Micropillar compression of Al/SiC nanolaminates D.R.P. Singh a , N. Chawla a,⇑ , G. Tang b , Y.-L. Shen b a Materials Science and Engineering, Arizona State University, Tempe, AZ 85287-6106, USA b Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM, USA Received 1 April 2010; received in revised form 12 August 2010; accepted 14 August 2010 Available online 9 September 2010 Abstract Al/SiC nanolaminates possess an excellent combination of mechanical strength and flexibility. While nanoindentation provides a rea- sonable estimate of the mechanical properties such as Young’s modulus and hardness of these materials, the stress state under nanoin- dentation is extremely complex. Micropillar compression has become an attractive method of studying the mechanical properties of materials at small length scales in a nominally homogeneous stress state. In this work, micropillars of Al/SiC nanolaminate were fabri- cated using focused ion beam milling. Compression testing was carried out using a flat-end nanoindenter head. The actual displacement of the pillar during micropillar compression was deconvoluted by subtracting the “extraneous” displacements of the system. Fracto- graphic analysis showed that Al squeezes out between the SiC layers and that a mutual constraint is observed between the hard and soft layers. Numerical finite element modeling was also employed to provide physical insight into the deformation features of the multilayered pillar structure and agreed well with the experimental observations. Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Nanoindentation; Micropillar compression; Nanolaminate; Focused ion beam 1. Introduction Multilayered materials at the nanoscale exhibit unique electrical [1–3], magnetic [4], optical [5,6] and mechanical properties [7–9]. Metal–ceramic systems, in particular, can be tailored to obtain a combination of high strength, hardness and toughness [8–14]. Nanoindentation has been used extensively to probe the modulus and hardness of homogeneous bulk materials and thin films. In multilay- ered materials, however, it has been shown that a highly complex and inhomogeneous stress state is developed under the indenter [11,15]. Furthermore, the multilayered structure results in complex plasticity, which can take place even during unloading [15,16]. A more straightforward way of obtaining nominally uniaxial stress–strain response at small volumes is by microcompression of pillars [17]. Pillars in the micrometer range, or smaller, can be fabricated by the focused ion beam (FIB) technique [17–21]. These pillars are then com- pressed using a flat punch in a nanoindenter, or by scan- ning electron microscopy (SEM). This method has recently been used to study the mechanical response of metallic single crystals [22,23], metallic alloys [24] and metallic nanolaminates [25]. This paper reports on the microcompression behavior of model Al/SiC nanolaminates. The pillars were fabricated by FIB and tested in compression using a nanoindenter. The effect of pillar taper was studied. The evolution of damage was quantified by interrupted experiments and cross-sectioning of deformed pillars, also with the FIB. The finite element method (FEM) was used to model the deformation behavior of the pillars numerically and to pro- vide a mechanistic understanding of deformation. 2. Materials and experimental procedure Al/SiC multilayer samples were synthesized by physical vapor deposition, using magnetron sputtering. Details of the sputtering method are discussed elsewhere [11–13]. 1359-6454/$36.00 Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2010.08.025 ⇑ Corresponding author. E-mail address: nchawla@asu.edu (N. Chawla). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 58 (2010) 6628–6636