Ceramics-Silikáty 54 (3) 225-234 (2010)

GLASS HARDNESS AND ELASTIC MODULUS DETERMINATION BY NANOINDENTATION USING DISPLACEMENT AND ENERGY METHODS

A. Chorfa , M. A. Madjoubi , M. Hamidouche , N. Bouras , J. Rubio , F. Rubio

A comparative experimental study on the determination of hardness and elastic modulus of two glasses (soda lime glass and borosilicate glass) by nanoindentation was made using Oliver and Pharr displacement analysis (O&P method) and two methods based on the energy of deformation developed by Cheng and Cheng (C&C) and Chen and Bull (C&B). Multiloading indentations with peak loads varying between 5 mN and 500 mN were performed on a Micro Materials Ltd Nano Test static equipment system using a Berkovich indenter. The implemented calibrations in O&P analysis taking into account of thermal drift, initial depth, instrument compliance and indenter geometry sources of error, revealed their relative importance on the measured properties H_IT and E_r. The errors induced by the estimated initial depths and the thermal drift on these properties remain limited in comparison to those caused by the instrument compliance and the indenter geometry. The implementation of the instrument compliance Cf was verified by linear regression of the measured compliance variation and also by examining the constancy of the parameter F_max/S² (ratio of the peak load over the contact stiffness squared) at large depths. The calibrated surface area has an important influence on H_IT at small depths. The use of C&C linear energy method showed that there is no unique value for the indenter constant λ that is appropriate for both glasses. The comparison between the two energy methods showed that the results obtained by the linear C&C method with a constant λ =5.3 are closer to those obtained by the non linear energy C&B method. The soda lime glass hardness and elastic modulus obtained by these two methods are closer to the values obtained by conventional means. The borosilicate glass conventional values are rather closer to those obtained by O&P method.

Keywords: Nano indentation, Glasses, Hardness, Elastic modulus