Indentation topometry in glasses by atomic force microscopy
Résumé
The ratio (gamma) 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 gamma 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 gamma 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, gamma is close to 0.9. On the contrary, gamma approaches pi/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.