Deformation energies and mechanism during Vickers nanoindentation in lanthanum ultra- and metaphosphate glasses

Abstract

Elastic and plastic deformation energies during Vickers nanoindentation (penetration depth h t =0.3–1.0 μm) at room temperature (humidity 48%) of lanthanum phosphate glasses with different network structures (ultraphosphate 10La 2O 3·90P 2O 5 and metaphosphate 25La 2O 3·75P 2O 5 glasses (mol%)) were estimated. 10La 2O 3·90P 2O 5 glass has values of the Martens (universal) hardness MH=3.31±0.05 GPa, elastic recovery E R=0.60, elastic deformation energy U e=130±5 kJ/mol and plastic deformation energy U p=88±5 kJ/mol at h t=1.0 μm. 25La 2O 3·75P 2O 5 glass shows MH=2.78±0.05 GPa, E R=0.56, U e=102±5 kJ/mol and U p=79±5 kJ/mol. It is suggested that the metaphosphate glass with a two-dimensional network structure is more readily deformed during indenter loading compared with the ultraphosphate glass with a three-dimensional network structure. The main origin of plastic deformation at h t<1.0 μm is considered to be densification. It is proposed that the deformation energy at the nanoindentation level in the glass is closely related to the mean atomic volume of the glass.