Universal hardness and elastic recovery in Vickers nanoindentation of copper phosphate and silicate glasses

Abstract

Load/unload displacement (penetration) curves for yCuOx·(100−y)P2O5 glasses (y=45, 50) with different copper valence states, silica and soda-lime silicate glasses at room temperature (humidity ∼64%) have been measured using a Vickers nanoindentation technique, and universal hardness Hu and elastic recovery ER have been estimated in the load range of 0.1–1 N. Copper phosphate glasses have the values of Hu=1.7–2.5 GPa and ER=0.55–0.65, depending on the Cu+/Cu2+ ratio. The glasses with high Cu+ contents show large densifications (plastic deformation) during loading and small elastic recoveries during unloading compared with the glasses with no Cu+ ions. These deformation behaviors are well explained qualitatively by considering lower coordination number and more covalent bonding of Cu+ compared with Cu2+, which have been confirmed from X-ray photoelecton spectra. Silica glass has ER≒0.77, which is large compared with ER≒0.63 in a soda-lime silicate glass. This large difference leads to the smaller value in Hu of silica glass than that of a soda-lime silica glass. It is confirmed that load displacement curves in nanoindentation tests are well fitted with quadratic equations.