1 INDENTATION TOPOMETRY IN GLASSES BY ATOMIC FORCE MICROSCOPY Tanguy ROUXEL (*) , Claude MOYSAN, Vincent KERYVIN and Jean-Christophe SANGLEBŒUF, LARMAUR, FRE-CNRS 2717, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex, France tanguy.rouxel@univ-rennes.fr Abstract - Information regarding the mechanical behavior of a material can be obtained by means of indentation experiments either from the load-displacement curve or from the analysis of the geometrical characteristics of the indentation. Although the first method has motivated numerous studies in the past 15 years, the latter one (indentation topometry) gives a different and complementary view of the indentation behavior. In all cases, the ratio (γ) between the total penetration displacement and the contact depth is a key parameter for the determination of Young's modulus by means of indentation methods. Although γ is usually taken as a constant, it was found to range between 0.8 and 1.3, depending both on the indentation load and on the glass composition. A good correlation was found between γ and Poisson’s ratio. For silica- rich silicate glasses, which show a limited elastic recovery and exhibit a large contact surface area with the indenter, γ is close to 0.9. On the contrary, γ approaches π/2, the theoretical value in the case of pure elasticity, for a ZrCuAlNi bulk metallic glass and for covalent glasses from the Ge-Se system, which show a remarkable elastic recovery and a small contact area. In addition, in this latter glass forming system, the indentation size was found time-dependent. (Key-words: indentation, contact mechanics, elastic recovery, deformation mechanism) 1. Introduction The study of glasses with different mechanical properties allows for an interesting comparison between theoretical and experimental evaluations of the elastic recovery. Among the important phenomena which were observed and are discussed in this paper, piling-up versus sinking-in of matter around the indentation edges and volume conservative shear flow versus flow-densification process are of primary interest. The reversible and permanent displacement components along the loading axis were systematically measured by atomic force microscopy (AFM) and further used to get insight into the mechanical behavior. This method provides an interesting alternative to the already widely used indentation load/displacement methods (nanoindentation equipments). In these indentation-depth-sensing methods, material properties cannot be precisely estimated in a self-consistent manner due to the lack of accurate information regarding the indentation morphology and for instance the contact area. A method based on an energy principle approach of the depth-sensing hardness measurements was proposed by Sakai [1] to avoid this problem. However, parameters such as the effective contact-surface area and the true indentation volumes, which involves the effective indentation shape, still come into play and greatly affect the results. It seems therefore that a systematic study allowing to get more insight into the indentation morphology is required to go further towards the understanding and the analysis of indentation. 2. Materials and experimental methods SiO 2 , standard soda-lime-silica float, GeSe 4 and Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glasses were studied (see ref. [2,3] for details regarding the synthesis method, composition and properties of the different glasses). All glasses were carefully annealed for 30 min at Tg prior to testing. The elastic moduli were first calculated from the measurements of the longitudinal, V l , and transverse, V t , ultrasonic wave velocities with a better than ± 2 % relative error by means of 10 MHz piezoelectric transducers. Young's modulus, E, and Poisson's ratio, ν, derive from the classical elasticity relationships [4]. The density was measured at 20°C by the Archimedean displacement technique using CCl 4 . The relative error on the density is ± 0.5 %. The indentation behaviour was investigated using a Vickers