Indentation topometry in glasses by atomic force microscopy

Young’s moduli of glasses belonging to different compositional systems were estimated from Vickers micro-indentations by means of a atomic force microscopy analysis combined with confocal microscopy observations of the indentation morphology. The way matter flows beneath the indenter (densification or volume conservative shear flow) plays a major role on the estimation method. The ratio (γ) between the total penetration displacement and the contact depth is a key parameter and 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. An expression was proposed to calculate Young’s modulus from the geometrical characteristics of the indentation, accounting for the actual value of γ.