systems to become practical, particularly in terms of long-term durability, wear response and its underlying mechanisms must first be determined. Studies have previously examined initial wear properties of NMM systems, and have highlighted their potential as deformation-resistant systems.[3,16] When coherent and semi-coherent NMM systems have been studied under scratch[3] and wear[16] conditions, it
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