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NANOINDENTATION is a technique which has been used recently to determine the mechanical properties and characterizes the mechanical behavior of materials and thin films at nano- and micro-scales. An important feature of these experiments is the deformation of the material around the contact area: sinking-in (deformation downward with respect to the indented surface plane) and piling-up (deformation upward). For isotropic materials, the generation of pile-ups and sinkins in indentation tests is correlated with material properties.[1] Maximum pile-up is observed in the case of elastic-perfectly plastic materials, where strain hardening does not occur. The maximum sink-in appears when the indented material exhibits a strong strain hardening. For a specific material, with moderate strain hardening there is neither pile-up nor sink-in, and then the boundary of contact can be determined as a crosssection of the tip under loading and a surface of the sample prior to the deformation. The symmetry of pileup corresponds to the symmetry of the applied indenter tip; an axis-symmetric tip generates axis-symmetrical pile-up, and three and four pile-ups occur as a result of Berkovich and Vickers indentation, respectively. The mode of material deformation in the vicinity of a contact boundary, that is, formation of a pile-up or a sink-in, depends uniquely on the material properties and not on the applied load. Therefore, pile-up and sink-in patterns can provide useful information about the mechanical behavior of the investigated material. STANISŁAW KUCHARSKI, Head, and DARIUSZ JARZA ˛ BEK, Assistant, are with the Surface Layer Laboratory, Institute of Fundamental Technological Research, Pawin´skiego 5b, 02-106 Warsaw, Poland. Contact e-mail: [email protected] Manuscript submitted April 3, 2014. Article published online July 10, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A

Nevertheless, in the case of anisotropic material, the response around the impression is more complex. Hence, much research in recent years has focused on the anisotropy associated with nanoindentation tests of a single crystal in different crystallographic orientations. Some initial attempts focusing on this topic can be found in the work of Vangroenou and Kadijk.[2] More recently, Wang et al.[3] presented a study of the dependence of nanoindentation pile-up patterns and microtextures on the crystallographic orientation using high purity copper single crystals. Their results showed that the pile-up patterns on the surfaces of (001)-, (011)-, and (111)-oriented single crystals have four-, two-, and six-fold symmetry, respectively. They evaluated the crystallographic directions in which the pile-ups should appear for specific oriented surfaces and they observed that at ambient temperature the active glide systems of copper consist of (111) glide planes and h110i slip directions. A similar effect was also observed by Liu et al.[4] and was compared with finite element simulations. However, in this work, threefold instead of sixfold symmetry was observed in the