Mechanical characterization for β-Sn single crystals using nanoindentation tests O. Şahin a, ⁎ , O. Uzun b , U. Kölemen b , N. Uçar a a Department of Physics, Art and Science Faculty, Süleyman Demirel University, Isparta, Turkey b Department of Physics, Art and Science Faculty, Gaziosmanpaşa University, Tokat, Turkey ARTICLE DATA ABSTRACT Article history: Received 12 June 2006 Received in revised form 23 February 2007 Accepted 28 February 2007 Depth-sensing nanoindentation tests were made on β-Sn single crystals having different growth directions. The indentation load-displacement curves of the samples were obtained under different peak loads ranging from 10 to 50 mN. The most commonly used Oliver–Pharr method was used to analyze the unloading segments of these curves. It was found that the dynamic nanohardness (H d ) and reduced elastic modulus (E r ) exhibited significant peak load dependence. The observed size dependence of the H d was rationalized using classical Meyer's law, Proportional Specimen Resistance (PSR) and the Modified Proportional Specimen Resistance (MPSR) model. Reduced elastic modulus-indentation test load curves exhibited distinct transition to a plateau of constant E r . It can be concluded that the transition in such curves correspond to the intrinsic E r value of the examined materials. The examined single crystals also exhibit pop-in phenomenon attributed to the onset of dislocation nucleation activity underneath the indenter. © 2007 Elsevier Inc. All rights reserved. PACS: 62.20. Qp.20.-x 62.20. Fe 62.20. Dc Keywords: Nanoindentation test Nanohardness β-Sn single crystal Indentation size effect Pop-in effect 1. Introduction Indentation hardness has been the most commonly used technique to measure the mechanical properties of materials. It has been considered as a principal parameter for mechan- ical characterization of materials. One reason for the current focus on investigating the earliest stages of deformation in an indentation hardness test stems from interest in under- standing the role of plastic deformation. Another reason is to investigate the cause(s) of a greater hardness often being measured either for smaller applied test loads or at smaller indentation sizes, frequently specified as an indentation size effect (ISE) that produces a greater hardness at a smaller applied load. Lastly, there is the notion that careful monitoring of the earliest stages of plastic deformation at smaller indentations will help to better understand the fundamental nature of the indentation hardness test itself. Of course, all of these interests are promoted by the advanced capabilities that are now available to very sensitively monitor both the indenting load/deformation behaviors and to make observa- tions of the nature of the indented material structure [1]. Two methods of Vickers microindentation hardness mea- surement are in use. In one method, a hard indenter (i.e., a Vickers diamond pyramid) penetrates into the solid with a constant load. After unloading, the dimensions of the indentation in the solid are measured and the hardness, defined as the ratio of the load to the facet contact area of the indentation determined. The method is known as conven- MATERIALS CHARACTERIZATION 59 (2008) 427 – 434 ⁎ Corresponding author. Tel.: +90 246 211 40 48; fax: +90 246 237 11 06. E-mail address: sahin@fef.sdu.edu.tr (O. Şahin). 1044-5803/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.matchar.2007.02.016