Scratch resistance of Al/SiC metal/ceramic nanolaminates
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Al/SiC nanolaminates have been shown to possess excellent combination of mechanical strength and flexibility. While metal–ceramic multilayers present a tremendous opportunity for hard coatings, the strength evaluation is usually carried out under static loading conditions such as nanoindentation and microcompression testing. In this study, we have studied the scratch resistance behavior of Al/SiC nanolaminates. These properties are then compared to monolithic films of Al and SiC. Finally, the deformation behavior under such loading was quantified by critical load, work of deformation, and postexperimental microstructural analysis by scanning electron microscopy and focused ion beam cross sections. It is shown that the combination of hard SiC and plastic Al layers provides enhanced resistance to scratch loading and makes these materials as very good candidates for wear-resistant coatings.
I. INTRODUCTION
Multilayered nanoscale materials have been shown to exhibit unique electrical,1–3 magnetic,4 optical,5,6 and mechanical properties.7–9 In many of these applications, these materials are subjected to a variety of dynamic loading situations10 such as wear and abrasion that lead to degradation and failure.11 Metal–ceramic nanolaminates have emerged as promising candidates as hard and tough coatings.12–17 These materials exhibit a good combination of strength, hardness, and toughness.8,9,18–22 To date, an understanding of deformation in these materials has been limited to static loading such as nanoindentation23,24 and micropillar compression.25,26 Although such methods provide a good fundamental understanding of the mechanical response and deformation mechanisms in these materials, a direct understanding of their deformation under wear and sliding conditions has not really been examined. Scratch testing has been used recently to probe the tribological properties of multilayered materials.14–17 Tribological behavior on the small scale has become increasingly important with the advent of micro- and nanomechanical devices. During scratch testing, both normal and tangential forces are applied during dynamic loading. Usually, an indenter tip is moved across the sample surface with increasing normal load. As the load increases, various fracture processes can occur such as cracking, delamination, coating spalling, and buckling.27,28 The load at the onset of the fracture process is defined as the critical load.27,29 Although the critical load a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.274 278
J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
is dependent on test conditions such as indenter geometry and loading rate,27 it can be used as a good comparative tool for the evaluation of different materials tested under similar conditions.30 In addition, scratch deformation can be quantified by of postscratch microstructural characterization.10,14,30–32 In this study, we have studied the scratch resistance of Al/SiC metal–ceramic nanolaminates and compared their behavior to that of monolith
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